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Notes: The kinetics of the thermal reaction between CF3OF and C3F6 have been investigated between 20 and 75°C. It is a homogeneous chain reaction of moderate length where the main product is a mixture of the two isomers 1-C3F7OCF3 (68%) and 2-C3F7OCF3 (32%). Equimolecular amounts of CF3OOF3 and C6F14 are formed in much smaller quantities. Inert gases and the reaction products have no influence on the reaction, whereas only small amounts of oxygen change the course of reaction and larger amounts produce explosions.The rate of reaction can be represented by eq. (I): The following mechanism explains the experimental results: Reaction (5) can be replaced by reactions (5a) and (5b), without changing the result: Reaction (4) is possibly a two-step reaction: \documentclass{article}\pagestyle{empty}\begin{document}$$ E_1 = 15.90 \pm 0.45{\rm kcal}\,{\rm mol}^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = \left( {7.60 \pm 0.68} \right)10^8 {\rm exp}\left( { - 15,900\,\, \pm \,\,450\,\,{{{\rm cal}} \mathord{\left/ {\vphantom {{{\rm cal}} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right)M^{ - 1} \cdot s^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ E^ * \, = \,12.30\, \pm \,0.25\,{\rm kcal}\,{\rm mol}^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k^ * \, = \,\left( {6.11\, \pm \,0342} \right)10^7 \,{\rm exp}\left( { - 12,300\, \pm \,250\,{{{\rm cal}} \mathord{\left/ {\vphantom {{{\rm cal}} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} \right)M^{ - 1} \, \cdot \,{\rm s}^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {E^ * \, - \frac{1}{2}E_1 \, = \,4.35\,{\rm kcal}\, = \,E_3 \, - \,\frac{1}{2}E_4 ;} & {E_3 \,} \\ \end{array} 〉 \,4.35\,{\rm kcal} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \nu \,\left( {{\rm chain}\,{\rm length}} \right)\, = \,1 + \,\frac{{k_3 }}{{k_1 ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} \left( {2k_4 } \right)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} }}\left( {\frac{{\left| {{\rm CR}_{\rm 3} {\rm OF}} \right|}}{{\left| {{\rm C}_{\rm 3} {\rm F}_{\rm 6} } \right|}}} \right)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $$\end{document} For ∣CF3 = ∣C3F6∣, ν20°C = 36.8, ν50°C = 24.0, and ν70°C = 14.2.

Notes: The rate of the perchloric acid hydrolysis of aqueous ethyl and butyl vinyl ethers at 25.0°C, in the presence of micellar aggregates [anionic, sodium dodecyl sulfate (SDS); cationic, cetyl trymethyl ammonium bromide (CTAB); and nonionic, polyoxyethylen—23—dodecanol, (Brij 35)], has been studied. Negligible effects were observed in the cases of cationic and nonionic micelles. Anionic micelles produce an enhancement in the reaction velocity, and the rate constants go through maxima with increasing SDS concentration. These maxima disappear in the presence of excess sodium perchlorate. All these facts are interpreted quantitatively by means of the pseudo-phase ion-exchange model.

Notes: The recent experiments on the chloride-assisted dealkylation of alkylcobalamins by a variety of oxidants (IrCl62-, AuCl4-, Fe(H2O)5Cl2+, and PtCl62-), which are scattered in several previous publications, and their general kinetic characteristics are summarized. The kinetic studies are also extended to include the dealkylations of (methylaquo)-3,5,6-trimethylbenzimidazolylcobamide and protonated base-off ethylcobalamin by IrCl62- (1.0M Cl-) and by Fe(III) ions at 0.1M Cl-, and the demethylation of (methylaquo)-3,5,6-trimethylbenzimidazolylcobamide by AuCl4- (1.0M Cl-). This extension is in an effort to substantiate the general mechanism which has been previously proposed for these oxidative dealkylations. The general kinetic characteristics are described in terms of a preassociation of the reactants, followed by a rate-determining electron-transfer process to yield the R-B12+ radical, which then undergoes further reactions to produce the products observed. The overall reactions are discussed within the framework of chlorine-bridging inner sphere electron-transfer reactions.

Notes: Hydrogen abstration from H2S by CF3 radicals, generated by the photolysis of both CF3COCF3 and CF3I, has been studied in the temperature range 314-434 K. The rate constant, based on the value of 1013.36 cm3/mol · s for the recombination of CF3 radicals, is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log }\,k_2 \, = \,\left( {12.20\, \pm \,0.05} \right)\, - \,{{\left( {19,220\, \pm \,360} \right)} \mathord{\left/ {\vphantom {{\left( {19,220\, \pm \,360} \right)} {19.145T}}} \right. \kern-\nulldelimiterspace} {19.145T}} $$\end{document} with CF3COCF3 as the radical source, and \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log }\,k_2 \, = \,\left( {12.00\, \pm \,0.07} \right)\, - \,{{\left( {18,270\, \pm \,470} \right)} \mathord{\left/ {\vphantom {{\left( {18,270\, \pm \,470} \right)} {19.145T}}} \right. \kern-\nulldelimiterspace} {19.145T}} $$\end{document} with CF3I as the radical source, where k2 is in cm3/mol · s and E is in J/mol. These results resolve a previously existing controversy concerning the values of the rate constants for this reaction. They show that CF3 radicals are less reactive than CH3 radicals in attacking H2S, and this behavior indicates that polar effects play a significant role in the hydrogen transfer reactions of CF3 radicals.

Notes: A vacuum ultraviolet photolysis of C2H5Br at 147 nm was studied over a pressure range of 0.5-50 torr at 298 K. The effects of additives He and NO were also investigated.The principal reaction products were found to be C2H4 and C2H6, with lesser yields of CH4 and C2H2. With increasing pressure the product quantum yields Φi of C2H4, CH4, and CH2H6 remained constant, while that of C2H2 decreased from 0.03 to almost 0. The effect of He as an additive was found to be extremely small on the quantum yields of the major products. Addition of NO completely suppresses the formation of CH4, C2H2, and C2H6, and reduces partially the production of C2H4. The primary processes appear to involve two electronically excited states. One state mainly yields C2H4 by molecular elimination of HBr and is thought to be due to a Rydberg transition. The other state decomposes to C2H5 and Br radicals by C—Br bond fission. These two competitive reaction modes contribute to the photodecomposition in proportions of 50% and 50%. The extinction coefficient for C2H5Br at 147 nm and at 298 K has been determined as ∊ = (1/PL) In(Io/It) = 712 ± 7 atm-1 · cm-1.

Notes: The product quantum yields in the photolysis of 2,2,4,4-tetramethyl-3-pentanone have been measured in homogeneous solvents of different viscosities, in micellar solutions of cetyltrimethylammonium chloride and sodium dodecyl sulfate, and in dioctadecyl ammonium chloride vesicles.The product quantum yield in n-heptane was found to be 1. This value decreases to 0.5 in paraffin oil as a consequence of geminate recombination. In the presence of free radical scavengers, the extent of geminate disproportionation can be evaluated from the yields of isobutene and 2,2-dimethyl propionaldehyde. From these yields and the geminate recombination yields the total amount of geminate processes and the disproportionation-to-combination ratio for caged radicals are estimated. It is found that micelles provide the most efficient cages. In these media only about 10% of the radicals avoid cage processes. The disproportionation-to-combination ratio of tert-butyl and pivaloyl radicals was found to be extremely media dependent. The measured values ranged from about 0.2 in paraffin oil to 0.8 in cetyltrimethylammonium chloride micelles.

Notes: Kinetics of the thermal decomposition of acetic acid vapor dilute in argon have been studied over the temperature range of 1300-1950 K in a single-pulse shock tube. The acid was found to decompose homogeneously and molecularly via two competing firstorder reaction channels at nearly equal rates, to form methane and carbon dioxide on the one hand, and ketene and water on the other. Fall-off behavior has been taken into account and limiting high-pressure rate constants for both channels have been derived. Ketene was found to decompose both unimolecularly to methylene radicals and carbon monoxide and also by a radical reaction with CH2 to form ethylene and carbon monoxide. The rate constant derived for the unimolecular reaction was found to be in good agreement with an earlier shock tube measurement by H. G. Wagner and F. Zabel [Ber. Bunsenges Phys. Chem., 75, 114 (1971)]. The bimolecular reaction of ketene to produce allene and carbon dioxide, important in lower temperature reaction systems, has been found to be unimportant under the present conditions. A computer model for the decomposition kinetics involving 46 reactions of 21 species has been found to simulate the experimental yield data substantially. Sensitivity analyses have been used to identify reactions which make important contributions to the overall mechanism and yields of major products. Methylene radicals play important roles in determining yields of major species.

Notes: The abstraction of hydrogen/deuterium from CH3CH2Cl, CH3CHDCl, and CH3CD2Cl by photochemically generated ground-state chlorine atoms has been investigated over the temperature range of 8-94°C using methane as a competitor. Rate constant data for the following reactions have been obtained:The temperature dependence of the relative rate constants ki/kj was found to conform to the Arrhenius rate law, where the stated error limits are one standard deviation:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 /k_2 = (1.099 \pm 0.015)\exp [(429 \pm 2)/T] $$ $$ k_1 /k_r = (1.422 \pm 0.026)\exp [(1113 \pm 3)/T] $$ $$ k_2 /k_r = (1.295 \pm 0.029)\exp [(684 \pm 3)/T] $$ $$ k_3 /k_r = (1.177 \pm 0.025)\exp [(717 \pm 4)/T] $$ $$ k_4 /k_r = (1.115 \pm 0.023)\exp [(732 \pm 2)/T] $$ $$ k_5 /k_r = (0.978 \pm 0.020)\exp [(985 \pm 2)/T] $$\end{document} and kr is the rate constant for the reference reaction (CH4 + Cl → CH3 + HCl). The β secondary kinetic isotope effects (k2/k3/k4) are close to unity and show a slight inverse temperature dependence. Both preexponential factors and activation energies decrease as a result of deuterium substitution in the adjacent chloromethyl group. The trends are well outside the limits of experimental error.

Notes: The technique of laser photolysis of alkyl and perfluoroalkyl iodides at 266 nm followed by time-resolved detection of the 1.3-μm emission from I*(2P1/2) has been used to measure the rate constants for deactivation of I* by CH3I, C2H5I, CF3I, and CH4. The recommended values are (2.76± 0.22) × 10-13, (2.85 ± 0.40) × 10-13, (3.5 ± 0.5) × 10-17, and (7.52 ± 0.12) × 10-14, respectively, in units of cm3 molecule-1 S-1.

Notes: The reactions of labeled N15NO+ with CO, NO, O2, 18O2, N2, NO2, and N2O have been investigated using a tandem ICR instrument. In each case the total rate coefficient, product distribution, and kinetic energy dependence were measured. The results indicate that very specific reaction mechanisms govern these reactions. This conclusion is suggested by the lack of isotopic scrambling in many cases and by the complete absence of energetically allowed products in almost all of the systems. The kinetic energy studies indicate that most of the reaction channels proceed through an intermediate complex at low energies and via a direct mechanism at higher kinetic energies. Such direct mechanisms include long range charge transfer and atom or ion transfer.

Notes: The reaction of CH4 + Cl2 produces predominantly CH3Cl + HCl, which above 1200 K goes to olefins, aromatics, and HCl. Results obtained in laboratory experiments and detailed modeling of the chlorine-catalyzed polymerization of methane at 1260 and 1310 K are presented. The reaction can be separated into two stages, the chlorination of methane and pyrolysis of methylchloride. The pyrolysis of CH3Cl formed C2H4 and C2H2 in increasing yields as the degree of conversion decreased and the excess of methane increased. Changes of temperature, pressure, or additions of HCl had little effect. In the absence of CH4 C2H4 and C2H2 are formed by the recombination of ĊH3 and ĊH2Cl radicals. With added CH4 recombination of ĊH3 forms C2H6, which dehydrogenates to C2H4 + H2. C2H4 in turn dehydrogenates to C2H2 + H2. While HCl, C, CH4, and H2 are the ultimate stable products, C2H4, C2H2, and C6H6 are produced as intermediates and appear to approach stationary concentrations in the system. Their secondary reactions can be described by radical reactions, which can lead to soot formation. ĊH3 - initiated polymerization of ethylene is negligible relative to the Ċ2H3 formation through H abstraction by Cl. The fastest reaction of Ċ2H3 is its decomposition to C2H2. About 20% of the consumption of C2H2 can be accounted for by the addition of Ċ2H3 to it with formation of the butadienyl radical. The addition of the latter to C2H2 is slow relative to its decomposition to vinylacetylene. Successive H abstraction by Cl from C4H4 leading to diacetylene has rates compatible with the experimental values. About 10% of Ċ4H5 abstracts H from HCl and forms butadiene. Successive additions of Ċ2H3 to butadiene and the products of addition can account for the formation of benzene, styrene, naphthalene, and higher polyaromatics. The following rate parameters have been derived on the basis of the experimentally measured reaction rates, the estimated frequency factors, and the currently available heat of formation of the Ċ2H3 radical (69 kcal/mol): \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\mathop {{\rm C}_{\rm 2} }\limits^. {\rm H}_{\rm 3} \mathop {\longrightarrow}\limits_{\left( {\rm M} \right)}^{39} {\rm H}\,\, + \,\,{\rm C}_{\rm 2} {\rm H}_{\rm 2} } & {\log k\left( {1\,{\rm atm,}\,{\rm 1300}\,{\rm K}} \right)\, = \,5.2\, + \,0.3\,s^{ - 1} } \\ \end{array} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm C}_{\rm 2} {\rm H}_{\rm 4} \, + \,\mathop {{\rm C}_{\rm 2} }\limits^. \,\mathop {\longrightarrow}\limits^{17} \,\mathop {{\rm C}_{\rm 4} }\limits^. {\rm H}_{\rm 7} } \hfill & {E\, \ge \,2\, \pm \,2\,{{{\rm kcal}} \mathord{\left/ {\vphantom {{{\rm kcal}} {{\rm mol}}}} \right. \kern-\nulldelimiterspace} {{\rm mol}}}\,} \hfill \\ {\mathop {{\rm C}_{\rm 2} }\limits^. {\rm H}_{\rm 5} \, + \,{\rm C}_{\rm 6} {\rm H}_{\rm 6} \,\mathop {\longrightarrow}\limits^{40} \,\mathop {{\rm C}_{{\rm 12}} }\limits^. {\rm H}_{{\rm 11}} } \hfill & {E\, = \,11\, \pm \,2\,{{{\rm kcal}} \mathord{\left/ {\vphantom {{{\rm kcal}} {{\rm mol}}}} \right. \kern-\nulldelimiterspace} {{\rm mol}}}} \hfill \\ \end{array} $$\end{document}

Notes: The kinetics of fast elementary recombination of neutral ketyl radicals of benzophenone and its four derivatives (BPH⋅), the dismutation of benzophenone radical anions, the disproportionation between BPH⋅ and stable nitroxyl radicals, (), and the electron transfer have been investigated in both individual solvents and binary mixtures of different viscosities. Reaction (1) for unsubstituted BPH in water, water glycerol, and n-hexane is controlled by diffusion with 2k1 ≃ kdiff. In aliphatic alcohols and toluene, which form solvation complexes with BPH⋅, reaction (1) is diffusion-enhanced and activation-controlled, respectively, with 2k1 〈 kdiff. In a viscous solvent such as 1-propanol-glycerol mixture (100 ≲ η ≲ 450 cP) reaction (1) is diffusion-controlled. Reaction (2) in alkaline 1-propanol and alkaline 1-propanol-glycerol mixture is activation controlled. The rates of reactions (3) and (4) for benzophenone radicals and nitroxyl radicals of the imidazoline series decrease as the viscosity of the water-glycerol and 1-propanol-glycerol mixtures is increased. The reactions are molecular mobility limited; nevertheless, the numerical values of k3 (k4) are 2-6 times as small as the corresponding kdiff values due to the low steric factor of the reactions (therefore called pseudodiffusion-controlled reactions). The theoretical estimates of k3 (k4) are in good agreement with the experimental results. The elimination of spin forbiddance in the process of radical recombination in viscous solvents is discussed.

Notes: Methods are described for including the participation of bound electronically excited states in calculations on radical recombination reactions. These methods are illustrated by applying them to the reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm O}\left( {^{\rm 3} P} \right)\,\, + \,{\rm O}\left( {^{\rm 3} P} \right)\,\, + \,\,{\rm M} \to {\rm O}_{{\rm 2}\,} \,\, + \,\,{\rm M}\,} \\ {{\rm O}\left( {^{\rm 3} P} \right)\,\,\, + \,\,{\rm NO}\left( {{\rm X}^{\rm 2} {\rm II}} \right)\, + \,\,{\rm M} \to {\rm NO}_{{\rm 2}\,} \,\, + \,\,{\rm M}} \\ {{\rm OH}\left( {{\rm X}^{\rm 2} {\rm II}} \right)\,\, + \,\,{\rm NO}_{\rm 2} \left( {\tilde X^2 A_1 } \right)\, + \,\,{\rm M} \to {\rm HNO}_{3\,} \,\, + \,\,{\rm M}\,\,\,} \\ \end{array} $$\end{document} For O2, accurate ab initio potentials are used in calculations which show that the electronic degeneracy and long-range part of the potential are likely to be crucial in determining the contribution of a given electronic state to the overall reaction, as long as the state is not so weakly bound that it dissociates thermally before being electronically quenched. Weak collision effects are allowed for using a Monte Carlo technique and an assumed exponential form for the distribution of energies transferred in collisions with a third body. For larger systems it is evident that the role of bound excited states in the low-pressure regime falls rapidly as the size of the system increases. As the high-pressure limit is approached, however, the contribution of excited states is likely to come close to that expected simply on the basis of electronic degeneracy.

Notes: The approximations developed to determine the energy distribution function of molecules activated above energy decomposition threshold, from experimental data, have been tested. The approach involved the theoretical (RRKM) calculations of “pseudoexperimental” data for a variety of activated energy distributions. (Single or double Gaussian representations were used in all cases.) Subsequently the algorithms mentioned were applied in order to recuperate the original (i.e., input) energy distributions from these pseudoexperimental data. The results obtained provide strong evidence in favor of the validity of the algorithms and illustrate the necessary requirements for their applications. A trend toward lower accuracy as the energy distributions move to higher energies has been observed. Evidence of the influence of the distribution width is also reported. The origins of the approximation errors have been studied, and ways for further improvement are suggested.

Notes: Relative rate constants for the reaction of OH radicals with a series of branched alkanes have been determined at 297 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10-12 cm3/molecule · s, the rate constants obtained are (× 1012 cm3/molecule · s): isobutane, 2.29 ± 0.06; 2-methylbutane, 3.97 ± 0.11; 2,2-dimethylbutane, 2.66 ± 0.08; 2-methylpentane, 5.68 ± 0.24; 3-methylpentane, 5.78 ± 0.11; 2,2,3-trimethylbutane, 4.21 ± 0.08; 2,4-dimethylpentane, 5.26 ± 0.11; methylcyclohexane, 10.6 ± 0.3; 2,2,3,3-tetramethylbutane, 1.06 ± 0.08; and 2,2,4-trimethylpentane, 3.66 ± 0.16. Rate constants for 2,2-dimethylbutane, 2,4-dimethylpentane, and methylclohexane have been determined for the first time, while those for the other branched alkanes are in generally good agreement with the literature data. Primary, secondary, and tertiary group rate constants at room temperature have been derived from these and previous data for alkanes and unstrained cycloalkanes, with the secondary and tertiary group rate constants depending in a systematic manner on the identity of the neighboring groups. The use of these group rate constants, together with a previous determination of the effect of ring strain energy on the OH radical rate constants for a series of cycloalkanes, allows the a priori estimation of OH radical rate constants for alkanes and cycloalkanes at room temperature.

Notes: The autooxidation of retinyl acetate and methyl retinoate was investigated in chlorobenzene at 45°C. The rates of thermal initiation in the retinyl acetate solutions were measured, and a value was determined of the rate constant for the reaction of oxygen with retinyl acetate (RH + O2 → R· + HO2·): kio = (1.3 ± 0.2) × 10-5 L/mol · s. The number of moles of oxygen absorbed per mole of polyene depends on the substrate concentration. A kinetic scheme for the methyl retinoate autooxidation was proposed which takes into account the isomerization of primary peroxy radicals, and the rate constants for different elementary reactions were estimated. The partial rate constant for “allylic” hydrogen abstraction from retinyl acetate was estimated to be ≥ 1.65 × 103 L/mol · s. A probable propagation sequence was proposed for the autooxidation of retinyl acetate.

Notes: The kinetics of reactions involving halogen atom abstraction from haloalkanes by methyl radicals have been studied in the gas phase. Arrhenius parameters for halogen atom transfer were determined relative to those for methyl radical combination: TextRXlog10A2(L/mol · s)E2(kcal/mol)CFCl38.3 ± 0.210.7 ± 0.4CF3CCl37.9 ± 0.39.7 ± 0.6CF2Cl29.1 ± 0.411.3 ± 0.7CF3Cl8.8 ± 0.511.8 ± 1.0CF3CF2Cl8.3 ± 0.310.9 ± 0.7CF3Br8.6 ± 0.29.3 ± 0.5CF3I8.1 ± 0.14.3 ± 0.2CH3CH2I8.9 ± 0.37.4 ± 0.6The rate data obtained are used to provide information on the importance of polar effects for halogen abstraction processes.

Notes: The advantages and disadvantages of various methods of parametric sensitivity analysis in chemical kinetic modeling are discussed. Particular attention is given to estimates of computational labor for realistic problems, and quantitative comparisons are made utilizing a 52-reaction, 11-species CO oxidation mechanism. The authors′ CHEMSEN/AIM program compares favorably to other techniques in many circumstances, and provides the additional convenience of accepting input information in familiar chemical notation. This paper also reviews recent developments in theory of sensitivity analysis, relevant to chemical kinetic modeling.

Notes: The reactions of CCl3 with O(3P) and O2 and those of CCl3O2 with NO have been studied at 295 K using discharge flow methods with helium as the bath gas. The rate coefficient for the reaction of CCl3 with O was found to be (4.2 ± 0.6) × 10-11 cm3/s and that for CCl3O2 with NO was (18.6 ± 2.8) × 10-12 cm3/s with both coefficients independent of [He]. For reaction between CCl3 and O2 the rate coefficient was found to increase from 1.51 7times; 10-14 cm3/s to 7.88 × 10-14 cm3/s as the [He] increased from 3.5 × 1016 cm-3 to 2.7 × 1017 cm-3. There was no evidence for a direct two-body reaction, and it is concluded that the only product of this reaction is CCl3O2. Examination of these results for CCl3 + O2 in terms of current simplified falloff treatment suggests that the high-pressure limit for this reaction is ∼ 2.5 × 10-12 cm3/s, which may be compared with a direct measurement of the high-pressure limit of 5 × 10-12 cm3/s. A value of (5.8 ± 0.6) × 10-31 cm6/s has been obtained for k0, the coefficient in the low-pressure region. This value is compared with corresponding values found earlier for the (CH3, O2) and (CF3, O2) systems and with estimates based on unimolecular rate theory.

Notes: We report laser absorption measurements of NH3 decay within the flame front region of rich, atmospheric pressure ammonia flames. These data are combined with earlier OH, NH, and NH2 measurements to obtain new estimates for the oscillator strength of NH2. This value, fi = 6.4 × 10-5 for the PQ1,7 line in the (0,9,0) ← (0,0.0) vibrational band of the A2A1 ← X2B1 transition, suggests ΔH°f(NH) ≅ 87 kcal/mol. The ammonia profiles were also combined with previous data on NO, NH, NH2, and OH to provide an extensive database at fuel equivalence ratios (ø) of 1.28, 1.50, and 1.81 for comparison to our kinetic model predictions. This modeling used a one-dimensional flame code which explicitly accounts for the diffusional component in our flame experiments. Modeling results using a conventional mechanism predicted concentration profiles which deviated markedly from our observations. It was possible to obtain much more satisfactory fits by postulating reactions between various NHi (i = 1, 2) species to form N - N bonds. The N2Hj (j = 1-3) species could then lose H atoms via dissociation to ultimately form N2. Inclusion of these reactions in the mechanism allowed us to predict concentration - distance profiles for five different species at three different equivalence ratios that are in good agreement with experiment. The most important component of this mechanism is the recognition that the NHi + NHi reactions dominate the kinetics in rich flames. A most satisfying aspect of these calculations is that the key rate constants in the NHi + NHi sequence were estimated using simple RRK theory.

Notes: The effect of particle size, type of crucible, and heating rate on the thermal curves obtained simultaneously for CuSO4 · 5H2O were discussed. The dissociation steps were confirmed. Thermogravimetric techniques for determining the rate-controlling processes and kinetic parameters were applied for the dehydration steps and the calcination of CuSO4 and CuSO4 · CuO. For the dehydration of the monohydrate one mechanism operates but the activation energy and preexponential factor vary over wide ranges. Differentiating between various mechanisms using the same technique was sometimes difficult giving completely different values for the kinetic parameters. In view of such difficulties the various methods were assessed, the best techniques to treat similar results were recommended and the operating mechanisms and kinetic parameters for the various steps were thus established.

Notes: The kinetics of the gas phase reactions of NO2 with a series of organics have been studied at 295 ± 2 K. It was observed that only 2,3-dimethyl-2-butene and the conjugated dialkenes studied reacted at observable rates, with rate constants which ranged from 1.5 × 10-20 cm3 molecule-1 s-1 for 2,3-dimethyl-2-butene to 1.3 × 10-17 cm3 molecule-1 s-1 for α-phellandrene. These rate constants are compared with the available literature data and the mechanisms of these reactions are discussed.

Notes: Mixtures of NH3 and N2O dilute in Ar were heated behind incident shock waves in the temperature range 1750-2060 K. A cw ring dye laser, tuned to the center of an OH absorption line in the ultraviolet, was used to monitor OH concentration profiles by absorption spectroscopy. Infrared emission was used to follow N2O (at 4.5 μm) and NH3 (at 10.5 μm) concentration - time histories. The early-time NH3 and OH concentration profiles were sensitive to the rate constants of the reactionsleading to the following best-fit expressions for k2 and k3:k2 = 1013.34±0.3 exp(-4470/T) and k3 = 1013.91±0.2 exp(-4230/T) cm3 mol-1 s-1. The results of this study combined with previous low-temperature data suggest a significant non-Arrhenius behavior for both k2 and k3.

Notes: The thermal decomposition of azoisopropane (AIP) was studied in the presence of various quantities of propylene in the temperature and pressure intervals 498-553 K and 3.33-5.33 kPa. The inhibition functions relating to formation of the products were determined; these proved a good basis for interpretation of the formation of the secondary decompositon products of AIP. The experimental data support the conception that the βμ radical - radical reactionoccurs. The product of this is not stable; its decomposition is one of the sources of the secondary products. The ratio of the rate constants was determined for the following reactions:

Notes: The kinetics and mechanism of the thermal decomposition of n-propylsilane have been studied by the single pulse shock tube-comparative rate technique at pressures around 4700 torr between 1095-1240 K. The primary dissociation processes are 1,1 and 1,2 H2 elimination with ø1,1 ⋍ 0.75 and ø1,2 ⋍ 0.25, respectively. Subsequent decompositions of the primary process product, n-propylsilylene, to propylene and ethylene is complete even in the presence of excess butadiene. Possible mechanistic paths for these decompositions are discussed and an activation energy range of 30 ± 4 kcal is established for both processes. Induced decomposition via silylene chains accounts for 36-46% of the overall reaction in the uninhibited decomposition of n-propylsilane. The silylene chains are quenched in excess butadiene, and studies under maximum inhibition give overall decomposition kinetics of, log k(nPrSiD3, s-1) = 15.26-65,300 ± 1950 cal/2.303. Computer modeling results of the overall reaction both in the absence and presence of butadiene are also presented and shown to be in acceptable agreement with the experimental observations.

Notes: Trifluoro-t-butoxy radicals have been generated by reacting fluorine with 2-trifluoromethyl propan-2-ol: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \dot F} + {\rm CF}_3 {\rm C}({\rm OH})({\rm CH}_3)_2 \to {\rm HF} + {\rm CF}_3 {\rm C}({\rm \dot O})({\rm CH}_3)_2 $$\end{document} Over the temperature range 361-600 K the trifluoro-t-butoxy radical decomposes exclusively by loss of the —CF3 group [reaction (-2)] rather than by loss of —CH3 group [reaction (-1)]: The limits of detectability of the product CF3COCH3, by gas-chromatographic analysis, place a lower limit on the ratio k-2/k-1 of ca. 75. The implications of these results in relation to the reverse radical addition reactions to the carbonyl group are discussed along with the thermochemistry of the reactions.

Notes: The gas-phase reaction of CF3 with HCN has been examined over a wide conversion range using CF3I as a thermal and photolytic source of radicals. Quantitative and qualitative results show a significant increase of the specific rate constant for the hydrogen abstraction reaction relative to CF3 recombination when reaction is carried out under ultraviolet irradiation. This “extra” formation of the reaction product, CF3H, has been assigned to the participation of iodine in this system through the formation of a (I-HCN) intermediate. Arrhenius parameters obtained for the addition mechanism of I to HCN do not seem to conform to a single reaction step, on the contrary, they correspond to a more complex reaction scheme.

Notes: The kinetics and equilibria of the reaction: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Br} + {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} {\rm OCH}_{\rm 2} {\rm CH}_{\rm 3} {\rm}\mathop {{\rm \rightleftharpoons}}\limits^{\rm 1} {\rm HBr} + {\rm CH}_{\rm 3} {\rm CHOCH}_{\rm 2} {\rm CH}_{\rm 3} $$\end{document} have been studied in the temperature range 298-333 K by using the very low pressure reactor (VLPR) technique. Combining the estimated entropy change of reaction (1), ΔS°1 = 8.1 ± 1.0 eu, with the measured ΔG°1, we find ΔH°1 = 4.2 ± 0.4 kcal/mol; ΔH°f(CH3CHOC2H5) = -20.2 kcal/mol, and DH° [Et OCH(Me)-H] = 91.7 ± 0.4 kcal/mol. We find: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_1 (1/{\rm mol s)} = 10.8(\pm 0.7) - (3.9 \pm 4.0)/\theta $$\end{document} where θ = 2.3 RT in kcal/mol. It has been shown that the reaction proceeds via a loose transition state and the “contact TS” model calculation gives a very good agreement with the observed value.

Notes: The reactions of some perfluoroalkyl radicals with carbon tetrachloride have been studied using the photolysis of the corresponding perfluoroalkyl iodide as the free radical source. The Arrhenius parameters, based on the value of 2.3 × 1013 cm3 mol-1 s-1 for the self-combination rate constant of all radicals are: TextReactionlog(A/cm3 mol-1 s-1)E/kcal mol-1CF3 + CCl412.811.3C2F5 + CCl412.811.6n-C3F7 + CCl412.912.0

Notes: The decomposition kinetics of ethylsilane under shock tube conditions (PT ca. 3100 torr, T ≃ 1080-1245 K), both in the absence and presence of silylene trapping agents (butadiene and acetylene) are reported. Arrhenius parameters under maximum butadiene inhibition are: log k(C2H5SiH3) = 15.14-64,769 ± 1433 cal/2.303 RT; log k(C2H5SiD3) = 15.29-66,206 ± 1414/2.303 RT. The uninhibited reaction is subject to silylene induced decomposition (63% lowest T -- 24% highest T). Major reaction products are ethylene and hydrogen, consistent with two dominant primary dissociation reactions: C2H5SiD3 → C2H5SiD + D2, φ ≃ 0.66; C2H5SiD3 → CH3CH = SiD2 + HD, φ ≃ 0.30. Minor products suggest several other less important primary processes: alkane elimination, φ ≃0.02, and free-radical production via simple bond fission, φ ≃0.02. An upper limit for the activation energy of the decomposition, C2H5SiH → C2H4 + SiH2, of E 〈 30 ± 4 kcal is established, and speculations on the mechanism of this decomposition (concerted or stepwise) with conclusions in favor of the stepwise path are made. Computer modeling studies for the reaction both in the absence and presence of butadiene are shown to be in good agreement with the experimental observations.

Notes: The photooxidation of formaldehyde in CH2O—O2, oxygen-lean mixtures was studied in the temperature range 298-378 K. H2 and CO formation and the loss of O2 proceed by a chain mechanism, which between 328 and 378 K follows the previously suggested kinetics [1] with one modification. The reaction HO2 + CH2O ⇄ HO2CH2O (5) is now assumed to be reversible and ΔH5° is estimated to be between 14 and 19 kcal/mol. The relative yields of the chain formed H2 and CO and of the consumed O2 remained constant over the entire temperature range indicating that the relative efficiencies of the HO reactions: HO + CH2O → H2O HCO† (7), HO + CH2O → H2O + HCO (8) and HO + CH2O → HOCH2O (9) are temperature independent.

Notes: The effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N2, and SF6 over the pressure range 200-730 torr. All experiments were at room temperature. The method involved laser-induced fluorescence to measure steady-state OH concentrations in the 184.9 nm photolysis of H2O-CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O2 on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N2 and SF6, but not for Ar, within an experimental error of about 10%. The pressure effect for N2 was somewhat lower than previous literature reports, being about 40% at 730 torr. For SF6 a factor of two enhancement was seen at 730 torr. In each case it was found that O2 had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.

Notes: The extinction coefficients and the decay kinetics of I2-. and (SCN)2-⋅ have been characterized over the 15-90°C-temperature range. The extinction coefficients of I2-⋅ at 385 and 725 nm were determined to be 10,000 and 2560M-1 cm-1, respectively, based on the extinction coefficient of (SCN)2-⋅ at 475 nm being equal to 7600M-1 cm-1. At these three wavelengths, all extinction coefficients were constant over the temperature range studied. The rate of decay of both I2-⋅ and (SCN)2-⋅ was found to be a function of I- and SCN- concentration, respectively, as well as temperature.

Notes: The pyrolysis kinetics of several ethyl esters with polar substituents at the acyl carbon have been studied in the temperature range of 319.8-400.0°C and pressure range of 50.5-178.0 torr. These eliminations are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are given by the Arrhenius equations: for ethyl glycolate, log k1 (s-1) = (12.75 ± 0.30) - (201.4 ± 3.8) kJ/mol/2.303RT; for ethyl cyanoacetate, log k1 (s-1) = (12.19 ± 0.18) - (191.8 ± 2.1) kJ/mol/2.303RT; for ethyl dichloroacetate, log k1 (s-1) = (12.62 ± 0.36) - (193.9 ± 4.3) kJ/mol/2.303RT; for ethyl trichloroacetate, log k1 (s-1) = (12.27 ± 0.09) - (185.1 ± 1.0) kJ/mol/2.303RT. The results of the present work together with those reported recently in the literature give an approximate linear correlation when plotting log k/k0 vs. σ* values (ρ* = 0.315 ± 0.004, r = 0.976, and intercept = 0.032 ± 0.006 at 400°C). This linear relationship indicates that the polar substituents affect the rate of elimination by electronic factors. The greater the electronegative nature of the polar substituent, the faster is the pyrolysis rate. The alkyl substituents yield, within experimental error, similar values in rates which makes difficult an adequate assessment of their real influence.

Notes: Mathematical modeling was used for the kinetics of gas-phase propane oxidation at 586, 613, and 658 K and pressures 172 and 250 torr. The reaction mechanism involving branching by decay of the peracetyl peroxy radical, and oxygen-containing products formed on decay of the RO4 radical is discussed. Fair agreement between calculated and experimental results on the kinetics and accumulation rates of reaction products was obtained.

Notes: The termolecular rate constant for the reaction Cl + NO2 + M has been measured over the temperature range 264 to 417 K and at pressure 1 to 7 torr in a discharge flow system using atomic chlorine resonance fluorescence at 140 nm to monitor the decay of Cl in an excess of NO2. The results are\documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm He}} = 9.4{\rm } \times {\rm }10^{ - 31} \left({\frac{T}{{300}}} \right)^{ - 2.0 \pm 0.05} {\rm cm}^6 {\rm s}^{ - {\rm 1}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm N}2} = (14.8{\rm } \pm {\rm }1.4){\rm } \times {\rm 10}^{ - 31} {\rm cm}^6 {\rm s}^{ - 1}$\end{document} at 296 K where error limits represent one standard deviation. The systematic error of k1 measurements is estimated to be about 15%. Using a static photolysis system coupled with the FTIR spectrophotometer the branching ratio for the formation of the two possible isomers was found to be ClONO(≥75%) and CINO2(≤25%) in good agreement with previous measurements.

Notes: By photolyzing azomethane over the temperature range 331-491 K in the presence of trifluoroacetone the kinetics of the addition reaction (1), ĊH3 + CF3COCH3 → CF3C(Ȯ)(CH3)2 have been studied. Detailed analyses have shown that the principal product of the adduct radical, CF3C(Ȯ)(CH3)2, is CH3COCH3 from reaction (-2), CF3C(Ȯ)(CH3)2 → CH3COCH3 + ĊF3. The rate constant of the addition reaction has been determined to be k1(dm3/mol s) = (4.5 ± 1.4) × 107 exp(-(3370 ± 120)/T) over the temperature range 331-491 K, based on the value k3 = 2.2 × 1010 dm3/mol s for the reaction (3), 2ĊH3 → C2H6. The results are discussed in relation to existing data for radical additions to groups.

