polyol should be sufficient to cure to a solvent resistant coating generally the hydroxyl number of the polymeric polyol will be at least about 40 and preferably will be in the range of about 100 to 300 based on resin solids examples of hydroxyl polymers useful as suitable crosslinking agents are those which are formed from reacting a polycarboxylic acid or its functional equivalent thereof with one or more polyols examples of suitable polycarboxylic acids include dicarboxylic acids such as saturated aliphatic dicarboxylic acids for examples adipic acid and azelaic acid aromatic acids such as isophthalic acid and terephthalic acid ethylenically unsaturated dicarboxylic acids such as fumaric acid and itaconic acid or functional equivalents of the acids such as anhydrides where they exist and lower alkyl esters of the acids can be used examples include succinic anhydride phthalic anhydride and maleic anhydride the molecular weight of both the ester polymers and the hydroxyl polymers adapted to be transesterified in accordance with this invention preferably are lower molecular weight polymers having number average molecular weight broadly between 200 and 50 000 and preferably between 500 and 20 000 as measured by gel permeation chromatography gpc in accordance with astm d 3016 78 astm d 3536 76 astm d 3593 80 crosslinking agents can be formed by reacting the polycarboxylic acid or its functional equivalent thereof with polyols at an elevated temperature usually reflux temperature in the presence of an.