摘要:

AbstractThe recent realization that 1,2‐dichloroethyl branches occur in poly(vinyl chloride) (PVC) has now led to a full description of the chemical consequences of head‐to‐head addition during the free‐radical polymerization of vinyl chloride (VC). A kinetic analysis of the relevant reaction scheme is developed here and then verified with the aid of literature values for the branch concentrations of PVC samples prepared by polymerization at subsaturation VC pressures. The analysis allows the following conclusions to be drawn: (1) Kinetically free chlorine atoms are not formed from polymeric ‐CHCl‐CH‐CH2Cl or ‐CH2‐CH‐CHCl‐CH2Cl radicals. Loss of chlorine from these radicals results exclusively, instead, from β scission reactions that transfer chlorine directly to the monomer and are kinetically second‐order, overall. (2) The monomer transfer constant that pertains to the transfer occurring after head‐to‐head addition is, indeed, a true constant that is independent of the concentration of VC. (3) In conventional bulk or suspension VC polymerizations, the rates of the propagation reactions are not controlled by diffusion, even at conversions ofca.90%. (4) A second type of monomer transfer process probably is responsible for the reductions in polymer molecular weight that result from polymerization at subsaturation VC pressures. This transfer pathway involves the inter‐ and/or intramolecular abstraction of methylene hydrogen from the polymer by the ordinary head‐to‐tail macroradicals. The resultant β‐chloroalkyl radicals then

ISSN:0258-0322    

DOI:10.1002/masy.19930700103

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractSynthetic polymer gels are known to exist in two phases, swollen and collapsed. Volume transition occurs between the phases either continuously or discontinuously. More than two phases are found in gels consisting of copolymers of randomly distributed positively and negatively charged groups. They are characterized by distinct degrees of swelling; the gel can take one of a set of swelling values, but none of the intermediate values. The number of phases depends on the composition of positively and negatively charged monomers, and decreases from a maximum of seven at a particular composition to one at pure cationic or anionic gel compositions. In these gels, polymer segments interact with each other through attractive or repulsive electrostatic interactions and through hydrogen bonding. The combination of these forces appears to result in multiple phases. The multiple phases seem to have important biological implications. The finding demonstrates that a polymer system can take a stable state other than swollen and collapsed phases, which was known only for proteins. Studying them may lead us to the principle with which linear chains of amino acids form unique and stable structures, a question of protein folding, and how they create marvellous functions such as molecular recognition, catalysis, and motion.

ISSN:0258-0322    

DOI:10.1002/masy.19930700104

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA question about broken rods and worms concerning the dimensional characteristics of poly(alkyl isocyanates) led to the discovery of an extreme sensitivity of this polymer class to tiny chiral perturbations. There is a cooperative source of this phenomenon and statistical thermodynamic methods allow quantitative expression to the forces at work. From this effort we could answer the original question and also extend these ideas into the area of lyotropic liquid crystals where the interplay of macromolecular and supramolecular helicity seems to play by the same rules.

ISSN:0258-0322    

DOI:10.1002/masy.19930700105

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe concept of the equilibration of surface states in contact is examined by the measurement of the contact electrification and separation currents, and applied to the investigation of the evolution of the surface state due to a change of contacting medium (from air to water) by following the surface concentration (by ESCA) of labeling atoms (F), which were incorporated by a low temperature plasma (of CF4), as a function of water immersion time and temperature. The kinetic rate constants for such changes of surface configuration follow a typical Arrhenius plot, which shows a conspicuous break at a surface transition temperature Ts. Ts's observed against air coincide with the glass transition temperature Tg's of the corresponding polymers. Ts's observed against water, however, are found to be independent of Tgand consistently near 15 °C, which coincides with the major Drost‐Hansen temperature of vicinal water. The surface state of water is the dominant factor in this ca

