Compounds of formula (I):
wherein:
R represents H or a mono- or poly- carboxylic acyl group;
R¹ represents H or a carboxylic ester moiety;
R² represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group, or an aralkyl group, said groups being optionally substituted, or R² represents a carboxylic ester moiety;
n = 1 - 4;
Y is O or S;
and esters thereof,
are useful as heat and photo- stabilisers for polymeric materials.