摘要:

AbstractThis presentation concerns our latest results for the controlled synthesis of various homopolymers, blocks, random copolymers, networks, by living carbocationic polymerization (LC⊕Pzn). We start with an analysis of the Winstein ionicity spectrum, a roadsign toward LC⊕Pzn systems. Living isobutylene (IB) homopolymerization can be effected by the addition of common anion salts to conventional polymerization charges, e.g., by adding nBu4NCl to a 2‐chloro‐2,4,4‐trimethylpentane (TMPCl)/TiCl4/IB system. Various AB diblocks have been prepared by sequential monomer addition. The first clean svnthesis of an AB poly(olefin‐b‐alkyl vinyl ether) diblock, ie., poly(isobutylene‐b‐methyl vinyl ether), by sequential monomer addition was accomplished. These novel amphiphilic diblocks promise to be excellent nonionic detergents. The field of linear A‐B‐A triblocks and three‐arm star blocks where A = glassy and B = rubbery (polyisobutylene) segment, is vigorously expanding. Several new thermoplastic elastomers (TPEs) have been prepared, characterized and tested, e.g., poly‐(indene‐b‐isobutylene‐b‐indene). The synthesis of random copolymers, e.g., isobutylene/2,4,4‐dimethyl‐1,3‐pentadiene, by living reactivity leveling has been demonstrated. Transformation of the polyisobutylene cations PIB⊕and⊕PIB⊕yielded the corresponding anions PIB⊖and⊖PIB⊖, which upon block polymerization of butadiene (Bd) and methyl methacrylate (MMA), respectively, gave rise to the new diblock PIB‐PBd and triblock PMMA‐PIB‐PMMA. In the latter, the largely syndiotactic sPMMA endblocks were stereocomplexed with isotactic iPMMA and thus the upper use‐temperature of these novel TPEs was enhanced. Novel amphiphilic networks comprising hydrophilic polymethacrylates (e.g., dimethylaminoethyl methacrylate (DMAEMA) or hydroxyethyl methacrylate (HEMA)) crosslinked by methacrylate‐telechelic PIBs were prepared and their pote

ISSN:0258-0322    

DOI:10.1002/masy.19920600103

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe cationoid living polymerisations have many of the characteristics of pseudo‐cationic (φ‐cat) polymerisations and none of those of cationic polymerisations. In contrast to the φ‐cat polymerisations by protonic acids, which are transfer‐dominated, those giving living polymerisations are propagated by esters which are part of a donor‐acceptor complex involving a “third reagent”. There are three types: The first is exemplified by an ester which is activated by a metal halide, e.g. HMI (from monomer M + HI) + ZnBr2, or oligoisobutyl acetate + BCl3. The second type is exemplified by a polymer triflate complexed by a dialkyl sulphide. The reagents which change the reactivity of the ester are termed “modifiers”. The acceptors, e.g. ZnBr2, which co‐ordinate to a donor group on the polymer, are positive modifiers (or activators). The donors, such as R2S, which coordinate onto an acceptor group at the end of the polymer, e.g. the acidic β‐H, are negative modifiers (or moderators).The propagation by both types of modified ester probably involves a 6‐centred cyclic transition state. The same applies to a third type of φ‐cat propagation, in which a polymeric ester reacts with a D‐A complex formed from M + I2.The formation of unwanted non‐living polymers of high DP and/or broad DPD, together with those resulting from living polymerisations, happens because the metal halides used in these reactions not only form the φ‐cat propagating centres, but also react with ionogenic impurities to initiate concurrent, short‐lived cationic polymerisations. These parasitic reactions can be suppressed by an excess of base, e.g. an ester or halide ions, which scavenge protons and carbenium ions. This phenomenon indicates that, whatever else is propagating the living polymerisations, it is unlikely to be carbenium ions.The kinetic equations for the living polymerisations, developed here, make it possible to calculate propagation rate‐constants from rate and DP data; such calculations are

ISSN:0258-0322    

DOI:10.1002/masy.19920600104

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe polymerizations of isobutylene initiated with the system tert‐butyl chloride (t‐BuCl)/SnCl4and carried out in CH2Cl2at −20°C and −78°C were investigated. The results obtained demonstrate that the presence of t‐BuCl in the polymerizing system gives rise to a PIB product with a distinctly bimodal MWD. The higher‐molecular weight (HMW) PIB,M̄n= 20000, I=M̄w/M̄n∼ 2.5, is the result of existence of the protogenic initiation with residual water in the reaction system. The lower‐molecular weight (LMW) PIB,M̄n<600,M̄w/M̄n≤ 1.4, is the product of polymerization initiated presumably with a complex t‐BuCl‐SnCl4‐H2O. To elucidate the reaction mechanism of the polymerization initiated with the complex, a series of similar isobutylene polymerizations using the initiation system 2,5‐dichloro‐2,5‐dimethylhexane (DDH)/SnCl4was run and the oily LMW PIB samples were investigated by1H‐NMR. A new polymerization mechanism describing

ISSN:0258-0322    

DOI:10.1002/masy.19920600105

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper overviews three living cationic polymerization systems (for styrene,p‐methoxystyrene, and isobutyl vinyl ether) that are, in common, featured by:(i) specifically in nonpolar solvents, the use of the hydrogen halide/metal halide initiating systems (HX/MXn; X: I, Br, Cl; MXn: ZnX2, SnCl4), which generate a living growing carbocation stabilized by a nucleophilic counteranion (X−…MXn);(ii) specifically in polar solvents, the use of externally added ammonium salts (nBu4N+Y−; Y−: I−, Br−, Cl−), which permit the generation of living species from HX/MXnby providing nucleophilic halogen anions Y−, either the same as or different from th

ISSN:0258-0322    

DOI:10.1002/masy.19920600106

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractIn spite of the difunctionality of the monomers, cationic polymerization of 1,3‐ and 1,4‐diisopropenylbenzene does not lead to branched or cross‐linked products. Instead, soluble polymers are obtained, containing the 1,1,3‐trimethylindane system as repetitive unit along the backbone. These polymers are interesting materials because of their high glass transition temperature (200°C‐250°C) and good thermal stability in air (2% weight loss at 450°C). Although the molar mass of the polyindanes seems to be limited due to a side reaction, it is possible to produce telechelic polyindanes. Substitution of an alkyl side chain onto the isopropenyl groups of 1,4‐diisopropenylbenzene leads to monomers which yield substituted polyindanes with glass transition temperatures as low as 26°C. Such polymers still exhibit good thermal stability: at 340°C a weight loss of only 2% occurs. 1,4‐Diisopropenylbenzene can even be anionically polymerized to linear polymers. In this case, the resulting polymer possesses isopropenyl phenyl side groups, which can be used as initiators for cationic polymerization of isobutene to obtain

ISSN:0258-0322    

DOI:10.1002/masy.19920600107

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractIt has previously been proposed (Ref. 1) that in the cationic vinyl polymerizations, proceeding with termination due to the collapse of ion pairs, addition of bases increases “livingness”, because of the fast convertion of the otherwise dead (within the time of polymerization) covalent species into the onium ions; these, in turn, fast convert into carbenium ions, the actually propagating species.Equilibria between carbenium ions (CH3OCH2+A−has been used as a model) and their onium counterparts ((CH3)2O taken as a model base) as well as between covalent species (CH3OCH2OSO2CF3) and the corresponding oxonium ion (with a (CH3)2O ligand) have been studied by dynamic1H and19F NMR. Total ionization of methoxymethyl triflate (CH3OCH2OSO2CF3) has been shown to increase indeed from 104(‐10°C) to 106(‐70°C) times when 1,0 mol·L−1of (CH3)2O is added.Although this model system better describes polymerization of cyclic acetals than that of vinyl ethers,it shows at least qualitativelythe importance of bases in ionization of covalent species, which may be responsible for reinitiation in the cationic polymerization o

ISSN:0258-0322    

DOI:10.1002/masy.19920600108

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractPolymerization of styrene initiated by triflic acid in CH2Cl2solution was reexamined, using a new stopped‐flow device working in high purity conditions over a wide temperature range. Monomer and styryl cation were followed simultaneously through their respective absorbances at 290 and 340 nm. Initiation is very rapid, and cations concentration reaches a plateau the duration of which is depending on temperature. In our conditions (I0= 0.5 − 9.10−3M, M0/I0= 1 to 20), cations concentration is so low at room temperature that it is almost unmeasurable. At −65°C, it is 100 times higher, remains constant for several seconds and complete termination takes place within a minute or more. Such a profile of cation evolution agrees with an equilibrium situation between initiation and a much more temperature‐dependent backward deprotonation. Apparent initial rate of initiation is first order with respect to monomer, but the order with respect to initiator was found very high and variable with temperature (from 4.5 at −65°C to 3 at −20°C). This supports the presence, even if they are in low concentration, of acid high agregates, the reactivity of which increases with size. A first order monomer consumption is observed during the plateau, which leads to kpvalues ranging from 103at −65°C to 9.104M−1.s−1at −10°C (Ep#= 43 kJ.mol−1). The disappearance of cations, which follows the plateau, slows down and becomes unimolecular when monomer consumption is complete, and ktvalues range from 6.10−2s−1at −65°C t

ISSN:0258-0322    

DOI:10.1002/masy.19920600109

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe importance of exchange reactions between various types of active species present in the cationic polymerization of alkenes is addressed. Reactivities of carbocations, corresponding ion pairs, onium ions, and covalent species are discussed for model systems and in real polymerization. The influence of various parameters on the equilibria between carbenium ions, onium ions, and covalent species is described. Rate constants of the isomerization of active sites are estimated and correlated with polydispersities. General ways to improve control of cationic polymerization of alkenes are discussed.

ISSN:0258-0322    

DOI:10.1002/masy.19920600110

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractTrimethylenecarbonate (TMC) and neopentane diol carbonate (NPC) were polymerized with two groups of initiators, proton and carbenium ion donors or Lewis acids. Initiation with methyltriflate, triflic acid or triethyloxonium tetrafluoroborate in solution gave satisfactory yields (up to 90%) but only low molecular weights (Mn105) were obtained. However, in analogy to triflic acid initiated polymerizations all polycarbonates contain ether groups. The molar fraction of the ether groups increases with the reaction temperature. High molecular‐weight polycarbonates containing ether groups were also obtained with other strong Lewis acids such as SnCl4, SnBr4and TiCl4. In contrast, weak Lewis acids such as Bu2SnBr2Bu3SnOMe and Sn(II)2‐ethylhexanoate yield polycarbonates free of ether groups. This finding and the NMR‐spectroscopically identified endgroups suggest that these weak Lewis acids initiate an insert

ISSN:0258-0322    

DOI:10.1002/masy.19920600111

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractGeneral aspects of the photoinitiated free radical promoted cationic polymerization are discussed. The applicability of pyridinium salts, a new class of photoinitiators, of appropriate redox potentialEred1/2in oxidizing carbon‐centered free radicals to carbocations capable of initiating the polymerization of various compounds is demonstrated. Moreover, the use of polysilanes as source for readily oxidizable free radicals is described. Furthermore, possibilities for preparing block copolymers by free radical promoted cationic polymerization are pointed ou

ISSN:0258-0322    

DOI:10.1002/masy.19920600112

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY