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  • 1990-1994  (7)
  • Polymer and Materials Science  (7)
  • Inorganic Chemistry
  • Physics
  • Theoretical, Physical and Computational Chemistry
  • 1
    Digitale Medien
    Digitale Medien
    Cyclization versus polymerization in phase transfer catalyzed polytioetherification (1990)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 191 (1990), S. 71-79 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Some unexpected results were observed in the phase transfer of catalyzed (PTC) (two phase, aqueous-organic) polymerization of α,ω-dibromoalkanes with sodium sulfide. Alkane dielectrophiles containing fewer than six methylene units give rise to large, and sometimes quantitative, amounts of cyclic thioethers. These cyclic sulfides are formed under “polymerization” conditions and can be minimized by using only the monomer as the organic phase. Alkane dielectrophiles containing more than six methylene units yield only polymer. When a comonomer system composed of a 1:1 mixture of 1,4-dibromobutane (DBB) and 1,8-dibromooctane (DBO) is employed, the resulting copolymer's molecular weight and polydispersity are vastly improved compared to the corresponding homopolymerizations. Microstructurally, this copolymer is formed by complete consumption of DBO and partial incorporation of DBB. The remaining DBB forms tetrahydrothiophene (THT). These two odd and seemingly conflicting results could not be explained by “normal” or “inverse” PTC extraction mechanisms. Support of this new mechanism is given in the PTC polymerization of DBO with sodium sulfide in the presence of a catalytic amount of THT. The resulting polymer is of very high molecular weight and narrow polydispersity; it also does not contain tetramethylene sequences. Using this new mechanism, all results suggest the participation of cyclic sulfides either facilitates cyclic formation or enhance polymer reactivity as controlled by the length of the alkane dielectrophile.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1990.021910105
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  • 2
    Digitale Medien
    Digitale Medien
    Bimechanistic phase transfer catalyzed polythioetherification (1990)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 191 (1990), S. 3157-3161 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Relative concentrations of catalysts, sulfide catalyst structure, and organic phase monomer concentration were studied for the bimechanistic phase transfer catalyzed (BPTC) polymerization of aqueous sodium sulfide with 1,8-dibromooctane (DBO). BPTC is a new phase transfer mechanism which combines the effects of normal phase transfer with “inverse” phase transfer catalyzed reactions. Two catalysts are used: an ammonium salt and a cyclic or acyclic sulfide. With hexadecyltrimethylammonium chloride (CTMAC) and tetrahydrothiophene (THT), the optimum catalyst concentrations were found to be 10 mol-% and 5 mol-%, respectively, per DBO, but each was independent of the other. Diluting the monomer with o-dichlorobenzene did not significantly alter the mechanism's profile, but expectedly lowered obtainable molecular weight. Of five sulfide catalysts examined, pentamethylene sulfide and dimethyl sulfide were the best, producing the highest molecular weight polyaliphatic sulfides with polydispersities M̄w/M̄n of ca. 1,3.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1990.021911234
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  • 3
    Digitale Medien
    Digitale Medien
    Hydrophobicity scale for proteins based on inverse temperature transitions (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 1243-1250 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In general, proteins fold with hydrophobia residues buried, away from water. Reversible protein folding due to hydrophobia interactions results from inverse temperature transitions where folding occurs on raising the temperature. Because homoiothermic animals constitute an infinite heat reservoir, it is the transition temperature, Tt, not the endothermic heat of the transition, that determines the hydrophobically folded state of polypeptides at body temperature. Reported here is a new hydrophobicity scale based on the values of Tt for each amino acid residue as a guest in a natural repeating peptide sequence, the high polymers of which exhibit reversible inverse temperature transitions. Significantly, a number of ways have been demonstrated for changing Tt such that reversibly lowering Tt, from above to below physiological temperature becomes a means of isothermally and reversibly driving hydrophobic folding. Accordingly, controlling Tt, becomes a mechanism whereby proteins can be induced to carry out isothermal free energy transduction. © 1992 John Wiley & Sons, Inc.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360320913
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  • 4
    Digitale Medien
    Digitale Medien
    Prediction of microstructures for polydisperse block copolymers, using continuous thermodynamics (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 1379-1407 
    Details
    ISSN: 0887-6266
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A generalization of an earlier theory (Leary-Henderson-Williams) developed for microphase separation in monodisperse block copolymers is made for copolymers having moderate degrees of polydispersity and illustrated for the Schultz molecular weight distribution (MWD). First, an explicit study is made of molecular weight (M) effects for monodisperse poly (styrene-butadiene) diblock (SB) and triblock (SBS) copolymers. For a fixed temperature, it is shown how the critical molecular weight (Mc) - above which the copolymer is phase-separated at equilibrium  - varies with molecular composition (φS, volume fraction of S component) for both molecular architectures. Also predicted are the microstructural parameters ΔT(M) and f(M) - interphase thickness and volume fraction, respectively - and the high-M limiting functions ΔT ∝ Mα2, f ∝ Mα3, D ∝ Mα4 (D is domain repeat distance) and Ts ∝ Mα5 (Ts is separation temperature). Then, for polydisperse systems in the range 1 ≲ p ≲ 3 ( where \[ P = \bar M_w /\bar M_n \]) corresponding predictions at constant \[ \bar M_n \] are made after identifying the mixture free-energy-minimum state with a weight average of the free energy minima of each fraction of the MWD. Calculations are made specifically for φS = 0.50 and Ts = 298 K. It is shown that, even when \[ \bar M_n 〈 M_c \], polydispersity can induce microphase separation if p is sufficiently large. Good success is obtained in comparisons of D predictions with data on blends of two polydisperse diblock samples.
    Zusätzliches Material: 22 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/polb.1990.090280812
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  • 5
    Digitale Medien
    Digitale Medien
    XPS surface studies of injection-molded poly(phenylene ether)/nylon 6,6 and poly(phenylene ether)/HIPS blends (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 46 (1992), S. 1915-1925 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The surface compositions of a series of poly(phenylene ether)/nylon 6,6 blends (PPE/PA), and PPE/HIPS blends, prepared by melt compounding and injection molding, have been quantitatively measured using XPS. For PPE/PA blends, the surface is dominated by the PA component for blends containing more than 25 wt % PA in the bulk. The enrichment of the PA component, which is actually the component of highest surface free energy, is rationalized in terms of the bulk morphology that consists of PPE domains in a PA continuous phase. Blends prepared by reactive extrusion processes, which form compatibilizing PPE/PA copolymers, show a decrease in surface PA enrichment with increasing copolymer content in the final blend. PPE/HIPS blends have a surface composition equal to the formulated value over the entire composition range, for both molded and solvent cast blends. The addition of 5% PVME to a 60/40 PPE/HIPS blend results in a molded surface containing 35-40 wt % PVME. © 1992 John Wiley & Sons, Inc.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1992.070461104
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  • 6
    Digitale Medien
    Digitale Medien
    Static SIMS study of miscible blends of polystyrene and poly(vinyl methyl ether) (1990)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 15 (1990), S. 388-391 
    Details
    ISSN: 0142-2421
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: Static secondary ion mass spectroscopy (SSIMS) is applied to study the surface of the miscible polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend. The blend surface is enriched with PVME and the enrichment is shown to depend on the composition and molecular weight of the blend constituents. A semi-quantitative analysis of SSIMS intensities to obtain surface compositions gives good qualitative agreement with previous x-ray photoelectron spectroscopy (XPS) results.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/sia.740150608
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  • 7
    Digitale Medien
    Digitale Medien
    XPS and static SIMS studies of copoly(ether-esters) containing mixed polyether soft blocks (1994)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 21 (1994), S. 553-559 
    Details
    ISSN: 0142-2421
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: The surface compositions for a series of copoly(ether-esters) are determined from XPS and static SIMS measurements. The copolymers consist of a polybutylene terephthalate (PBT) hard block and a mixed soft block of two of the following polyethers - poly(propylene glycol) (PPG), poly(tetramethylene) oxide (PTMO) and poly(ethylene oxide) (PEO). The surfaces of all the copolymers are enriched in the total polyether soft blocks. Quantification of XPS intensities shows the presence of both polyethers at the surface of these mixed soft-block copolymers, in relative amounts close to the bulk formulations. In the static SIMS measurements, direct observation of characteristic fragment ions related to the specific polyethers confirms their presence and relative abundance in the surface.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/sia.740210807
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