Postcure behavior of UV curable materials: A comparison of urethane acrylates with vinyl ether end-capped urethanes.

Abstract

The study presented here examines the effect of postcure on the mechanical properties of urethane acrylates as compared to vinyl ether functionalized polyurethanes. The vinyl ether systems cure via a cationic mechanism and are, therefore, expected to undergo dark reactions which may lead to noticeable postcure effects. Urethane acrylate systems, on the other hand, are not known to undergo postcuring reactions since these systems polymerize via the free radical mechanism. Recently, however, it has been reported that trapped free radicals exist in irradiated acrylate samples for periods as long as seventy days [1], and that radical entrapment occurs very early in the reaction at conversions as low as 10% [2] . It has also been reported that acrylate unsaturation continues to disappear for several days after irradiation [3]. These findings, important as they are, only reflect the spectroscopic behavior of UV cured acrylates using electron spin resonance and infrared absorption techniques. Although some studies relating mechanical property changes to postcuring of acrylate systems have been reported [4], no clear correlation between these parameters has been identified [5]. The comparative data reported here helps identify the effects and the nature of the postcuring process in both the acrylate and the vinyl ether systems.