Cationic polymerizations at elevated temperatures by novel initiating systems having weakly coordinating counteranions - 2. Isobutylene/isoprene copolymerizations
S. Jacob et al., Cationic polymerizations at elevated temperatures by novel initiating systems having weakly coordinating counteranions - 2. Isobutylene/isoprene copolymerizations, POLYM BULL, 41(5), 1998, pp. 503-510
As a sequel to our studies on isobutylene (IB) homopolymerizations, we have
investigated the copolymerization of IB/isoprene (IP) mixtures containing
up to similar to 20 mole% IP in the feed by the use of the in situ (CH3)(3)
Si[B(C6F5)(4)] initiating system in close-to-neat monomers in the temperatu
re range from -35 to -8 (reflux)degrees C. The effects of temperature and I
B/IP feed ratio on copolymer molecular weights were determined and compared
with those produced by AlCl3. The molecular weights of butyl rubbers obtai
ned by the novel initiating system under a variety of conditions are invari
ably and significantly higher than those made with AlCl3. High molecular we
ight gel-free rubbers containing up to similar to 5 mol% unsaturation can b
e obtained at relatively high temperatures. Copolymer compositions can be c
ontrolled by the IB/IP ratio in the feed. Product molecular weights decreas
e with increasing IP content. To gain insight into the copolymerization mec
hanism, the activation enthalpy of molecular weights (Delta H-double dagger
= -5.9 kcal/mol, -24.7 kJ/mol) and the reactivity ratios (r(IB) = 1.8, r(I
P) = 1.5) have been determined.