| abstract |
A process for polymerising a cyclic monomer comprises the step of forming a mixture of the monomer with a catalyst compound wherein the catalyst compound comprises a reaction product of a reactive titanium, zirconium, hafnium or aluminium compound with a hydroxycarboxylic acid or derivative thereof, with a proviso that when the cyclic monomer has more than five carbon atoms in the ring the catalyst does not comprise a Group IVB metal lactate of general formula M(OCH(CR3)CO2H)2(OH)2, where M is a Group IVB metal, or its aqueous solution or alkali-neutralised salt. The catalyst may comprise a compound having the general formula aM(L)b(OR)(av)-(bw), where OR is an alkoxide, L is a fully or partially deprotonated, optionally derivatised, hydroxycarboxylic acid ligand, M represents a metal selected from titanium, zirconium, hafnium or aluminium, a is the number of metal atoms, v is a number equal to the valency of the metal M, b is a number from 1 to a times v and w is the number of deprotonated groups on each hydroxycarboxylic acid ligand. Also disclosed is a polymerisable mixture comprising at least one cyclic carbonate, cyclic carbamate, lactide, cyclic lactone or other cyclic compound containing two heteroatoms and 5 or fewer carbon atoms, and a catalyst formed from the reaction of a titanium, zirconium, hafnium or aluminium compound with a hydroxycarboxylic acid or derivative thereof, such as lactic acid or an ester of lactic acid. |