Studies on polymers from cyclic dienes. XIII. Cationic polymerization of spiro[4,4]nona-1,3-diene

Polymerization and copolymerization of spiro[4,4]nona-1,3-diene were conducted with several cationic initiators. The homopolymer was formed slowly only in polar CH₂Cl₂ and/or at 0°C. The polymer was white, amorphous powders of relatively low molecular weight (1500—1700). No polymer was obtained with anionic initiators. Spectroscopic data indicated that the monomer unit contained trisubstituted double bonds instead of disubstituted counterparts. This result was explained by assuming isomerization to occur during propagation. Apparently, the severe steric crowding suppressed the usual 1,2- and 1,4-additions. The following reactivity ratios were obtained for spirononadiene (M₁) and α-methylstyrene (M₂) (BF₃OEt₂, toluene, −78°C): r₁=0.0, r₂=25±15. This result was again indicative of the steric hindrance of the spiro cyclopentyl group lowering the reactivity of the cyclopentadiene ring when compared with cyclopentadiene.