New epoxide initiators for the controlled synthesis of functionalized polyisobutylenes

The mechanism of initiation was investigated in isobutylene OB) polymerizations initiated by epoxidized alpha -methylstyrene (MSE) and 1,2-epoxy-2,4,4-trimethylpentane (TMPO) in conjunction with TiCl4. The proposed mechanism predicts primary OH head groups and tertiary Cl end groups in the PIE. Model studies conducted with MSE/TiCl4 and diisobutylene lead to ring closure yielding a substituted furanyl structure. Real-time fiber-optic refractive index monitoring was used to follow the initiation with the TMPO/TiCl4 system. It was found that the cleavage of TMPO proceeds simultaneously by S(N)1 and S(N)2 mechanisms as proposed. The carbocation forming by the S(N)1 route is proposed to initiate the polymerization of IB, but it was shown that excess TiCl4 relative to TMPO was necessary for propagation. Isomerization and polyether formation by the S(N)2 pathway lead to side reactions, reducing the initiating efficiency.