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  • 1
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. The synthesis and characterization of novel stars, octa(polyisobutylenedimethylsiloxy)octasilesquioxane (T8 DPIB), consisting of eight polyisobutylene arms emanating from an octa(dimethylsiloxy)octasilsesquioxane (T8 D) core are described. The synthesis involves: 1) The synthesis of allyl-terminated polyisobutylene (PIB█01█) prearms, 2) The synthesis of octa(hydrodimethylsiloxy)octasilsesquioxane (T8 DH) precore and 3) Star formation by hydrosilation of PIB█01█ with T8 DH. Conditions for the precision synthesis and characterization of well-defined octa-arm stars are described.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Direct monitoring of cationic polymerization was accomplished by simultaneous measurement of the average dielectric constant, representing the dipoles, of the conductivity, produced by unpaired ions, and of the temperature, characteristic for reaction rate. The ionogenic equilibria during the living polymerization of isobutylene by 1, 3, 5-tris(2-methoxy-2-propyl)benzen/BCl3 in CH2Cl2 at-25°C were demonstrated. Temperature, resistance and capacitance were measured directly in the reaction mixture by a specially designed instrument. Both the conductivity and the average dielectric constant change characteristically during the living polymerization, indicating the presence and simultaneous change of unpaired ions and strongly polarized species. The differences between the AMI, and the aging technique were demonstrated and explained. In the latter case slow initiation was observed due to the methoxy-chlorine exchange caused by a reaction with BCl3. The applied direct monitoring method helps to understand the role of polarized and ionic species in polymerizations and related processes.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3341-3347 
    ISSN: 0887-624X
    Keywords: styrene polymerization ; p-chlorostyrene polymerization ; p-methylstyrene polymerization ; living carbocationic ; common ion effect ; kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of common anion producing salt, tetrabutylammonium chloride (n-Bu4NCl), on the livingness and kinetics of styrene (St), p-chlorostyrene (pClSt), and p-methylstyrene (pMeSt) polymerization initiated by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4 system has been investigated. Uncontrolled (conventional) carbocationic polymerization of St and p MeSt can be converted to living polymerization by the use of n-Bu4NCl. Under similar conditions the polymerization of p ClSt is living even in the absence of n-Bu4NCl, although the molecular weight distribution (MWD) of the polymer becomes narrower in the presence of this salt. The apparent rates of polymerizations decrease in the presence of n-Bu4NCl in proportion with the concentration of the salt. The rate of living polymerization of p ClSt is noticeably lower than that of St, while that of p MeSt is higher. The apparent rate constants, kpA, of these polymerizations have been determined, and the effects of the electron donating p Me- and electron withdrawing p Cl-substituents relative to the rate of St polymerization have been analyzed. [For part LXI, see J. Si and J. P. Kennedy, Polym. Bull., 33, 651 (1994)]. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3341-3347, 1997
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0887-624X
    Keywords: isobutylene polymerization ; living carbocationic ; conventional carbocationic ; proton trap ; mechanism ; kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of the proton trap, 2,6hyphen;di-tert-butylpyridine (DtBP), on the polymerization of isobutylene (IB) induced by the “HX”/TiCl4 (“HX” = protoic impurity) intiating system has been studied. Significantly, in the presence of a large (∼ 40 molar) excess of DtBP relative to “HX”, free proton-induced chain transfer-dominated conventional IB polymerization is converted to living polymerization. In the absence of the proton trap the kinetics are dominated by rapid proton-induced processs which overwhelm the relatively slower living polymerization. These investigations also led to a quantitative assessment of the concentration of initiating species: [“HX”] = 1.46 × 10-4 mol/L. The polymerizations are first-order in monomer and the apparent rate constants of propagation drop precipituously with increasing DtBP concentration until a constant low value is reached. The rate of formation of propagating living chains has been expressed quantitatively. Chain transfer is bimolecular and first order in monomer, and kinetic investigations led to a quantitative description of the effect of proton trap concentration on the apparent first order chain transfer constant. The results have been explained in terms of a simple mechanistic scheme. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. The synthesis and characterization of a novel star comprising eight allyl-terminated polyisobutylene (PIB) arms radiating from a calix[8]arene core is described. The synthesis was accomplished by a core-first method, by inducing the living polymerization of isobutylene (IB) by a suitably functionalized calix[8]arene initiator (1) in conjunction with BCl3-TiCl4 coinitiators, and terminating the growth of the living PIB⊕ arms by allyltrimethylsilane. The relative concentrations of BCl3 and TiCl4 are critical for the synthesis of well-defined 8-arm stars. Characterization of the products (which included triple detector GPC studies and 1H NMR spectroscopy) indicated quantitative allylation. A mechanism which summarizes the experimental observations is proposed.
    Type of Medium: Electronic Resource
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