Notes: A unique capillary die was designed which made possible the measurement of extrusion pressure at various locations along the capillary length. Entrance pressure drops, exit pressures, and other rheological characteristics were determined for the flow of poly(ethylene terephthalate) through this extrusion apparatus. The effect of die entrance angle, extrusion temperature, throughput rate and polymer molecular weight were considered. Two samples differing in molecular weight exhibited power-law behavior at shear rates below 1000s-1. The entrance pressure drops and exit pressures were observed to increase with increasing molecular weight; furthermore, at a specific temperature, both-increased with increasing shear rate. The values for entrance pressure drop obtained using Bagley analysis were consistently higher than those obtained from direct measurements.

Notes: The determination of charge storage and charge decay processes in polyethylene electrets by means of TSD techniques alone seems to be limited by deficiencies in resolving power and reproducibility. Therefore, in the present work, we describe a new differential technique which cancels the effects of parasitic currents and improves the reproducibility of the measurements. The dependence of the shape of thermograms on experimental poling conditions has been studied. The comparison of discharge currents from the differential technique and from the usual one has also been found to be an interesting means of investigating the charge decay processes.

Notes: Polythiophene and substituted polythiophene can be electrochemically generated as very adhesive thin films or as thick powdery deposits. The homogeneity of the thin films is very high, but it decreases when the film thickness is increased. Scanning electron microscopy shows that the nature of the dopant strongly influences the film morphology. Transmission electron microscopy reveals mainly a fibrillar structure, with a fibril diameter of 200 Å in the undoped state, and 800 Å in the doped conducting state.

Notes: X-ray studies on polymers with phenyl benzoate side groups separated from the main chain by spacer groups of various lengths have been performed. It was found that the dimensions of liquid-crystalline regions are 15-20 nm, and they contain four to six close-packed layers. Thermal changes in x-ray scattering are associated with the variation of sizes and concentration of liquid-crystalline regions determined by the mobility of the main chain.

Notes: Results of Krik, Bidstrup, Merrill, and Meyers on polydimethylsiloxane networks of high functionality φ yield values of the reduced force [f*] in the high-extension limit that are directly proportional to (vs/V) (1 - 2/φ) where vs/V is the number of effective chains in volume V. The contention that trapped entanglements contribute significantly to the modulus is refuted by adherence of the results to this proportionality down to the lowest degrees of interlinking. Features of the relationship of stress to strain that appear to be in conflict with current theory are attributable to crowding of chains about the junctions of high functionality and of large linear dimension in the networks investigated by these authors.

Notes: The far-infrared spectra of poly(styrene sulfonic acid) (PSSA) ionomer films containing alkaline and alkaline earth ions have been studied, and strong, broad bands, whose frequencies are cation dependent, have been observed and assigned to cation motion. The force field elements for cations vibrating at sulfonate-containing sites have been obtained for different models of the cation-motion vibration. The effects of hydration, dehydration, and thermal annealing are discussed in light of ion clustering in these materials.

Notes: The changes in the structure and morphology of a random copolymer containing 92 mol % glycolide units and 8 mol % lactide units as a function of in vitro hydrolysis have been studied. A number of techniques, such as wide-angle x-ray diffraction, small-angle x-ray scattering, density measurements, infrared spectroscopy, and viscometry were employed in this study. The results showed that the hydrolytic attack was initiated in the amorphous areas of the polymer. After 28 days in the in vitro medium most of the amorphous areas had been chemically converted to lower-molecular-weight species such as oligomers of poly(glycolide-co-lactide). These low-molecular-weight species become water solble and are removed rapidly after day 28. Thus the fiber takes on a Swiss cheese character as the amorphous matter is hydrolyzed and eventually dissolved. As hydrolysis proceeds further, the crystalline areas of the polymer are attacked and eventually removed from the fiber by solubilization. The resulting voids in the fiber are eventually filled by a “collapse” of the structure. The role of the amorphous areas of the polymer in controlling the tensile strength of the suture is discussed.

Notes: It has been found that flow-induced coalescence occurs at a very rapid rate during the mixing of polymeric fluids. Furthermore, the rheological properties of the dispersed and continuous phases, as well as the nature of the flow field used in their blending, can greatly influence this coalescence. The significance of these findings is that in the development of a mixing scheme to obtain a desired morphology with minimum expenditure of time or energy, attention is usually focused only on the particle breakup aspects of the blending process. The competing coalescence can, however, be accelerated by the same conditions often employed to facilitate particle breakup (e.g., higher shear rates, reduced dispersed-phase viscosity).A better understanding of the mechanism for coalescence of viscoelastic fluids is clearly required. In this manner optimal blending of immiscible polymers can be achieved with respect to both the nature of the final material and the ease with which it is obtained.

Notes: Broad-line NMR measurements have been carried out on solid amylose, pullulan, and dextran in order to shed light upon the relations between different modes of linkage of glucose residues and physical properties. Rotation of the methylol group attached to the C5 atom around the C5—C6 linkage and the libration of glucose residues around the α-1,6 linkage are suggested as the origins of the observed decrease of the second moment with increasing temperature.

Notes: Fourier-transform infrared (FTIR) studies of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends are presented. Both compatible (one-phase) and phase-separated blends were studied. In the case of compatible PS/PVME blends, there is strong evidence for molecular interactions. The interaction spectrum was obtained by digital subtraction techniques. In contrast, no interaction is detected for the phase-separated blends. In view of these results, molecular interactions must play a role in the compatibility of the two polymers. The merits of factor analysis and least-squares fit methods, as pertaining to our data, are also discussed.

Notes: Poly(ethylene terephthalate) (PET) (intrinsic viscosity 0.59) and cellulose (Whatman) are compatible in up to 7.5% (w/v) solutions in trifluoroacetic acid and in mixtures of trifluoroacetic acid and methylene chloride. Evaporation of the solutions yielded films that did not contain cellulose per se, but rather partial esters of cellulose and trifluoroacetic acid. Clear films were cast from these solutions with compositions of 100/0, 75/25, 50/50, 25/75, and 0/100 PET. cellulose (w/w). Infrared spectra and DSC measurements indicate specific polymer-polymer interaction although two Tg were observed. Hydrolysis of the trifluoroacetate films to blends of PET and regenerated cellulose was accomplished by suspending the films in water at the boil. Infrared spectra indicate no interaction between the two polymers, although the films of the 50/50 and 25/75 PET. cellulose compositions were clear. The 25/75 composition, from its Tg and melting-point behavior appears to be a dispersion of very small-particle PET in a cellulose matrix. The 75/25 composition became opalescent during the hydrolysis and may be a dispersion of large-particle cellulose in a PET matrix. The regenerated cellulose appears to be a mixture of cellulose II and IV polymorphs.

Notes: Wide-line NMR has been used in an investigation of noncrystalline (amorphous) regions in oriented semicrystalline polymers. Nylon 6 was chosen as a model material. The tie-chain length distribution function, the fraction of tie chains in the total number of chains in the crystallite cross section, and the relative number of taut tie chains have been determined. The data on the tie-chain length distribution are used in discussing specific features of vitrification of the amorphous regions in oriented polymers and in prediction macroscopic mechanical properties.

Notes: The crystallization of highly oriented homopolymer melts (or glasses) is modeled. It is shown that in such cases heat flow controls the kinetics and microstructure of the transforming material. The situation is modeled similarly to the growth of a thermal dendrite, with the inclusion of large and variable concentrations of defects in the fibrillar crystals. Expressions relating the undercooling, growth velocity, filament tip radius, and defect concentration to a normalized tensile force are derived. Example predictions for the case of isotactic polystyrene are given.

Notes: Phase diagrams of low-molecular-weight polyethylene (M = 1000, 2000, 6500, 16,000) and polyethylene (M ≈ 1,000) after fuming nitric acid treatment have been determined from 20 to 300°C up to pressures of about 10 kbar. The fractions with molecular weights 1000 and 2000 do not exhibit the hexagonal phase, but the others do. Effects of molecular weight and fuming nitric acid treatment on the phase diagrams are discussed in terms of the entropy of the melt.

Notes: Single-crystal x-ray diffraction analysis is performed on a model compound (bisurethane of diphenylmethane-4-monoisocyanate and butanediol-1,4) for the thermoplastic polyurethane (TPU) hard segment formed from diphenylmethane-4,4′-diisocyanate and butanediol-1,4. The resulting structure is compared to structure models of corresponding TPU hard segments, especially to the structure proposed by Blackwell and Ross. Our results confirm this structure model showing a planar zigzag of the (CH2)4 group and planar hydrogen bonding between the urethane groups of adjacent molecules. X-ray diffraction analyses of polymeric TPU hard segments and of TPU elastomers with noncrystallizing soft segments lead to a revision of the dimensions of the proposed lattice cell, resulting in a more plausible value of 1.3226g/cm3 for the crystal density.

Notes: Attention is called to an early observation of Case II diffusion kinetics during penetration of a liquid into a uniaxially prestretched polymer film along the axis of stretching. Application of a previously developed transverse differential swelling stress model to these experimental conditions is described. It is shown that the model can predict Case II diffusion kinetics in a physically meaningful manner and will also explain the transition of the kinetics of the above system into normal or hindered diffusion regimes as either the degree of stretching or its direction relative to that of penetration is changed.

Notes: The temperature, strain-rate, and pressure dependences of the yield stress have been determined for two polyethylene homopolymers of differing molecular weights and for a polyethylene copolymer. Samples were prepared by slowly cooling from the melt, and also by quenching in order to assess the effects of morphology on the yield behavior. The data have been analyzed on the basis of two Eyring processes acting in parallel. Comparison of all data sets reveals the existence in general of three distinct activated processes each with its own temperature, strain-rate, and pressure dependences. The relative contribution of each process is dependent on the molecular weight, morphology, etc. Also discussed is the relation of these three yield processes to the well-known loss processes of linear viscoelasticity.

Notes: The effect of diluents and temperature on segmental motion in poly(vinyl acetate) was investigated by both NMR and ESR spectroscopy. Three classes of diluents were studied: chloroform, a thermodynamically good solvent; water, a poor solvent which slightly swells the polymer and lowers its glass transition temperature; and decane, a nonsolvent so poor it does not appear to swell the polymer nor lower the calorimetric glass transition temperature. At all temperatures investigated each type of diluent increased the segmental motion of the polymer over that of the bulk sample. Under the conditions studied, 13C and 2H NMR and nitroxide spin-label ESR data gave similar views of segmental motion of the polymer, indicating that in this amorphous polymer the segmental motion of the polymer may be safely inferred from spin-label data.

Notes: Poly(tetramethyl-p-silphenylene siloxane) crystal mats initially prepared from benzene/methanol (2:1 v/v), when annealed in small amounts of solvent undergo considerable thickening in the chain direction. When the crystals are annealed above their formation temperature, their physical properties change rapidly at first before reaching an asymptotic limit commensurate with annealing time and type of solvent. Changes in melting temperature, heat of fusion, small-angle x-ray spacing, and wide-angle x-ray scattering patterns have been monitored for three solvents of varying solvent power, ranging from very good to extremely poor. Upon solution annealing, the original crystals mats equilibrate to more stable dimensions compatible with their environment. The activation energy of crystal thickening in contact with a liquid is estimated to be about an order of magnitude lower than that deduced from dry annealing data. It appears that the crystal surface and the crystalline core of the crystals comprising the mats must participate in the measured severalfold increase in long period noted after annealing. The lower surface (or interfacial) energy of the liquid annealed mats compared to isothermally melt-crystallized polymer of similar molecular weight has a direct bearing on the polymer morphology and crystallinity.

Notes: Previous interpretations of gas transport data in crosslinked networks have been hindered by an inability to accurately control and evaluate the network parameters. We have recently prepared a series of model networks by reacting poly(propylene glycol) with a triisocyanate crosslinking agent. The poly(propylene glycol)s had narrow molecular weight distributions and average molecular weights between 425 and 3000, so the resulting networks had uniform average molecular weights between crosslinks. Hydrogen and carbon monoxide permeabilities in membranes formed from these networks increase with decreasing crosslink density. These results indicate increased cooperative molecular motions in the networks with longer average chain lengths between crosslinks. Increasing the average molecular weight between crosslinks also reduces the discrimination between these two gases so that the separation factors decrease. For networks prepared from mixtures of poly(propylene glycol)s with different molecular weights the gas permeabilities (but not the separation factors) depend on the molecular weight distribution.

Notes: The effects of poling temperature on piezoelectricity and its thermal stability were investigated on the basis of the thermal molecular motion associated with the crystalline region. This was done by using a film of highly oriented poly(vinylidene fluoride) containing form-I crystals. The film was prepared by a zone-drawing apparatus of the forced-quenching type. The piezoelectric stress constant e31 is a monotonically increasing function of the poling temperature which becomes steeper above ca. 320 K and again at ca. 400 K. The degree of orientation of the crystal b axis generated by poling also increases more steeply with poling temperature above ca. 320 K and again at 400 K. These temperatures correspond, respectively, to the crystalline dispersion temperature at 11 Hz, designated as αc, and the initiation temperature Tpm of large-scale molecular motion corresponding to premelting of form-I crystals. Thus the effect of poling temperature on piezoelectricity closely reflects the moleculer motion in form-I crystals. The annealing temperature T'a at which e31 decreases to 70% of that of unannealed sample by annealing a poled sample increases with the poling temperature and again this increase is steeper above poling temperatures of ca. 320 K and ca. 400 K. Thus the decay of piezoelectricity depends on both the αc temperature and Tpm.

Notes: The probability W(t) that a given number t of segments of an infinite chain lie within a given sphere can be expressed in terms of the single-pass length probability and the probability of reentrance into the sphere. The problem of calculating these two probabilities is equivalent to that of a diffusing particle exiting or entering the sphere after a given time, when the surface of the sphere is an absorbing wall. It is shown that the boundary condition, c = 0, usually applied to an absorbing surface cannot be used for the present purpose. The boundary condition used instead is the so-called radiation condition ∂c/∂z = kc; it is shown that when k approaches infinity the final answer for W(t), which is given in the form of an infinite series, approaches the correct limit. In this same limit the ratio 〈t〉2/〈t〉2 has the value 2.4

Notes: A new chlorination mechanism has been suggested for polyethylene crystals. Based on electron microsocopy and infrared spectroscopy of chlorinated high-density polyethylene single crystals, it is proposed that beyond the initial chlorination of the lamellae surfaces, which accounts for only 2-3% chlorine uptake, the reaction proceeds through the lamellar side faces from the periphery inward. Thus at intermediate degrees of chlorination two major phases coexist: the undamaged interior regions of the lamellae and the surrounding chlorinated material. This mechanism differs from that of oxidative degradation, and also from the generally Accepted mechanism of chlorination. Rather than proceeding through the reacted fold surface into the crystalline core, it is proposed that the direction of chemical attack is prependicular to that suggested previously. This mechanism probably describes any chemically nondestructive attack on the crystalline regions of polymers in general.

Notes: The ion etching technique has been applied to a morphological study of mechanically blended polypropylene (PP) with high-density polyethylene (HDPE). Samples blended to PP/HDPE compositions of 65/35 and 85/15 by weight were highly drawn and then heat treated for 30 min at selected temperatures up to 163°C. When these samples are carefully ion-etched several features are observed in electron micrographs, namely (i) crosshatched, and (ii) twisted or layered textured inclusions of HDPE crystals within arrays of lamellalike PP crystals situated perpendicular to the direction of drawing. X-ray diffraction measurements of the drawn samples heat treated in the range 145-163°C for 30 min shows that oriented HDPE crystallizes with b-axis orientation along the drawing direction. Supporting evidence is obtained from electron diffraction measurements. The molecular weight of the HDPE component is a major factor in the b-axis-oriented growth of HDPE crystals in PP/HDPE blends.

Notes: The mechanical and optical behavior in the dry and swollen states of loosely crosslinked epoxy networks prepared from the diglycidyl ether of bisphenol A, phenylglycidyl ether, and 4,4′-diaminodiphenylmethane was investigated, and the weight fraction of sol in the networks was determined. The crosslinking density was controlled by an excess of diamine and by the fraction of monoepoxide. The reaction proceeded to almost full conversion of epoxy groups. With increasing content of monoepoxide or with increasing excess of diamine, the main transition region is shifted to lower temperatures. The dependence of the viscoelastic modulus on temperature and the optical behavior indicate that the networks are homogeneous. In all cases, the sol fraction is adequately described by the theory of branching processes (cf. Part I). The equilibrium modulus related to the dry state is the same irrespective of whether it is obtained by measurements in the dry or swollen state. The mechanical behavior in the rubbery state can be described by the theory of phantom networks with fully suppressed fluctuations of crosslinking (front factor A = 1) or by the theory of phantom networks with fully released fluctuations of crosslinks (front factor) A = fe-2/fe] and contribution of trapped entanglements of the Langley-Graessley type (cf. Part I). In the analysis of the equilibrium behavior, it is advantegeous to use the plot of superimposed dependences of Ge on the gel fraction, which considerably reduces the effect of experimental inaccuracy in determination of composition and degree of conversion.

Notes: An experimental study has been made to specify how the time-temperature superposition and the linear viscoelastic characteristics vary with the degree of crosslinking for a broad class of noncrystalline peroxide-cured EPDM networks. A new, very sensitive method is applied to determine the horizontal and vertical shift functions in an independent way. All uncrosslinked samples are thermoelasticoviscously simple with horizontal shift functions aT of the WLF type and vertical shift functions almost independent of temperature, in agreement with recent theoretical understanding. Upon crosslinking, these materials become thermoviscoelastically complex networks, but superposition can still be accomplished by assuming different temperature dependences for the relaxational strength and the equilibrium modulus. The aT functions can be taken independent of the degree of crosslinking. The vertical shift functions bT for the relaxational strength vary with the degree of crosslinking between theoretical predictions for uncrosslinked and perfectly crosslinked EPDM networks. The equilibrium moduli of the lightly cured networks decreases with increasing temperature, which is ascribed to the presence of interchain associations between ethylene sequences in the trans state. Upon further crosslinking, these effects gradually vanish and eventually the networks can be described as viscoelastically simple with an energy elastic contribution due to the ethylene trans-gauche transitions. The linear viscoelastic characteristics, namely the storage and loss moduli and compliances and phase-angle master curves and the relaxation and retardation spectra are discussed as a function of the degree of crosslinking. A sol/gel analysis and equilibrium swelling measurements complete the experimental characterization of three familes of five EPDM networks each.

Notes: Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0-700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ3 of 54 K, and θ1 of 250 K, and a full set of group vibrations. Cv to Cp conversion was possible with a Nernst-Lindemann constant of A = 1.6 × 10-3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔCp of 9.4 J/K mol. The room-temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high-temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds.

Notes: Quantitative Fourier-transform infrared (FTIR) measurements of frequency shifts Δν and absorbance profile asymmetry are reported for various polypropylene samples as a function of uniaxial stress σ. Generally, it was found that the frequency shift coefficient αχ, defined by Δν = αχσ, depended on stress rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, draw ratio, λ, molecular orientation f, tensile modulus E, and annealing conditions. With annealing, αχ decreased with increasing shrinkage in the case of highly oriented isotactic PP. The αχ values for the “helix bands” were less affected than those for the “liquid bands.” With increasing \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, generally αχ increased to an apparent asymptotic limit. With increasing λ, f, or E, αχ also increased from αχ ≃ 0 for λ = 1 (spherulitic) to maximum values for highly oriented isotactic PP. The observed variations in αχ can be interpreted in terms of the changes in the peak position and shape of the nonuniform molecular stress distribution. Analogous behavior with x-ray diffraction peaks obtained for polymers under stress is discussed.

Notes: The sorption and diffusion of toluene vapor at 30°C in polypropylene with draw ratios from 1 to 18 have been studied. Drawing leads to the transformation of the initially spherulitic material into the fibrous structure, with many taut tie molecules lying mainly on the outer boundary of the microfibrils. The free volume and hence the sorption sites are thereby reduced, and the microfibrils become less and permeable as the draw ratio increases. As a result, the equilibrium concentration and the zero-concentration diffusion coefficient drop by factors of 4 and 30, respectively. The diffusion coefficient increases exponentially with toluene concentration but the concentration dependence becomes weaker with increasing draw ratio, indicating that the severely constrained chain segments in the drawn samples have much less freedom to mix with penetrant molecules. Annealing relaxes the tie molecules and thus restores the sorption and diffusion properties to values corresponding to completely relaxed amorphous component, i.e., to values even higher than those of the undrawn but quenched material.

Notes: X-ray analyses of methylene-bis(4)phenyl isocynate(MDI)/diol/poly(tetramethylene adipate) polyurethane elastomers prepared using hexanediol (HDO), butanediol (BDO), and propanediol (PDO) point to the development of a second crystalline structure in the hard segments as a result of thermal elongation and annealing. The HDO polymer crystallizes initially in the fully extended conformation, but a second crystal structure, a contracted form, develops with stretching and annealing at 130°C. In contrast, the BDO and PDO polymers crystallize initially in contracted conformation, but fully extended forms develop as a result of elongation and annealing. Only a contracted conformation has been seen so far in hard segments prepared using ethylene glycol (EDO) as the chain extender. These results correlate very well with DSC data for the same polymers. The development of the new crystal structures is accompanied by the appearance of new hard-segment melting peaks in the DSC traces. For the HDO polymer, the new peak for the contracted form appears at a higher temperature than that for the original extended form; for the BDO and PDO polymers the new peaks for the extended forms appear at lower temperatures than those for the contracted forms. Only a single peak is seen for the EDO polymer, for which only one crystal structure has been detected for the hard segments. These results indicate that the development of polymorphic crystal structures must be taken into account in interpreting the multiple melting phenomena seen for the hard domains in polyurethane elastomers.

Notes: A linear chain model is used to calculate the thermal expansivities of polymer crystals from room temperature down to liquid-helium temperature. Because of restraint by strong covalent forces, vibrations along the chains give a negligible contribution. Vibrations transverse to the chains cause the length projected along the chain direction to decrease. The expansivity along the chain direction, αc∥ is therefore negative, and has temperature dependence characterized by the low Debye temperature of transverse vibrations. These vibrations, through a cubic term in the interchain van der Waals potential, also cause a positive expansivity, αc⊥ perpendicular to the chain direction. The theoretical predictions for αc∥ and αc⊥ agree quite well with experimental data over the wide temperature range under consideration.

Notes: Sorption isotherms for pure CO2 and pure CH4 in Kapton H® polymide films at 60°C are reported for pressures up to 20 atm and are analyzed in terms of the dual-mode sorption model. An experimental scheme for the measurement of steady-state permeabilities of both pure and mixed gas feeds is described. Permeabilities of Kapton to the individual components at 60°C are presented for a mixture comprised of 32.2% CO2 in CH4 as functions of feed pressure up to 590 psi (absolute). The permeabilities for the individual penetrants in the mixed feed are lower than the respective purecomponent values at the corresponding partial pressures. Furthermore, the permeabilities of both penetrants drop as the feed pressure is increased at constant composition. The dual-mobility transport model used to analyze the data postulates that the observed pressure and composition dependence of the permeabilities is due to competition between penetrants for a limited microvoid sorption capacity in the glassy polymer. It is demonstrated that in addition to flux depressions due to dual-mode effects, nonideality of the gas phase must be accounted for to explain the substantial flux depressions observed for the CO2/CH4 mixtured used in this study.

Notes: The morphology of isotropic films of poly[N,N'-bis(phenoxyphenyl)-pyromellitimide] was investigated by means of small-angle x-ray scattering. A significantly different morphology was found to develop in these films as compared to that in films possessing as in-plane molecular orientation. It was found that morphology could be described by a damped periodic modulation in the electron density characteristic of a chain segment aggregation. An increase in the initial imidization temperature resulted in an overall increase in the lateral packing of the chains and a reduction in the amplitude of the density modulation. Evidence was also found for segmental aggregation in the precursor polyamic acid which contained up to 35% solvent.

Notes: The newly arisen possibility of crystallizing polyethylene at supercoolings much higher than were achievable previously has enabled the study of crystallization to be extended in several directions. Thus, fold length can be followed down to previously inaccessibly low crystallization temperatures, in the present case with sharp fractions, demonstrating the essential independence of the fold length of molecular weight. In this context the thinnest isolated crystal reported so far was obtained (ca. 6 nm). The faceted nature of crystals grown at such low temperatures and high rates has been noted, and is in line with new conceptions of polymer crystal growth. A previous observation of exceptionally high crystal growth rate (ca. 2 m/s) has been supplemented by measurements over a range of crystallization temperatures and the results found to be in good agreement with the predicated regime III behavior in the least theory of Hoffman. Observations of epitaxy on mica, while broadly in line with those by Lovinger, were revealing in several respects. Among these the observation that the substrate can influence the fold length when the chains are parallel to the substrate plane remains unexplained and puzzling.

Notes: Uniaxial stretching and orientation of some linear flexible-chain polymers have been investigated. A functional relation has been found between the maximum recoverable deformation and the limiting extension of the macromolecules. These deformations are found to increase in direct proportion to the square root of the degree of polymerization and to decrease with increasing stiffness of the polymer chain.

Notes: Transient and steady-state rheological data are reported for several anionic polystyrene solutions in tritolylphosphate (1. 6 〈 cM/ρMc 〈 7). Here c is the concentration of the solution, M is the molecular weight, ρ the density of the undiluted polymer, and Mc the molecular weight between entanglements as determined from zero-shear viscosity. The polystyrene used had Mw = 410,000 and Mw/Mn 〈 1.06. Data are also given for solutions of polyisobutylene and poly(vinyl acetate) with larger Mw/Mn. The results give a critical strain γ′ ∝ c-1 such that linear viscoelastic behavior was obtained in a simple shear deformation with shear less than γ′. A simplified version of the constitutive equation of Bernstein, Kearsley, and Zapas is used with an empirical strain function F (γ) which contains γ′ as a parameter to discuss transient and steady-state behavior in terms of the distribution of relaxation (or retardation) times determined for linear viscoelastic responce. Features of the dependence of the steady-state viscosity ηk, recoverable compliance Rk, the first-normal stress function Nk(1) on shear rate k are discussed in terms of F (γ) and the distribution of relaxation times to conclude that the latter plays a dominant role in the behavior observed in the range of k usually studied. The results predict that the reduced functions ηk/η0, Rk/R0, and Nk(1)/N0(1) should depend on η0R0k, and that the functional form depends markedly on the distribution of relaxation times, at least in the range η0R0k 〈 102. Comparison with the mechanistic model of Doi and Edwards shows a similar F (γ) but substantial differences in the reduced functions caused by a very narrow distribution of relaxation times in the model.

Notes: The major objective of this work was to develop a simple and rapid technique to quantitatively measure the macromolecular chain orientation in polypropylene surfaces. A previously described experimental design employing attenuated total reflection spectroscopy near the critical angle was applied. The infrared dichroism of the 841- and 809-cm-1 bands of polypropylene was used to quantitatively determine a fractional orientation function of the macromolecular chains along the three major film axes (machine direction, transverse direction, and thickness or normal direction). The surface orientation of a set of polypropylene films uniaxially extended from 0 to 500% was determined using this technique. The variation of surface orientation, bulk crystallinity, and thickness with extension of these uniaxially extended films were compared. The surface orientation of an unoriented and several biaxially oriented polypropylene films was compared to the bulk orientation determined by a similar transmission infrared dichroism method. It was found that surface and bulk orientation were generally similar. It was shown that rather small orientations could be measured by the surface orientation method and that it was applicable to multilayer films and very thick samples, where the transmission method fails.

Notes: Infrared spectra in conjunction with calorimetric measurements have been used to follow the crystallization process and microstructural changes of poly(ethylene oxide) (PEO) in poly(ethylene oxide) and poly(methyl methacrylate) (PMMA) blends. We have given particular attention to compositions containing low PEO concentrations. The crystallization behavior and the resultant microstructures of PEO are strongly perturbed by the presence of PMMA. In addition, we found phase separation and trans sequences of PEO to be present, especially at low PEO concentrations.

Notes: We report polarized photon correlation measurements of bulk poly(phenylmethyl siloxane) (PPMS) with a molecular weight of about 2500 at different pressures from 1 to 1750 bar and temperatures between 269 and 308 K. In the Frequency range accessible by present-day digital correlators, the time correlation function can measure a slow q2-dependent diffusional process due to local concentration fluctuations and a fast α-mode structural relaxation process. The mean characteristic times of the two processes approach each other at low temperatures and high pressures, in contrast to the behavior of the α- and β-relaxation times. We should be cautious in relating the mean characteristic times for the structural relaxation process obtained by different experimental techniques, such as Brillouin scattering and photon correlation spectroscopy, because of the differnces in the probe emphasis and the extremely broad frequency distribution of such relaxation processes.

Notes: The kinetic network (KN) model discussed previously in the context of monodisperse and bimodal polymer systems is extended to polymers of arbitrary molecular weight distribution. A generalization is proposed for the flow-dependent entanglement loss term in the structure equation, replacing the shear rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} by a new variable \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \Gamma $\end{document} which reduces to\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} for simple shear and is more appropriate for elongational and other flows. New data are obtained on shear stress transients of many kinds, using a recently developed parallel-plate rheometer. These data and others on steady and transient flows of well-characterized polydisperse polymers in shear and in elongation are used to demonstrate that the KN model predictions are valid. Comparisons with predictions for monodisperse polymers having the same as Mw polydisperse systems show that transient behavior - especially stress overshoot - is particularly sensitive to details of the molecular weight distribution. Further possible improvements in the theory are suggested, and the relationship of the KN model to other recent network models is discussed. The KN model has greater data fitting capabilities, with fewer parameters, than any other model available at present.

Notes: The heat of fusion ΔHf of 66 nylon has been determined by use of the Clapeyron equation. Measurements of ΔHf and the unit-cell parameters on molding pellets show that this material contains the α2 crystal phase, which is less dense than the α1 phase obtained by crystallization from solution. The value of ΔHf-45-46 cal/g, is in good agreement with earlier reports.

Notes: The thermodynamic and structural properties of a series of hydrogenated polybutadienes, crystalized in the bulk and from dilute solution, have been investigated. These polymers are ethyl-branched ethylene copolymers with narrow molecular weight and composition distributions. Despite the fact that for both modes of crystallization these random-sequence copolymers display a lamellar crystalline habit, all of the independent physical chemical measurements are quantitatively consistent in indicating a relatively thin crystallite with a large amorphous disordered overlayer. This is seen to be a very general phenomenon for copolymer crystallization. The core thicknesses, determined from Raman LAM and from small-angle x-ray scattering, are in good agreement. Quantitatively consistent values of the degree of crystallinity are obtained from the density, enthalpy of fusion, Raman internal modes, Raman LAM, and small-angle x-ray scattering. It is significant that independent thermodynamic and structural methods give the same result.

Notes: Analytical expressions describing the kinetics of photoinitiated free-radical polymerization are derived for a variety of conditions. The effect of the exponential attenuation of intensity of light in the direction of incidence in the system is carefully accounted for in each case. An attempt is made to include the depletion of initiator due to its photolysis in the kinetic scheme. The marked difference between the polymerization kinetics in well-stirred and unstirred systems is shown by comparing them under limiting conditions. The variation of this difference with the optical density of the system is illustrated graphically. The influence of light absorption by components other than the photoinitiator (e.g., solvent, monomer) is examined. The order of the polymerization reaction with respect to initiator as determined by conventional kinetic experiments depends on the amount of light absorbed by components of the system other than the photoinitiator.

Notes: Fourier transform infrared (FTIR) studies of polystyrene (PS)/poly(vinyl methyl ether) (PVME) miscible blends as a function of temperature are presented. Below the lower critical solution temperature (LCST) little change is observed in the interaction spectrum obtained via digital subtraction techniques. Once above the LCST, the magnitude of the interaction spectrum decreases as a result of the phase separation process. Comparison of the behavior of the ether C—O stretching band in the reference PVME and in the blends has yielded a lower limit estimate for the interaction energy of about 0.15 kcal/mol.

Notes: Regression rates as functions of air flow rates and oxygen content of the oxidant gas as well as the distance of the polymer surface from the top of the reaction vessel have been investigated for poly(methyl methacrylate), poly(α-methyl-styrene), a polymide, and isotactic polypropylene. The results are discussed from the standpoint of reaction kinetics, considering regression rates and energies of activation for diffusion and degradation.

Notes: The radius of gyration Rg, the hydrodynamic radius Rh, and the intrinsic viscosity [η] have been measured for polystyrene in cyclohexane (at the θ temperature and 44.5°C), 2-butanone (at 30°C), and toluene (at 30°C) in the molecular weight range 2.38 × 105 ≤ Mw ≤ 5.47 × 106 to elucidate the excluded-volume effects on dynamical behavior in dilute polymer solutions in the crossover region from θ to good-solvent conditions. The results are compared with theoretical predictions of current thermal blob theories and the Pade approximant theory of Tanaka. It is found that the ratio of Rh/Rg decreases with an increase in the excluded-volume effect, following the prediction of the simple blob theory, but that its magnitude is about 15% higher than the theoretical value. Experimental variation of [η] with Rh and/or Rg lies in between predictions of the scaling law and the Pade approximant. The concentration dependence of the diffusion coefficient is also compared with predictions of current theories.

Notes: The published data on the mechanical response of a set of samples prepared from a single batch of polyisobutylene have been examined and three relaxation/retardation processes have been characterized in the temperature region above the glass transition temperature. It is shown that the time/frequency dependences can be explained in terms of the cooperative theory of relaxation/retardation. It is also shown that the values of the fractional power-law indices of relaxation/retardation, which are a characteristic feature of the cooperative approach, are independent of the technique used in their observation.

Notes: The stress-optical behavior of an unswollen elastomeric network of poly(3-methyltetrahydrofuran) was measured for elongation ratios a in the range 1.182-1.549, at several temperatures between 20 and 60°C. No evidence of strain-induced crystallization was found; moreover, the dependence of birefringence Δn on true stress f/A was linear in the interval of α investigated. Values of Δa ranged from 2.4 to 2.8 in units of 10-24 cm3, in the temperature range studied, with a temperature coefficient 3.1 × 10-3 K-1. Theoretical calculations carried out with the rotational-isomeric-state model gave values of Δa noticeably smaller than the experimental results; however, a small increase in the backbone valence angles θ improved the theoretical result of Δa without worsening that of the dipole ratio. Analysis of the Δa results seems to corroborate the conclusion obtained through the study of dipole moments concerning the preference for nucleophilic attack on the less hindered α carbon in the monomer. Theoretical and experimental values of the temperature coefficient of Δa were in clear disagreement; a qualitative explanation for this discrepancy is discussed.

Notes: A connection is presented between the Jones-Stockmayer solution to the three-bond-jump equation for local motion and the new correlation function developed by Hall and Helfand. Both correlation functions are based on a diffusional picture for cooperative local motions which allows for the development of a relationship between them. Numerical fits of the Hall-Helfand function to the Jones-Stockmayer function are also given for both the time and frequency domain; these numerical fits are consistent with the analyses of NMR data by both models. The fits and the analyses set a likely range for converting the correlation time of the three-bond jump to the correlation time for the cooperative transitions in the Hall-Helfand model.

Notes: Melting behavior of an experimental Halar film, a predominantly alternating 1:1 copolymer of ethylene (E) and chlorotrifluoroethylene (CTFE), has been studied. Differential scanning calorimetry (DSC) reveals single or double melting peaks, depending upon the thermal history. The lower-temperature melting peak Tm1 is produced only by the thermal treatment and shows a strong dependence on annealing time and temperature. On the basis of the DSC and x-ray data it can be suggested that Tm1 represents the melting of relatively small crystallites formed upon annealing. The higher-temperature melting peak Tm2 is always shown at 238°C. (Note: the specification for commercial Halar product is 240°C. The slightly lower melting temperature reported in this study is probably due to the fact that we are dealing with an experimental melt-processed material.) On the basis of the heating rate study we propose that Halar crystallizes with stable crystals (Tm2 = 238°C) regardless of the crystallization conditions, i.e., quenching, slow cooling, or even annealing. Crystals of Halar have a heat of fusion of approximately 35 cal/g or 146 kJ/kg. Detailed analysis of the melting behavior of Halar is presented.

Notes: The thermally induced cholesteric to isotropic transition of lyotropic polybenzylglutamate liquid crystals in six solvent combinations was examined optically. The solvents chosen for study support both low and high pitch values, positive and negative pitch temperature coefficients, and polypeptide denaturation. The biphasic zone below the clearing temperature is broad and solvent dependent. Unusual large-scale phase separations and solution morphologies occur in some solvents. No evidence was found for pretransitional chiral orientational ordering near the clearing point in the high-temperature isotropic phase.

Notes: The phenomenon of surface scattering of electromagnetic waves by single or multiple layers of films is reviewed and a special treatment for the total reflection of x rays is developed. This theory is applied to the analysis of the surface scattering observed in small-angle x-ray scattering (SAXS) studies of two-phase matter in polymers having lamella stacks or a flat interfacial boundary structure. Important features of this vector theory are the ability to calculate the surface scattering invariant, the absolute scattering intensity, and the surface roughness, which gives rise to dispersion of specular reflection from perfectly smooth surfaces. By considering the interfacial surface roughness of polystyrene crazes, the surface scattering spectrum is calculated theoretically and compared with some experimental results. Also the theory is presented in such a way as to compare surface scattering with volume scattering; i.e., both two- and three-dimensional scattering events can be simultaneously treated. This provides a new basis for quantitative analysis of crazes in polystyrene.