Polymer, process and composition

A process for preparing a copolymer having a low molecular weight and high glass transition temperature, wherein the process comprises conducting a solution polymerisation process of a monomer composition comprising:

• (a) from 20 to 80 wt-% of at least one itaconate functional monomer not containing acidic groups or precursor acid groups,
• (b) not more than 40 wt-% of an acid functional monomer in an amount sufficient to achieve an acid value from 160 to 325 mg KOH per g of solid copolymer, and
• (c) optionally not more than 72 wt. % of monomers other than monomers (a) or (b);
• wherein
• the weight percentages of monomers (a), (b) and (c) total 100% and are calculated as a proportion of the total amount of monomers in the copolymer being 100%;
• and with the provisos:
• (I) the copolymer has a number average molecular weight (Mn) of no more than 15 kilograms per mole;
• and
• (II) the copolymer has a glass transition temperature of at least 75° C., and
• (III) the copolymer contains less than 40 wt-% vinyl aromatic monomer;
• and optionally
• (IV) the copolymer contains less than 40 wt-% methacrylate monomer.