| abstract |
A prepolymerization step prior to casting reduces shrinkage during polymerization of a composition containing diethylene glycol bis(allyl carbonate) with up to 40% of a vinyl ester, preferably vinyl acetate, and one or more free radical type initiators. The prepolymerization step includes adding a small amount of free radical type initiator, which may be the same or different than that used just prior to casting, and heating to a temperature higher than one hour half-lifetime temperature of the initiator. In this manner, most of the added initiator is consumed and the prepolymerization produces the highest possible conversion while preventing overpolymerization. High yield of lenses of ophthalmic quality is obtained. |