naphthaline etc especially preferred are aliphatic diols containing 2 to 8 carbon atoms equivalent ester forming derivatives of diols are also useful e g ethylene oxide or ethylene carbonate can be used in place of ethylene glycol the term 34 low molecular weight diols 34 as used herein should be construed to include such equivalent ester forming derivatives provided however that the molecular weight requirement pertains to diol only and not to its derivatives dicarboxylic acids which are reacted with the foregoing long chain glycols l in formula a and low molecular weight diols e in formula b to produce the copolyesters of this invention are aliphatic cycloaliphatic or aromatic dicarboxylic acids of a low molecular weight i e having a molecular weight of less than about 300 the term 34 dicarboxylic acids 34 as used herein includes equivalents of carboxylic acids having 2 functional carboxyl groups which perform substantially like dicarboxylic acids in reaction with glycols and diols in forming copolyester polymers these equivalents include esters and ester forming derivatives such as acid halides and anhydrides the molecular weight requirement pertains to the acid and not to its equivalent ester of ester forming derivative thus an ester of a dicarboxylic acid having a molecular weight greater than 300 or.