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doi: 10.1002/masy.19981320103pmid: N/A
This presentation concerns subjective comments in respect to the status and foreseeable future of ionic polymerizations, i.e., cationic‐, anionic‐, and ionic ring opening polymerizations.
Bae, Young Cheol; Faust, Rudolf
doi: 10.1002/masy.19981320104pmid: N/A
The living cationic polymerization of isobutylene induced by the 2‐chloro‐2,4,4‐trimethylpentane/TiCl4/hexane:methyl chloride (60:40, v:v)/‐80°C system was studied in the presence of pyridine derivatives. Protic initiation, substantial in the absence of these additives, was virtually eliminated in their presence, and polyisobutylenes with controlled molecular weight and narrow molecular weight distribution were obtained. With some additives, however, proton elimination occurs, resulting in the exclusive formation of the exo olefin. The rate of elimination is independent of monomer concentration, i.e., it occurs during and after the polymerization. Results suggest that the proton elimination is due to the presence of an uncomplexed base, especially when complex formation with TiCl4 is hindered by steric compression, but its approach of the polymer cation is not fully blocked.
Charleux, Bernadette; Moreau, Michel; Vairon, Jean‐Pierre; Hadjikyriacou, Savvas; Faust, Rudolf
doi: 10.1002/masy.19981320105pmid: N/A
The use of non‐homopolymerizable monomers such as 1,1‐diphenylethylene (DPE) in the synthesis of functional polymers and block copolymers by cationic polymerization has been recently reported. The most important parameters in this process, the kinetics and extent of ionization and capping as well as the stability of the cation, were investigated by studying the reaction with TiCl4 of 1‐methoxy‐1,1‐diphenyl‐3,3,5,5‐tetramethylhexane, a model for DPE‐capped polyisobutene chain‐end. This study was performed using 1H NMR and the high‐purity stopped‐flow device coupled with UV‐visible spectroscopy.
Crivello, James V.; Rajaraman, Surésh K.
doi: 10.1002/masy.19981320106pmid: N/A
A wide variety of mono‐, di‐ and multifunctional allyl ethers and related compounds are readily polymerized using a newly discovered polymerization reaction which has been termed: a transition metal‐catalyzed tandem isomerization and cationic polymerization. Employing dicobalt octacarbonyl in combination with organosilanes, the polymerization of these monomers takes place rapidly to give high molecular weight polymers.
Deffieux, Alain; Schappacher, Michel
doi: 10.1002/masy.19981320107pmid: N/A
The grafting of polystyryl lithium onto poly(chloroethyl vinyl ether) chains has been investigated. The reaction proceeds cleanly and quantitatively thus allowing the synthesis of comblike polymers. Since the dimensions of the polystyrene branches and of the poly(chloroethyl vinyl ether) backbone can be controlled by living polymerizations, both the length and the number of branches of the graft copolymers can be tuned. The latter behave as star polymers. The possibility to initiate a new cationic polymerization of chloroethyl vinyl ether from polystyrene branches bearing acetal termini in order to prepare the corresponding stars with poly(chloroethyl vinyl ether‐b‐ styrene) branches is also examined. Finally access to hyperbranched polymers of controlled architecture and dimensions by deactivation of a second amount of polystyryl lithium onto the last blocks of poly(chloroethyl vinyl ether) is also reported.
Goethals, Eric J.; Reyntjens, Wouter; Lievens, Serge
doi: 10.1002/masy.19981320108pmid: N/A
The living cationic polymerization of vinyl ethers has been used to prepare a number of new polymers with special properties. Sequential polymerization of the hydrophilic methyl vinyl ether (MVE) and the hydrophobic octadecyl vinyl ether (ODVE) has lead to amphiphilic block‐copolymers with emulsifying properties for water/decane mixtures. Poly(vinyl‐ether) macromonomers were obtained by end‐capping of living polymers with hydroxyethyl acrylate. Copolymerization of polyODVE‐macromonomer with usual acrylates lead to highly branched hydrophobic polymers. When the end‐capping was performed with bifunctionally living polymers, the corresponding “bis‐macromonomers” were obtained. Copolymerization of such bis‐macromonomers with styrene or butyl acrylate, leads to the formation of segmented polymer networks. In the case of polyODVE‐poly(butyl acrylate), these networks showed a pronounced phase separation. Due to the crystallinity of the polyODVE domains, these materials showed shape memory properties.
doi: 10.1002/masy.19981320109pmid: N/A
This study is a comprehensive overview of the open problems and the existing views on the mechanism of quasiliving carbocationic polymerizations (QLCP) of olefins mediated by nucleophilic additives. The fundamental and general aspects of ideal living and quasiliving polymerizations involving other mechanisms, such as free radical, group transfer, ring‐opening metathesis, ring‐opening cationic and anionic processes, have been also analyzed and summarized. Quasiliving carbocationic polymerization of olefins in the presence of nucleophiles, which form complexes with the Lewis acid coinitiators, occur By reversible termination. Four different mechanisms have been discussed in this study: (1) reactivity leveling by nucleophiles (“electron donors”); (2) propagation by species with decreased ionicity (“stretched polarized bonds”) mediated by Lewis acid‐nucleophile complexes (LA‐Nu); (3) propagation by classical ion pair and free ion species; (4) proton scavenging by nucleophiles and 2,6‐di‐teri‐butylpyridine proton trap. It is shown that mechanisms No. 1, 3 and 4 cannot explain all the existing findings, and although the experimental results can be interpreted with mechanism No. 2, the existence of “stretched polarized bonds” can be questionable. It is also concluded that compared to nonliving carbocationic polymerization, kinetic analysis indicates that the propagating species cannot be the same in quasiliving carbocationic polymerizations and in chain transfer dominated classical carbocationic polymerizations with ion pairs and free ions.
Kanaoka, Shokyoku; Higashimura, Toshinobu; Sawamoto, Mitsuo
doi: 10.1002/masy.19981320110pmid: N/A
This paper discusses the nature of the living growing species in cationic polymerization from the viewpoint of the steric structure of poly(isobutyl vinyl ether) (poly(IBVE)). At −78 °C, living polymerization was induced with the HCl‐IBVE adduct (1)/ZnCl2 system in a EtNO2/CH2Cl2 mixture, whereas similar systems with EtAlCl2 led to conventional cationic polymerization. In this polar medium, both systems gave polymers with very similar and low isotacticity (meso ≈ 56%), indicating that the propagating reaction is mediated by free ions. Thus, regardless of solvent polarity, or involvement of free ions or ion pairs, living cationic polymerization requires a suitably nucleophilic counteranion. As model reactions of the growing species, 1/ZnCl2 and 1/EtAlCl2 were directly analyzed by 1H NMR spectroscopy.
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