摘要:

AbstractDifferent aspects of radical polymerization have been investigated in the author&s laboratory.1) Radical oligomerization has been studied by GC‐MS and some kinetic parameters obtained in this way (chain transfer and reinitiation constants, reactivity ratios) compared with the results of classical experiments.2) Star‐shaped polymers have been obtained by using a series of polyfunctional chain transfer agents; the experimental results agree very well with the theoretical expectations. 3) A reexamination of the copolymerization equation showed that the steady‐state assumption is not a necessary condition for the kinetic derivation and that all approaches are conceptually equivalent. 4) The structure and the 2D NMR spectra of hemiisotactic polypropylene obtained by radical inclusion polymerization are disc

ISSN:0258-0322    

DOI:10.1002/masy.19910470103

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA series of macrocyclic poly(2‐vinylpyridine)&s were synthesized by high dilution (∼10−5M) coupling of the two‐ended living precursor dianions with 1, 2‐ and 1, 4‐bis‐(bromomethyl)benzene (1, 2‐ or 1, 4‐DBX). SEC measurements indicate that the macrocycles contain less than 5% linear precursor and that the hydrodynamic size of the macrocycles is substantially (∼30%) less than that of the linear precursor. At very low MW, the sizes of macrocyclic and linear polymers differ less, particularly for the case of the 1, 2‐DBX product. Viscometry measurements in THF of linear and macrocyclic polymers also indicated substantial size differences of linear and macrocyclic P2VP.The values of the glass transition temperature (Tg) for both the 1, 2‐ and 1, 4‐DBX macrocycles were found to increase with decreasing MW as qualitatively predicted by entropy calculations. Thus, as the degree of polymerization decreases, the macrocyclic chains become conformationally stiffer and this is reflected by higher Tgvalues. The differences in Tgbetween linear and macrocyclic P2VP are quite large (∼40K) around a DP of 40 and decrease to values of a few degrees at a DP of around 200. These differences are diagnostically useful in estimating the linear content of the ma

ISSN:0258-0322    

DOI:10.1002/masy.19910470104

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

Abstract1, 1‐Diphenylethylene is not capable of being homopolymerized, neither by radical nor by anionic mechanism. This is due to both electronical and sterical reasons. 1, 1‐Diphenylethylene, however, is eligible to electron transfer reactions to yield the radical anion which subsequently upon combination reaction forms the dimeric dianion. On the other hand, 1, 1‐diphenylethylene may be subjected to the nucleophilic addition of strong nucleophiles such as carbanions, e.g., butyllithium or polystyryllithium. Upon this reaction, a carbanion is formed the nucleophilicity of which is significantly reduced as compared with that of the starting carbanion. Molecules containing the characteristic group of 1, 1‐diphenylethylene twice, in analogous reactions, may be subjected to polycombination reactions upon electron transfer. The polymers exhibit cyclic or linear structure depending on the molecular structure of the starting divinylidene compound. Upon reaction with carbanionic species, biscarbanions are formed which may be used as initiators for the anionic polymerization of suitable monomers. A variety of divinylidene compounds and their specific features are pr

ISSN:0258-0322    

DOI:10.1002/masy.19910470105

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe most important recent development in cationic polymerizations is the emergence of living polymerizations leading to a variety of new potentially useful well‐defined macromolecules under conventional laboratory conditions. Three requirements have to coexist for living carbocationic polymerization to occur: Controlled initiation controlled chain‐transferless propagation and controlled (quasiliving) termination. The first part of this presentation will briefly discuss the road to these three key requirements. The second part will concern practical consequences and select systems. The synthesis of narrow‐molecular‐weight‐distribution (M̄w/M̄n= 1.1 ‐ 1.3) tert‐chlorine telechelic polyisobutylenes over a wide molecular weight range (M̄nfrom ∼1000 to ∼125, 000 g/mole) will be outlined together with recent work on aromatic olefins, e.g., styrene, tert‐butylstyrene and p‐chlorostyrene. These developments led to the combination of these living systems for the synthesis of block copolymers by sequential monomer addition. Tri‐ or higher block copolymers comprising glassy outer segments and rubbery inner segments, for example, poly(styrene‐b‐isobutylene‐b‐styrene, poly(p‐chlorostyrene‐b‐isobutylene‐b‐p‐chlorostyrene), have been prepared. These new thermoplastic elastomers exhibit phase‐separated microstructures and an interesti

ISSN:0258-0322    

DOI:10.1002/masy.19910470106

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper focuses on two recent topics in living cationic polymerization of vinyl monomers,i.e.,(a) Development of new initiating systems: RCOOH/Lewis acid for vinyl ethers; CH3CH(C6H5)Cl/SnCl4/nBu4NCl for styrene.(b) Synthesis of shape‐controlled poly(vinyl ethers): Tri‐armed star polymers; Multi‐armed spherical polymers.For the RCOOH‐based systems, a generalized concept of living cationic polymerization was discussed on the basis of the effects of the counteranions (or R) and Lewis acids (ZnCl2and EtAlCl2). The CH3CH(C6H5)Cl‐based system permitted a truly living cationic polymerization of styrene. The tri‐ and multi‐armed poly(vinyl ethers) included new amphiphilic polymers of unique topology, solubility, etc., all of which were prepared by living cationic p

ISSN:0258-0322    

DOI:10.1002/masy.19910470107

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractWith homogenous catalysts on the basis of chiral metallocenes and methylaluminoxane it has become possible to polymerize cyclic olefins like cyclobutene, cyclopentene or norbornene. No ring opening reaction occurs. The crystalline polycycloalkenes show extremly high melting points between 400 and 600°C. Copolymers of cyclopentene with propene are amorphous. They have a low molecular weight and glass transition point. On the other hand the glass transition temperature of norbornene/ethene copolymers exceeds 130°C. These copolymers could be used as materials for optical discs and fiber

ISSN:0258-0322    

DOI:10.1002/masy.19910470108

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractAn approach of the special problems observed in copolymerization with Ziegler‐Natta heterogeneous catalysts is given on the basis of linear low‐density polyethylene synthesis in gas phase reaction. The reaction is controlled by chemistry and not by diffusion. The ethylene‐l‐butene copolymerization reactivity computed from the kinetic study varies with the copolymer composition, and this is due to the fact that the comonomer acts as a ligand of the active centers. The reactivities computed from NMR analysis are also not really reliable as the copolymer is a mixture of copolymers with different compo

ISSN:0258-0322    

DOI:10.1002/masy.19910470109

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractSoluble LC polymers were synthesized with the aim to approach molecular reinforcement. Chemical modification results in a decrease of the crystallinity and an increase of the solubility. Substitution of the amide hydrogen in poly(4‐aminobenzoic acid) by a methyl group reduces the stiffness of the polymer very much, and as a result no lyotropic solutions are obtained. Poly(p‐phenylene terephthalate) with substituents on the hydroquinone or on both monomer units were synthesized. With one phenylalkyl group in the repeating unit the polyesters are crystalline with melting points>300°C. With two substituents the polymers form in many cases amorphous anisotropic glasses at room temperature. 2‐Biphenyl is the most effective substituent with regard to increase of solubility. These polyesters form isotropic solutions in chloroform. Isotropic films obtained from these solutions become anisotropic on heating above the glass transition temperature. Films of polyester/polycarbonate blends show additivity of E‐modulus with respect to both c

ISSN:0258-0322    

DOI:10.1002/masy.19910470110

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractPolymerization of ε‐caprolactone initiated with dialkylaluminum alkoxides is a living system; formation of macrocyclics is fully depressed. Polymerization initiated with diethylaluminum alkoxide and diisobutylaluminum alkoxide proceeds on monomeric (deaggregated) active species, reversibly aggregating into trimers for the former and into dimers for the latter initiator. Kinetic treatment of this system allowed to determine simultaneously the aggregation‐deaggregation equilibrium constant and the rate constant of propagation. Propagation most probably proceeds with insertion (pseudoanionically). Application of amines, complexing the growing species, allowed to break down the aggregates; polymerization became firstorder in initiator. Only secondary amines complexed strongly enough with growing species, the tertiary ones did not affect polymerization, at least up to the ratio 2:1 ([amine]/[initiator]o). Rate constants of propagation in all of the studiedosystems, whether aggregated or not, have been found to be the same and equal to 0, 04 1·mol−1·s−1at 25° in THF solvent. This value is approx. 102times lower than for ion‐pairs at these conditions. Moreover, rate constants are almost the same for the growing species …‐OAl(C2H5)2and …‐OAl(i‐C4H9)2, although aggregation is very much influenced by the s

ISSN:0258-0322    

DOI:10.1002/masy.19910470111

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe polymerization of tetrahydrofuran under a living form allows quantitative functionalisation as well as the formation of copolymers. Cyclic acetal polymerization is more complex but through the “Activated‐Monomer Mechanism” approach, it is possible to prepare telechelic polymers as well as block and graft copolymers with particular emphasis concerning amphiphilic

ISSN:0258-0322    

DOI:10.1002/masy.19910470112

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY