and aromatic diisocyanates are preferred as they provide better heat resistance polyols can be diols or triols diols are preferred as they produce linear structure which are flexible and not gelled in polymer solution examples of polyols include but are not limited to ethylene glycol propylene glycol butanediol hexanediol cyclohexanedimethanol polyethylene glycol polypropylene glycol poly teramethylene ether glycol and polycaprolactone diol the preferred molecular weight of diol is in the range of about 100 to about 3000 about 500 to about 2500 or about 1000 to about 2000 examples of carboxylic polyols include but are not limited to dimethylolbutanoic acid and dimethylolpropionic acid the acid value of resultant polyurethane is preferably about 30 mgkoh g to about 110 mgkoh g examples of hydroxyl meth acrylates include but are not limited to 2 hydroxyethyl meth acrylate 2 hydroxypropyl meth acrylate 4 hydroxybutyl meth acrylate and phenylglycidylether meth acrylate in some embodiments to avoid polymerization of acrylate group thermal polymerization inhibitors can be added examples of inhibitors include but are not limited to hydroquinone alkyl and aryl substituted hydroquinones and phenothiazine in the photosensitive coverlay composition compound a is from about 20 to about 90 by weight preferably from about 40 to about 70 by weight based on total solid mass of composition the compound b is a mono or multi functional meth acrylate monomer or oligomers which are used to enhance photosensitivity among them multi functional meth acrylates are preferred.