SYNTHESES AND PROPERTIES OF UV-AUTOCURABLE PREPOLYMERS - SEMICRYSTALLINE URETHANE-MULTIACRYLATES

A series of UV-autocurable urethane-multiacrylate prepolymers, which were semicrystalline and showed melting points in the region of 40-50-Degrees-C, was synthesized. Also, the effects of curing temperature and acrylic functionality on the structure and properties of the cured films were investigated. These prepolymers are solids and opaque at room temperature. In general, UV curing reactions of solid prepolymers are less efficient when compared with those of liquid prepolymers. UV curing reactions at curing temperatures below the melting point (T(m)) of the prepolymers produced semicrystalline urethane-multiacrylate cured films. On the contrary, UV curing reactions above T(m) destroyed the crystalline phase of the prepolymers and improved the transparency of the cured films. The films cured below T(m) of the prepolymers had higher both breaking strength and Young's modulus, and a higher glass transition temperature (T(g)), but a lower elongation at break than those cured above T(m). Such curing temperature effects were attributed to the retention or disappearance of the crystalline structure of the prepolymers during UV curing reaction. At curing temperatures below T(m), an increase in acrylic functionality of the prepolymer resulted in a fast curing rate and a higher crosslinking density of the cured films. Therefore, an increase in acrylic functionality of the prepolymers gave cured films with higher breaking strength and Young's modulus, but a lower elongation at break.