The Effect of Counteranions in the Polymerization of Isobutyl Vinyl Ether Initiated by Triphenylmethyl Cation

Abstract

ABSTRACT:The cationic polymerization of isobutyl vinyl ether was carried out at -75°C by using triphenylmethyl salts (Ph3C+X-, X-=BF4-, AlCl4-, AlBr4-, SbCk and SnCh-J as initiator. The polymer was shown to contain the triphenylmethyl group. The extent of chain transfer, determined from the content of the triphenylmethyl group, was 0-4.4 in all the systems studied. These values are much smaller than those reported with BF3OEt2. The steric structure of the polymer was inferred from the precipitation temperature of the polymer in methyl ethyl ketone, Tp, as suggested by Okamura, et al. Tp decreased with increasing polarity of polymerization solvents. In less polar media, Tp decreased in the following orderThe observed order of Tp agreed with that of anion sizes, except for SnCh-. Thus it is suggested that the steric effect of the counteranion is an important factor in deciding the steric course of propagation for tight ion-pairs. These results were explained within the framework of the steric course of the cationic propagation which we had proposed previously.

Stable organic cation salts: Ion pair equilibria and use in cationic polymerisation

“…The earlier work involved poorly defined counterions, but subsequent results using a variety of PhaC + salt initiators with well defined counterions (28,29) confirmed the original suggestions. Primary factors in propagation seem to be the conformation of the polymer the spatial arrangement of the counterion and approaching monomer, and the direction of monomer attack, which is determined by the tightness of the ion pair and/or the size of the counterion.…”

“…In the least polar solvents, when presumably largely tight ion pairs are present, Aso found for both ~-methylstyrene (29) and isobutyl vinyl ether (28), that the degree of isotacticity was a maximum, with monomer attack being via the "back" side. As the solvent polarity increased and presumably the ion pair tightness decreased, possibly with some dissociation to free ions, "back" side attack becomes less favourable and isotacticity falls.…”

“…They allow the negative counterion to be well defined (28,29), whereas with other initiators, e.g. H20/BF3, it is only possible to speculate concerning the structure of the counterion.…”

“…Those olefins having double bonds sufficiently electron rich to react significantly with these salts include the common monomers, alkyl vinyl ethers (28,(79)(80)(81), N-vinylcarbazole (82)(83)(84) p-methoxystyrene (21,67), indene (34,74,85), cyclopentadiene (85,86), and vinylnaphthalenes (87). Styrene itself (60, 76, 77, 88-9t), a-divinylbenzene (92), ~-methylstyrene (88), linear conjugated dienes (93) and ~-olefins are much less reactive (i.e.…”

Some effects of the initiator on the cationic polymerization of alkenes

“…Photo-induced cationic polymerization of a-methylstyrene. 37 Temperature dependence of the rate of polymerization, R p (arbitrary units). 34 A re-examination of these results shows that the second-order rate constant has a shallow minimum near À65 8C, but this has not been examined further.…”