Formation and reactivities of free ions in cationic polymerisation

Stable salts of carbocations such as triphenyl methyl and especially tropylium ion are useful initiators for cationic polymerisation of reactive olefins such as alkyl vinyl ethers and vinyl carbazoles. Although it is now clear that reaction kinetics are more complex than was originally assumed, use of tropylium hexachloroantimonate as initiator gives a useful estimate of the order of magnitude for free ion propagation rate coefficients in the systems studied. Polymerisation of carefully purified N-ethyl-3vinylcarbazo!e by c 7 H2SbC16 in CH 2 c1 2 at 0C yields an estimate for k+ = 2 x 10+ M-l sec 1 which is Some twenty times smaller than that f8r the closely related monomer N-vinylcarbazole. Distinguishing aspects of the cationic polymerisation of N-ethyl-3-vinylcarbazole are the ve~ high molecular weights obtained and the linear dependence of Ml on the monamer/catalyst mole ratio, indicating that transfer aHd termination are comparatively unimportant.