ISSN:0258-0322    

DOI:10.1002/masy.19930700106

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractPolyester‐block‐polyethers with rigid thermotropic polyarylate blocks are prepared and studied. Rigid polyarylates are poly(1,5‐pentanediyl 4,4′‐biphenyl‐dicarboxylate) or poly(1,5‐pentanediyl 4,4′‐trans‐stilbenedicarboxylate). Flexible blocks are oligo(oxytetramethylene)s (M̄n= 620 or 2030). The block copolymers are characterized by1H and13C NMR spectroscopies. The use of 500 MHz1H NMR permits their complete structural analysis showing that they contain a cyclic oligomer. SEC, polarizing microscopy and X‐ray studies show that their mesophase is smectic. Their viscoelastic properties are compared to those of some aromatic poly

ISSN:0258-0322    

DOI:10.1002/masy.19930700107

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractAs a novel methodology for the preparation of organoboron polymers, this paper describes “hydroboration polymerization” and “haloboration polymerization”. A polyaddition between diene andtert‐hexylborane (thexylborane) produced a polymer consisting of C‐B bonds in the main chain. The resulting organoboron polymers can be regarded as a polymer homologue of trialkylborane and can be expected as a novel type of reactive polymers. For example, the reaction of organoboron polymer with carbon monoxide followed by the oxidative treatment produced a polyalcohol by the migration of C‐B bonds. Similarly, the reaction with potassium cyanide produced a polyketone. On the other hand, hydroboration polymerization of dicyano compounds such as isophthalonitrile with t‐butylborane produced an air‐stable boron‐containing polymer (polycyclodiborazane) having B‐N four‐membered rings via dimerization of iminoborane species. In haloboration polymerization, i.e., a polyaddition between diacetylene and boron tribromide, a linear poly(organoboron halide) was obtained. This polymer still has B‐Br bonds in its structure and was used not only as a novel reactive polymer but also

ISSN:0258-0322    

DOI:10.1002/masy.19930700108

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractHighly isotactic and highly syndiotactic living polymerizations of alkyl methacrylates were carried out in toluene at low temperatures byt‐C4H9MgBr andt‐C4H9Li‐R3A1, respectively. These living polymerizations enabled us to prepare highly stereoregular block and random copolymers of methacrylates with narrow molecular weight distributions. Reaction of ethylene glycol dimethacrylate with isotactic PMMA anion gave a highly branched star polymer. Syndiotactic PMMA star polymer was prepared by similar method. Stereoregular PMMA macromonomers with styrene and methacryloyl functions were prepared by using the stereospecific living polymerizations and polymerized by radical and anionic mechanisms. It was found that isotactic PMMA formed stereocomplexes with various types of syndiotactic polymethacrylates when treated under certain conditions. The complexes showed melting points which differ in a wide range of temperature. Isotactic and syndiotactic MMA oligomers without molecular weight distribution were isolated by supercritical fluid chromatography up to 29‐mer and charac

ISSN:0258-0322    

DOI:10.1002/masy.19930700109

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractInitiation of anionic polymerisation by means of enolate ions has many advantages. It has been applied to the synthesis of macromolecules with specific structures, e.g. graft and block polymers, and H‐polymers. Its application to dispersion polymerisation is also reporte

ISSN:0258-0322    

DOI:10.1002/masy.19930700110

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractGroup transfer polymerization (GTP)aof acrylic monomers is mediated by a trialkylsilyl‐capped growing chain end. It operates at room temperature and above and permits a high degree of molecular architecture control. Block, comb, graft, star, and loop polymers are readily synthesized. It appears that GTP is an associative process under mild nucleophilic catalysis and a dissociative process under strong nucleophilic catalysi

ISSN:0258-0322    

DOI:10.1002/masy.19930700111

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractSingle crystals, suitable for electron microscopy and diffraction, have been grown from the quiescent and sheared “liquid crystal” state and solution for several random terpolymer polyesters having a nearly equimolar amount of a flexible segment dicarboxylate (4–7 CH2), oxybenzoate and dioxyphenyl. In all cases, in thin films and on free surfaces, folded chain lamellae are observed. High temperature electron diffraction has permitted characterization of the transition behavior and structure of the liquid crystal state. Permanganate etching permitted characterization of the interior of molded, extruded or spun samples; in these cases extended chain lamellae are observed. The results suggest chain folding in the nematic state at least in the thin films and on surfaces, with chain folding also possible in the bulk followed by chain extension by “sliding”

ISSN:0258-0322    

DOI:10.1002/masy.19930700112

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY