"wherein A1 is a terminal group derived from the present polycarboxylic acid; when the present polycarboxylic acid is tricarboxylic acid, it is (HO2 C)2 (R)CO2 -- and when it is tetracarboxylic acid, it is (HO2 C)3 (R)CO2 -- wherein R is a polycarboxylic acid residue, A2 is a diester group derived from the present polycarboxylic acid, B is a residue derived from the present polyol, and l, m and n a" . . . .