Stepwise cure and properties of silicone resin for high-ultraviolet-transmission optical elements

A new high-ultraviolet (UV)-transmission silicone-resin polymeric material was prepared via curing during hydrosilylation of tetramethyltetravinylcyclotetrasiloxane with tetramethylcyclotetrasiloxane by a liquid-surface supernatant method, using a stepwise heating program to avoid spontaneous combustion of the reaction mixture. The relationships were investigated in detail between reactive groups, cross-linking density, mechanical and UV-transmission properties. For this purpose, UV transmittance and dynamic mechanical properties, respectively, of the silicone resin were measured with UV-visible spectrophotometry and dynamic mechanical thermal analysis. In addition, surface roughness was evaluated with an atomic force microscope as well as an interferometer. The curing process was monitored by Fourier transform infrared spectroscopy and rotational rheometry. The cyclic silicone oils were compared with linear ones in structure and product properties. The results indicated that stepwise temperature control during curing process was particularly indispensible due to the presence of active SiH bonds, and that the silicone resin of high modulus, high UV transmittance (92.7%) and low surface-roughness was largely homogeneous in cross-linking points distribution. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43308.