Cationic beta-Scission of C H and C C Bonds for Selective Dimerization and Subsequent Sulfur-Free RAFT Polymerization of alpha-Methylstyrene and Isobutylene

A series of exo-olefin compounds ((CH3)(2)C(PhY) CH2C(=CH2)PhY) were prepared by selective cationic dimerization of a-methylstyrene (alpha MS) derivatives (CH2=C(CH3)PhY) with p-toluenesulfonic acid (TsOH) via beta-C H scission. They were subsequently used as reversible chain transfer agents for sulfur-free cationic RAFT polymerization of aMS via beta-C C scission in the presence of Lewis acid catalysts such as SnCl4. In particular, exo-olefin compounds with electron-donating substituents, such as a 4-MeO group (Y) on the aromatic ring, worked as efficient cationic RAFT agents for aMS to produce poly(alpha MS) with controlled molecular weights and exo-olefin terminals. Other exoolefin compounds (R CH2C(=CH2)(4-MeOPh)) with various R groups were prepared by different methods to examine the effects of R groups on the cationic RAFT polymerization. A sulfur-free cationic RAFT polymerization also proceeded for isobutylene (IB) with the exoolefin aMS dimer ((CH3)(2)C(Ph) CH2C(=CH2)Ph). Furthermore, telechelic poly(IB) with exo-olefins at both terminals was obtained with a bifunctional RAFT agent containing two exo-olefins. Finally, block copolymers of aMS and methyl methacrylate (MMA) were prepared via mechanistic transformation from cationic to radical RAFT polymerization using exo-olefin terminals containing 4-MeOPh groups as common sulfur-free RAFT groups for both cationic and radical polymerizations.

Automated summary

A series of exo-olefin compounds were prepared by selective cationic dimerization of α-methylstyrene derivatives with p-toluenesulfonic acid, and they were used as reversible chain transfer agents for sulfur-free cationic RAFT polymerization. The effects of different R groups on the cationic RAFT polymerization were examined, and block copolymers of α-methylstyrene and methyl methacrylate were synthesized via mechanistic transformation from cationic to radical RAFT polymerization.