Cationic β-Scission of C-H and C-C Bonds for Selective Dimerization and Subsequent Sulfur-Free RAFT Polymerization of α-Methylstyrene and Isobutylene.

A series of exo-olefin compounds ((CH ) C(PhY)-CH C(=CH )PhY) were prepared by selective cationic dimerization of α-methylstyrene (αMS) derivatives (CH =C(CH )PhY) with p-toluenesulfonic acid (TsOH) via β-C-H scission. They were subsequently used as reversible chain transfer agents for sulfur-free cationic RAFT polymerization of αMS via β-C-C scission in the presence of Lewis acid catalysts such as SnCl . 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 αMS to produce poly(αMS) with controlled molecular weights and exo-olefin terminals. Other exo-olefin compounds (R-CH C(=CH )(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 exo-olefin αMS dimer ((CH ) C(Ph)-CH C(=CH )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 αMS 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.