Polymerization of methyl methacrylate by organometallic compounds—IV: Mechanism of polymerization and copolymerization initiated photochemically by triethyl-aluminium — monomer complexes

Abstract

The photoinitiated polymerization of methyl methacrylate by triethyl-aluminium is shown to occur by a free radical mechanism, initiated by a photoexcited state of a 1:1 Wittig ‘-ate’ complex between MMA and Et 3Al. A survey of related compounds shows that only monomers having an unsaturated group, containing an atom possessing filled, non-bonding orbitals, conjugate with the vinyl group, polymerize in the presence of Et 3Al at ambient and below ambient temperatures. The formation of a complex between monomer and Et 3Al is a prerequisite for polymerization. However, these complexes, e.g. MMA:AlEt 3, can initiate polymerization of monomer inert to Et 3Al, e.g. styrene. No anionic polymerization occurs in the MMA:Et 3Al system. However a 1:2 MMA:Et 3Al complex, which prevails when Et 3Al is in excess, undergoes rapid reaction in the dark to form nucleophilic addition products involving the carbonyl group of the monomer.