Synthesis of telechelic methacrylic siloxanes with cycloaliphatic substituents groups for UV-curable applications

Methacrylic functionalized siloxanes were prepared in a two-step process. In the first step, a series of telechelic glycidyl epoxy siloxanes were prepared, substituted with either methyl, cyclopentyl, or cyclohexyl groups. In the second step, the telechelic glycidyl epoxy groups were reacted with methacrylic acid. The reaction was monitored via acid value, and when the acid value was ?10, the reaction was terminated. Characterization of the methacrylic telechelic siloxane polymers were performed using ¹H NMR, ¹³C NMR and FT-IR. The methacrylated siloxanes were formulated with a free radical photo-initiator, UV-cured, and the rate of polymerization was monitored via photo-differential calorimetry. After curing, viscoelastic properties, and oxygen-permeability were evaluated. In addition, X-ray was used to evaluate the structure of the cured films. The rate of polymerization was dependent on substituent and increased with increasing substituent size. The oxygen permeability was dependent on crosslink density, and increased with increasing substituent size. The increase in permeability, and thus free volume was supported by X-ray studies which showed an increase in d-spacing with increasing alkyl size.