o phenylphenol glycidyl ether and so on of these compounds o phenylphenol glycidyl ether is a compound of the formula str2 the reaction mole ratio of b to a in terms of nco oh is 0 1 u02dc 2 0 preferably 0 8 u02dc 1 2 the weight ratio of a to c is preferably selected within the range of 60 40 u02dc 90 10 when the proportions of these components are controlled as above the reaction product most suited for the purposes of the invention is obtained when d is used its ratio to a is suitably not over 30 weight percent preferably 10 u02dc 25 weight the combined use of d is instrumental in improving the refractive index of the product but an excess of d may detract from the resistance of the product to heat solvents and impact the above components may be pre polymerized in the presence of a polymerization initiator nco oh reaction catalyst ultraviolet absorber antioxidant antistatic agent dye stabilizer etc and the reaction product be then poured in a casting mold after removal of dissolved gases the mold is heated to initiate a curing reaction whereby the desired three dimensional reaction product can be obtained it should be understood that the above pre polymerization step may be sometimes omitted the polymerization initiator includes inter alia lauroyl peroxide benzoyl peroxide p chlorobenzoyl peroxide 2 4 dichlorobenzoyl peroxide diisopropyloxy carbonate di 2 ethylhexyl peroxycarbonate t butyl peroxypivalate azobisisobutyronitrile azobis 2 4 dimethylvaleronitrile azobiscyclohexane nitrate and so on the proportion of the polymerization.