Gabor Kaszas

Living carbocationic polymerization of resonance-stabilized monomers

Abstract Living polymerization has been at the forefront of polymer science and engineering in recent years. The term “living” is used to distinquish polymerizations in which chain breaking processes such as termination and transfer reactions are absent. Living polymerization provides for the control over the molecular weight (MW) and molecular weight distribution (MWD) of the polymer sample. This paper will give a general overview about living carbocationic polymerization, followed by a review of recent developments with emphasis on resonance-stabilized monomers and the use of the living concept for the design and synthesis of new polymeric structures.

Electron pair donors in carbocationic polymerization: I. Introduction into the synthesis of narrow molecular weight distribution polyisobutylenes

SummaryLow molecular weight (¯Mn ∼900–5000) narrow molecular weight distribution (MWD; ¯Mw/Mn = 1.1–1.2)tert.-chlorine telechelic polyisobutylenes (PIBs) have been synthesized by the use of thetrans-2,5-dimethyl-2,5-diacetoxy-3-hexene (DiOAcDMeH6)/BCl3 initiating system in the presence of the electron donor (ED) dimethyl sulfoxide (DMSO) in methyl chloride diluent at −30°C. The living character of the polymerization was demonstrated by linear Mn versus Wp (weight of polymer) plots starting at the origin with the slope of 1/[Io] (where [Io] = initiator concentration). DMSO reduces the overall rate of polymerization, however, it increases the initiator efficiency (Ieff) to ∼100%. The number averagetert.-chlorine end functionality is -Fn=1.97±0.04, by1H NMR spectroscopy. Polymerization mechanistic details are discussed. This is the first time narrow MWDtert.-chlorine telechelic PIB has been prepared close to the reflux temperature of methyl chloride.

Electron-pair donors in carbocationic polymerization. III: Carbocation stabilization by external electron-pair donors in isobutylene polymerization

Abstract The polymerization of isobutylene (IB) initiated by a variety of tertiary chloride/TiCl4 or BC13 systems can be very beneficially influenced by deliberately added electron-pair donors (EDs). EDs whose Gutmanns 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)/TiCl4 or 2-chloro-2,4,4-trirnethylpentane (TMPCl)/TiCl4 give rise to very narrow molecular weight distribution (MWD) polyisobutylene (PIB) ( M w / M n = 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/BCl3 system becomes active and induces living IB polymerization to narrow-MWD product; (4) indanyl end-group formation, which may occur in the CumCl/BCl3 or p-dicumyl chloride/BCl3, inifer systems, is eliminated. The effect of reaction conditions,...

Polyisobutylene-based thermoplastic elastomers : A review

Abstract This paper honours the 40th anniversary of the discovery of the living polymerization concept. Polymeric materials exhibiting both thermoplastic and elastomeric characteristics have a variety of unique properties which makes them valuable articles of commerce. Such thermoplastic elastomers or TPEs, schematically represented in Scheme 1, are block copolymers — ABA linear triblock, A(BA)n linear alternating block or (AB)n−X radial block, where A is a thermoplastic glassy block with a high glass transition temperature (Tg) while B is an elastomeric block with a low Tg. These TPEs behave like vulcanized rubbers at room temperature and like thermoplastics at elevated temperatures. Thus the materials can be melt extruded like plastics, while retaining their beneficial rubbery properties upon cooling. This ability is not only of advantage during processing, but allows the materials to be reprocessed, which is of importance from both the material savings and the environmental protection point of view. Th...

Quasiliving Carbocationic Poiymerization. III. Quasiliving Polymerization of lsobutylene

Abstract The polymerization of isobutylene has been investigated by the use of the steady, slow, continuous monomer addition technique in the presence of a variety of initiating systems, i.e., “H2O”/TiCl4, “H2O”/AlCl3, C6H5C(CH3)2Cl/TiCl4, p-ClCH2 C6(CH3)4* CH2Cl/AlCl3 at -50°C. Quasiliving polymerizations have been obtained with the “H2O” and C6H5(CH3)2Cl/TiC14 systems in 60/40 v/v n-hexane/methylene chloride solvent mixtures with very slow monomer input. After a brief “flash” polymerization, the M n of PIB increased linearly with the cumulative amount of monomer added (consumed); however, the number of polymer molecules formed also increased, indicating the presence of chain transfer to monomer. With the “H2O”/TiCl4 initiating system, M n,max was 56,000 and M w /M n < 2.0. By the use of the C6H5C(CH3)2CL/TiCl4 initiating system, quasiliving polymerization has been achieved and chain transfer could virtually be eliminated.

Quasiliving Carbocationic Polymerization. XII. Forced Ideal Copolymerization of lsobutylene with Styrene

Abstract Forced ideal carbocationic copolymerization of isobutylene/styrene systems has been achieved by continuous addition of mixed monomer feeds to 2-chloro-2,4,4-trimethylpentane/TiCl4 in n-hexane/methylene chloride charge by keeping the input rate equal to the overall rate of copolymerization. The composition of the copolymers was identical to that of the feeds over the entire monomer concentration range. The number-average molecular weight of the copolymers increased almost linearly with the amount of consumed monomers at higher isobutylene concentrations in the feed. The molecular weight increase was less pronounced at higher styrene concentration because more methylene chloride had to be used in the solvent system to keep the copolymer in solution. The micro-structure of the copolymers is uniform as determined by gel permeation chromatography (UV plus RI) and 13C-NMR spectroscopy According to these studies, true copolymers have formed. The probability of triads in the copolymer has been determined.

New Transparent Flexible UV-Cured Films from Polyisobutylene-Polyisoprene Block Polymers

Abstract Novel polyisobutylene-polyisoprene (PIB-PIP) multiblock polymers have been synthesized and used for the preparation of UV-cured transparent flexible coatings. The block polymers were tailor-made by bidirectional living carbocationic polymerization of isobutylene (IB) followed by sequential isoprene (IP) addition. PIB-PIP multiblocks containing highly cyclized tr-1,4-PIP sequences were mixed with a bisazide and photocrosslinked. Epoxidized PIB-PIP blocks were blended with a cationic photoinitiator and UV-cured. Blocks having 23 mol% total PIP content and PIB segments of M n = 16,600 and 18,800, respectively, gave transparent flexible coatings with 45 kg/cm2 tensile strength and 450% elongation. The coatings exhibited good adhesion to aluminum and are expected to have excellent barrier properties due to the presence of PIB sequences.

Living carbocationic polymerization. XXXIII: Living polymerization of isobutylene by tertiary hydroxyl/boron trichloride/electron pair donor systems

AbstractTert-alcohols in conjunction with BCl3 plus strong electron pair donors (EDs), such as dimethyl sulfoxide (DMSO) and dimethyl acetamide (DMA), have been found efficiently to initiate the living polymerization of isobutylene (IB) in methyl chloride diluent yielding narrow molecular weight distribution (MWD) polyisobutylenes (PIBs). For example, the aliphatic diol 2, 6-dihydroxy-2,4,4,6-tetramethylheptane/BCl3/ IB/DMA/−45°C system yields lineartert-chlorine telechelic

Micromechanical Testing of Polyisobutylene—Polystyrene Block-Type Thermoplastic Elastomers

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