n integer of 0 to 10, R1 is CH3 or hydrogen atom, X is an alkyl group or hydroxyalkyl group which has 1-5 carbon atoms respectively; pentaerythritol tetra(meth)acrylate, 1,6-hexanediol di(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate and the like; a compound represented by the general formula: ##STR3## where Z is ##STR4## R1 is as defined above, and m i