Abstract: An amphipathic co-polymer having a weight average molecular weight of from 2,500 to 20,000 inclusive and comprising an addition polymer backbone and at least one C.sub.1-4 alkoxy polyethylene or polyethylene copropylene glycol acrylate or methacrylate stabilizer unit where the backbone comprises up to 30% by weight of non-functional structural units and at least 70% by weight in total of stabilizer units and functional units where the functional units are optionally substituted styrene-containing units, hydroxy group-containing units and carboxyl group containing units, such that the proportions of hydroxy groups to carboxyl groups to styrene groups to propylene-oxy or ethylene-oxy groups are respectively 1 : 0.10-26.1; 0.28-25.0; 0.80-66.1.