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

Abstract

A series of exo‐olefin compounds ((CH3)2C(PhY)–CH2C(=CH2)PhY) were prepared by selective cationic dimerization of α‐methylstyrene (αMS) derivatives (CH2=C(CH3)PhY) with p‐toluenesulfonic acid (TsOH) via β‐C–H scision. 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 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 αMS to produce poly(αMS) with controlled molecular weights and exo‐olefin terminals. Other exo‐olefin 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 exo‐olefin αMS dimer ((CH3)2C(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 αMS and 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.