摘要:

AbstractThe criteria of livingness, as applied to anionic polymerizations, are discussed. A number of restrictions have to be taken into consideration, if anionic polymerizations are to be applied to the synthesis of model polymers, Several examples of synthesis of tailor‐made polymers via anionic polymerization are presented, namely end‐functionalizations, chain extensions, end‐to‐end cyclizations, block copolymer synthesis, grafting processes, methods to make star polymers. In each case the reliability of the methods is discussed tho

ISSN:0258-0322    

DOI:10.1002/masy.19930670103

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractRecent advances in the anionic ring‐opening polymerization (AROP), including covalent (pseudoanionic) polymerization, are reviewed. Thermodynamics, kinetics, and mechanisms of AROP are discussed, covering mostly polymerization of oxiranes, lactones and cyclic siloxanes as monomers. The following general problems of AROP are discussed: anionic polymerizability, thermodynamics ‐ particularly of the monomers exhibiting low ring strain, chemistry of initiation, structures and reactivity of active species. New phenomena, particularly polymerization with reversibly aggregating species are analyzed in more detail. Chain transfer to polymer ‐ the major side reaction ‐ is analyzed quantitatively, by introducing the selectivity parameter β, expressed by the ratiokp/ktr. This parameter has been determined for the anionic and pseudoanionic polymerization of ϵ‐c

ISSN:0258-0322    

DOI:10.1002/masy.19930670104

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe stereochemistry of anionic polymerization of vinyl monomers: CH2=C(R)C(Y)=X where X and Y are O, N or C and R = H or alkyl is discussed in terms of a: the geometry of the ‐CH2C‐(R)C(Y)=X intermediate existing as E‐ or Z‐isomers; b: the interactions of cation (Li, Na, etc.) with the anion and coordinating groups on the penultimate or antepenultimate asymmetric carbon. The E/Z ratio appears to be determined directly by the s‐trans/s‐cis approach of the monomer. The nature of the coordination of the counter ion is considerably more complicated and is discusse

ISSN:0258-0322    

DOI:10.1002/masy.19930670105

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe concept of a living polymerization is critically discussed. A system ranking various classes of “livingness” is proposed, and the importance of determining the real values of ktr/kpand kt/kpratios is expounded. New living systems, including carbocationic polymerization and group transfer polymerization of acrylates are compared with classic ionic systems. The mechanism of propagation and the nature of the true active species are similar in both new and classic polymerizations. The role of various components which improve the “livingness” of the polymerizations is discussed and explained by dynamic equilibration between dormant and active species and suppression of side re

ISSN:0258-0322    

DOI:10.1002/masy.19930670106

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractSome problems in ionic polymerization are reviewed. The existence of a variety of species participating in ionic polymerizations is stressed and the distinction between the growing, dormant, and dead polymers emphasized. An example of a kind of polymer that does not fit any of these three classes is given suggesting that still other examples might be discovered in the future.

ISSN:0258-0322    

DOI:10.1002/masy.19930670107

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe side reactions in the anionic polymerization of (meth)acrylates initiated by organolithium compounds raise the question about favorable interactions between organolithium and carbonyl compounds in general and in this polymerization reaction. The results of several crystal structures of lithium(sodium) (ester) enolates without or with other molecules clearly demonstrate the favorable formation of homo‐ and mixed aggregates, respectively. It is also shown how different gegenions (ZnBr+, R4N+, etc.) influence the overall structure and the structure of the anio

ISSN:0258-0322    

DOI:10.1002/masy.19930670108

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThis article summarizes possibilities of tailoring polyacrylates and polymethacrylates prepared by anionic polymerization initiated with combined (mixed) initiators especially those containing alkali metaltert‐alkoxides as stabilizing additives. First part gives a short overview of side reactions in anionic polymerization of polar vinyl monomers and the ways of solving the problem. Second part is devoted to the anionic polymerization of acrylic and methacrylic esters initiated with mixed initiators. Examples of synthetic methods are given for the preparation of special polymeric products based on acrylates, and the necessity of using different polymerization conditions for individual acrylic esters is demonstrated with respect to branching of the ester alkyl grou

ISSN:0258-0322    

DOI:10.1002/masy.19930670109

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractLiving anionic polymerization of methacrylic esters initiated with aluminum porphyrins (1) was found to be dramatically accelerated (e.g., 46 000 times) upon addition of bulky Lewis acids such as alkylaluminum diphenolates (3). Under appropriate conditions, a narrow MWD poly(methyl methacrylate) with Mn exceeding a million could be synthesized. The key conception of this high speed living polymerization is the coexistence of nucleophile (2) and Lewis acid (3) realized by steric repulsion.

ISSN:0258-0322    

DOI:10.1002/masy.19930670110

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractKinetic studies on the isotactic‐specific living polymerization of methyl methacrylate witht‐C4H9MgBr were carried out in toluene at −78°C and the kinetic orders with respect to the monomer and initiator were found to be unity. Propagation rate in the early stage of polymerization and the initiation rate were studied by kinetic measurement and analysis of oligomer distribution. The rate constants for the propagation of the unimer (k1), dimer (k2), and trimer anions (k3) were found to be in the following order;k1>>k2>k3.13C NMR spectra of the oligomer anions indicated the coordination of penultimate and antepenultimate ester groups to Mg counterion. Possible mechanism for stereoregulation in the early stage of polymerization was dis

ISSN:0258-0322    

DOI:10.1002/masy.19930670111

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractLiving and highly isotactic poly(methyl methacrylate) (PMMA) anion (M̄n= 2.5 × 103) prepared witht‐C4H9MgBr as an initiator was protonated with phenol in toluene at −78°C. The reaction was stereospecific towardmesoaddition, and themeso/racemoratio at the chain‐end of the resultant polymer was 89/11. Addition of 1,4‐dioxane to the living isotactic PMMA anion in toluene at −78°C remarkably reduced the viscosity of the system, and protonation of the PMMA anion with phenol in the presence of 1,4‐dioxane enhanced themeso‐specificity to 94%. On the other hand, the protonation reaction of the living syndiotactic PMMA anion (M̄n= 2.5 × 103), which was generated byt‐C4H9Li/(n‐C4H9)3Al in toluene at −93°C, witht‐butanol was found to be 97%racemo‐specific. These highly stereospecific protonation reactions of the stereoregular PMMA anions were in contrast to the protonation of the anions with methanol or benzyl alcohol which

ISSN:0258-0322    

DOI:10.1002/masy.19930670112

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY