ISSN:0022-233X    

DOI:10.1080/00222338908052029

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0022-233X    

DOI:10.1080/00222338908052030

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0022-233X    

DOI:10.1080/00222338908052031

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Several books have been published on the history of Polymer Science [1–5], and most of the post-1899 history parallels the lifetime of Dr. Maurits Dekker, who was born in Holland on March 18, 1899.

ISSN:0022-233X    

DOI:10.1080/00222338908052032

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Apparently no definitive experiments have ever been reported which could be defined as asymmetric autocatalysis. This paper discusses the design of several experiments which might lead to asymmetric autocatalytic reactions. The implications of this novel type of asymmetric synthesis are evaluated.

ISSN:0022-233X    

DOI:10.1080/00222338908052033

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Lithium diisopropylamide (LDA), in the presence of diisopropylamine (DPA), initiates the polymerization of 1,4-, or 1,3-divinylbenzene (DVB) to form a soluble poly(divinylbenzene). Initiation was confirmed to take place by addition of an alkylamino group to the DVB molecule. The population of the triad tacticity of the soluble poly(DVB) suggests the steric course of the polymerization reaction to proceed according to Bernoullian statistics with respect to the diad placements,mandr. The chain-transfer reaction was found to take place through proton transfer from DPA to the growing chain end. A kinetic study of the reaction between lithium alkylamide and poly(DVB) was carried out for comparison with some other styrene derivatives. The second-order rate constant (k) of the reaction between lithium diethylamide and the vinyl group of poly(DVB) was 1.19 × 10−3L·mol−1·s−1, which is only about one-fiftieth of that for 1,4-DVB. LDA was found to metalate the methyl group of 4-methylstyrene to form 4-vinylbenzyllithium without any side reaction. This carbanion has the structure of 10π-conjugation and is stable in the reaction system for more than 30 min. The vinylbenzyl anion is regarded as a model for the growing end of poly(DVB). On the basis of these results, the reason for formation of soluble poly(DVB) in the LDA-induced DVB polymerization is summarized as follows: (i) Relatively short life time of the growing carbanion owing to chain transfer by DPA; (ii) lower reactivity of the pendent vinyl groups of the soluble poly(DVB) compared with those of DVB monomer; and (iii) lowered reactivity of the growing carbanion, which has a stabilized 10π-conjugation.

ISSN:0022-233X    

DOI:10.1080/00222338908052034

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Polychloral was prepared in which the optical activity arose exclusively from macromolecular asymmetry (i.e., helical conformation). Strong chiral initiators used at 0.5 mol% concentration gave optically active polychloral. Maximum values of optical rotations for polychloral samples were obtained with the following initiators: lithium methyl (+)-hydroxidemandelate [α]D25= +3600°, lithium methyl (-)-hydroxide-mandelate [α]D25= -4670°. A technique was developed to measure reliably the optical rotation of polychloral samples in film form.

ISSN:0022-233X    

DOI:10.1080/00222338908052035

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Chloral polymerizations initiated with weak chiral initiators, used at 0.5 mol% concentration, gave optically active polychloral. Maximum rotations of the various polychloral samples, measured in film gorm, depended on the initiator as follows: tetramethylammonium (+)-O-acetylmandelate [α]D25= -1860°, tetramethylammonium (-)-O-acetylmandelate [α]D25= +1180°, tetramethylammonium (+)-α-methoxymandelate [α]D25= -190°, tetramethylammonium (-)-α-methoxymandelate [α]D25= +210°.

ISSN:0022-233X    

DOI:10.1080/00222338908052036

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The polymerization of isobutylene (IB) initiated by a variety of tertiary chloride/TiCl4or BC13systems can be very beneficially influenced by deliberately added electron-pair donors (ED's). ED's whose Gutmann's donor number is larger than ∼26, e.g., dimethylsulfoxide (DMSO) and dimethylacetamide (DMA), are most suitable to mediate numerous most desirable effects. Thus, in the presence of DMSO or DMA: (1) quasi-living polymerizations initiated by cumyl chloride (CumCl)/TiCl4or 2-chloro-2,4,4-trirnethylpentane (TMPCl)/TiCl4give rise to very narrow molecular weight distribution (MWD) polyisobutylene (PIB) (Mw/Mn= 1.1–1.2); (2) the CumCl/BCl3/IB inifer system becomes living and yields PIB with very narrow MWD; (3) the polymerization-inactive TMPCl/BCl3system becomes active and induces living IB polymerization to narrow-MWD product; (4) indanyl end-group formation, which may occur in the CumCl/BCl3orp-dicumyl chloride/BCl3, inifer systems, is eliminated. The effect of reaction conditions, e.g., polarity and [TiCl4]/([CumCl] + [DMSO]) ratio, on these polymerizations has been investigated. All the observations and effects can be explained by a reduction of cationicity of the polymerization-active species by ED's.

ISSN:0022-233X    

DOI:10.1080/00222338908052037

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The stereochemistry of alternating copolymers of styrene (ST) with maleic anhydride (MA) was examined by13C-NMR spectroscopy, and the stabilization energies and the most stable geometries of complexes and adducts between ST and MA were calculated by the PVCILO program and by INDO/1. The methine and carbonyl carbon atoms of the MA portion and the quaternary carbon atom of the ST portion reveal different stereochemistries due to various polymerization conditions, suggesting that the donor-acceptor complex may participate in the co-polymerization. The complex postulated according to the Diels-Alder geometry was more stable than that according to [2+2] cycloaddition geometry. It is believed that the stabilization energy is so great that the copolymerization occurs spontaneously via forming a donor-acceptor complex and adducts. The geometries of 1:1 adducts formed by endo and exo approaches in the Diels-Alder geometry mode were also calculated.

ISSN:0022-233X    

DOI:10.1080/00222338908052038

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor