摘要:

AbstractThe room temperature polymerization of methyl methacrylate (MMA) by the cesium or tetrabutylammonium salt of 9‐methylfluorenide proceeds in an uncontrolled fashion. To understand these results, we have studied the structure of the propagating chain‐ends using polymer microstructure and stopped‐flow FT‐IR spectroscopy of model compounds. Deprotonation of methyl isobutyrate with the cesium salt of 1,1,4,4‐tetraphenylbutane dianion afforded the corresponding cesium enolate (U=1645 cm−1). The deprotonation of methyl 2,2,4‐trimethyl‐4,6‐dicarbomethoxyhept‐6‐en‐1‐oate (the trimeric ester of MMA) was accompanied by a rapid (2–4 s) intramolecular cyclization. Comparison of group transfer polymerization (GTP) to anionic polymerization reveals that the counterion is important but probably not the sole mechanistic feature responsible for

ISSN:1022-1360    

DOI:10.1002/masy.19950950103

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA bimetallic aluminate complex (‘ate’ complex) is regarded to be the active species in the anionic polymerization of MMA in the presence of aluminium alkyls in toluene. The aluminate end group is supposed to be able to coordinate to the penultimate end group of the polymer chain. As a result, the rate of polymerization is significantly slower than for aluminium‐free polymerization. Excess aluminium alkyl (Al/Li>1) coordinates to the ester carbonyl groups of monomer and polymer, but there is no evidence for an activated monomer mechanism. To a small extent, the polymerization at −78°C is accompanied by side reactions (e.g. formation of vinyl ketones) but nevertheless it has a certain living c

ISSN:1022-1360    

DOI:10.1002/masy.19950950104

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe article presents a short overview of the controlled polymerization of (meth)acrylates assisted with Litert.butoxide as the stabilizer of active centres. The “living” homopolymerizations of 2‐ethylhexyl acrylate, butyl acrylate and allyl methacrylate, and the synthesis of fully‐acrylate block copolymers are given as examples. The reaction conditions always need to be tuned up with respect to the monomer. The stabilizing effect of lithium 3‐methylpentoxide‐3, which seems to be a highly efficient type of thetert.alkoxide stabilizing additive, is br

ISSN:1022-1360    

DOI:10.1002/masy.19950950105

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractMulti‐arm star polyisobutylenes (*‐(PIB)n) have been prepared by the “arm‐first” method. This synthesis was accomplished by adding various linking agents (“core builders”) such asp‐ andm‐divinylbenzene (DVB) andp‐ andm‐diisopropenylbenzene (DIB) to living PIB® charges and thus obtaining a crosslinked aromatic core holding together a corona of well‐defined arms. The products were characterized in terms of overall arm/core composition, molecular weight, and molecular weight distribution (M̄w/Mn). The effect of reaction conditions (time, [linking agent]/[PIB], arm molecular weight) on the kinetics of the star formation and star structure were investigated. The multi‐arm star nature of*‐(PIB)ns was proven directly by determining the molecular weight (by light scattering) of the intact products, selectively destroying the aromatic polyDVB (or polyDIB) core (“core‐destruction”), and finally determining the molecular weight of the surviving aliphatic PIB arms. The synthetic strategy, overall kinetics, and observations during the preparation of star‐PIBs were discussed. Among the critical parameters that determine product structures are the rate of crossover PIB⊕+ DVB (or DIB) → PIB‐DVB⊕(or PIB‐DIB⊕), the concentration of the linking agent DVB (or DIB), and the molecular weight of the PIB arm. Evidence for the formation of higher order stars (“secondar

ISSN:1022-1360    

DOI:10.1002/masy.19950950106

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe foundation and methodology of using highly reactive but non‐polymerizable monomers in living cationic polymerizations is introduced. The chemistry and kinetics of 1,1‐diphenylethylene (DPE) addition to living polyisobutylene (PIB) in methyl chloride/n‐hexanes 40/60 v/v at −80°C is reported. Monoaddition occurred even when large excess of 1,1‐diphenylethylene was used. The methanol quenched polymer of the DPE capped PIB carried ‐OCH3functionality exclusively, suggesting that the diphenyl alkyl chain‐ends are completely ionized, which was confirmed by conductivity studies. By in‐situ functionalization using soft nucleophiles a variety of functional groups were obtained, most notably ester upon reaction with silyl ketene acetal. It was found that the diphenyl carbenium ion is an efficient initiating species for the polymerization of reactive monomers such as vinyl ethers and α‐methylstyrene. The synthesis of PIB based block copolymers was accomplished by sequential monomer addition, using para‐methylstyrene, α‐methylstyrene or isobutyl vinyl ether as the second monomer. It involved capping with DPE, followed by tailoring the Lewis acidity to the reactivity of the second monomer by the addition of titanium(IV) alkoxide, by replacing the Lewis acid with a weaker one or by the use of a common ion salt. PIB‐b‐PMMA was obtained by the combination of living cationic and group tr

ISSN:1022-1360    

DOI:10.1002/masy.19950950107

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractKinetics of the living cationic polymerization of isobutylene, initiated by the systemt‐bu‐m‐DCC/TiCl4/2,4‐dimethylpyridine (2,4‐DMP), were studied as a function of concentration of the various components of the initiation system, solvent polarity, and presence of the protic acid scavenger, 2,6‐di‐tert‐butylpyridine (DTBP). Under a variety of conditions, the effective number of growing chains in a given polymerization remained constant and Mn increased linearly with monomer conversion. The system was found to yield an essentially homogeneous reaction mixture in hexanes/methyl chloride cosolvents, with only a small amount of precipitate, probably 2,4‐dimethylpyridinium salts resulting from proton scavenging by the tertiary amine. It was found that increasing [TiCl4] strongly increased the rate while increasing [2,4‐DMP]weakly decreased the rate. Evidence of a retardation of the polymerization rate by the soluble TiCl4:2,4‐DMP complex was observed. The addition of DTBP as a protic acid scavenger, with or without 2,4‐DMP, very weakly decreased the rate of polymerization. Increasing the fraction of methyl chloride in the solvent mixture caused an increase in the rate of polymerization. All of the results were consistent with a propagation mechanism in which an equilibrium exists between dormant and ion

ISSN:1022-1360    

DOI:10.1002/masy.19950950108

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractCertain metal‐catalyzed hydrosilations have been found to occur in a highly regioselective manner which makes them useful for the preparation of unique classes of ambifunctional monomers. These monomers bear two chemically different functional groups within the same molecule. By selection of the appropriate functional groups it is possible to design monomers in which the functional groups react independently, copolymerize, or polymerize by different mechanisms. This article describes some recent results of the synthesis and polymerization of several novel types of ambifunctional monomer

ISSN:1022-1360    

DOI:10.1002/masy.19950950109

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe living cationic polymerization of vinyl ethers was carried out with organoaluminum compounds in the presence of various types of esters and ethers (cyclic and acyclic), to find out the suitable added bases available for the living polymerization. The effects of the basicity and steric hindrance of added bases were investigated in detail. On the basis of these results, a fast living polymerization system was realized. To synthesize water‐soluble polymers such as thermally‐induced phase separating polymers and polyalcohols with well‐defined polymer structure, the living polymerization of various vinyl ethers was examined. The aqueous solution of living poly(vinyl ethers) having oxyethylene units exhibited a quite sensitive (ΔTps=0.3–0.5°C) and reversible phase separation on heating and cooling. The effects of polymer structures (pendant substituent, polymer sequence, molecular weight, and MWD) on the phase separation behavior were investigated. PVA and block copolymers containing PVA units with a narrow MWD were also prepared via living cationic polymerization of vinyl ethers and a deprotection

ISSN:1022-1360    

DOI:10.1002/masy.19950950110

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA new strategy for the synthesis of vinyl type macrocyclic polymers of controlled molecular weight and molecular weight distribution has been investigated. It involves the direct coupling of an α‐ω‐heterodifunctional linear polymer precursor previously prepared by living polymerization. The cyclization is achieved under high dilution, by an appropriate activation of one of the polymer‐ends in order to allow its reaction with the other end function. Its application to the preparation of polystyrenes and poly(vinyl ether)s with a macrocyclic structure, as well as ring closure mechanisms in the presence of different cyclization agents are r

ISSN:1022-1360    

DOI:10.1002/masy.19950950111

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper reports a living cationic ring‐opening polymerization of 2‐phenyl‐1,3,2‐dioxaphosphorinane (a six membered cyclic phosphonite, 1) initiated by a new catalyst system of a halobenzene with NiBr2. The polymerization proceeded in a living nature to produce a poly(phosphinate) 2. The polymerizations of seven‐and five‐membered cyclic phosphonites with this catalyst system are also described. The kinetic analysis of the polymerization of 1, initiated with this catalyst system, has successfully been carried out. The difference of the nature in the polymerizations of five‐, six‐, and seven‐membered monomers is discussed. Syntheses of linear and star‐shaped telechelic polymers using di‐, tri‐, tetra‐, and hexahalobenzenes as a catalys

ISSN:1022-1360    

DOI:10.1002/masy.19950950112

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY