Rapid Solid-State Photopolymerization of Cyclic Acetal-Containing Acrylates

A cyclic acetal-functionalized urethane acrylate monomer is synthesized here and polymerized in a crystalline state without the polymerization kinetics being deleteriously affected by the solid state. Depending on the processing conditions, the cyclic acetal urethane acrylate monomer exists in either a metastable liquid state or a crystalline state at ambient conditions. Because of mobility restrictions, extremely poor polymerization kinetics and functional group conversions are typically achieved in solid-state polymerizations. However, the solid-state photopolymerization of a cyclic acetal urethane acrylate results in nearly identical polymerization rates and ultimately higher conversion in the crystalline state than in the liquid state under otherwise identical conditions. We conclude that the crystallization process occurs in such a manner as to template the acrylic double bonds in a structure that facilitates rapid, minimally activated propagation.