Graft Copolymers by Combined Anionic and Cationic Polymerizations Based on the Homopolymerization of a Bifunctional Monomer *

The bifunctional monomer 2-(vinyloxy)ethyl methacrylate (VEMA) was polymerized both anionically and cationically. Using 1,1-diphenylhexyllithium (DPHL) as initiator, tetrahydrofuran (THF) as solvent and the low temperature of −60°C, the C═C double bond of the methacryloyl group of VEMA underwent smoothly anionic polymerization, without cross-linking or side reactions. The polymer had a controlled molecular weight and a narrow molecular weight distribution (M _w /M_n = 1.06–1.12). On the other hand, the C═C double bond of the vinyloxy group of VEMA can undergo cationic polymerization. A polymer with controlled molecular weight and narrow molecular weight distribution (M _w /M _n = 1.11–1.13) was prepared using 2-[1-acetoxyethoxy]ethyl methacrylate (4)/EtAlCl₂ as initiator in the presence of THF, a weak Lewis base. Two methods were employed to prepare graft copolymers. 109(A) The anionically prepared polymer of VEMA was separated from solution after quenching the polymerization and purified by freeze-drying; then the vinyloxy groups of the side chains were allowed to react with trifluoroacetic acid to generate a macroinitiator, which finally induced the cationic graft polymerization of isobutyl vinyl ether (IBVE). This procedure yielded a graft copolymer with a polymethacrylate backbone and poly(IBVE) side chains containing a small amount of the IBVE homopolymer. (B) The anionic polymerization of 4 was carried out in THF without quenching, to produce a solution of macroinitiator. Then, in contrast to the first method, the polymer was not separated and toluene and IBVE were introduced into the system. Further, the cationic graft polymerization of IBVE was induced by adding an activator (EtAlCl₂). The THF, which was used as solvent in the anionic polymerization of 4, acted as a Lewis base in the cationic polymerization step. This procedure yielded a pure graft copolymer with controlled molecular weight and narrow molecular weight distribution (M _w/M _n = 1.15–1.17), consisting of a polymethacrylate backbone and poly(IBVE) side chains.