Synthesis of Cycloaliphatic Substituted Silane Monomers and Polysiloxanes for Photo-Curing

A synthetic scheme was developed to prepare cationically polymerizable methyl, cyclopentyl, and cyclohexyl substituted polysiloxanes. Initially, the desired cycloalkene and dichlorosilane were reacted at high pressure (approximately 250 psi) and high temperature (120 °C) to yield the desired cycloaliphatic dichlorosilane. The chlorosilane monomers underwent an oligomerization to produce cyclic oligomers of low molecular weight (2000 g/mol). Polysiloxanes were produced through the acid-catalyzed ring-opening polymerization of the cyclic oligomers to yield high molecular weight polysiloxanes (45 000 g/mol). The polysiloxanes were then functionalized with a cycloaliphatic epoxy and alkoxysilane groups via hydrosilylation. Monomers, oligomers, and polymers were characterized by 1H and 29Si NMR, FT-IR, and electrospray ionization mass spectroscopy. The photoinduced curing kinetics and activation energies were investigated using photodifferential scanning calorimetry. Differential scanning calorimetry was used in order to observe any physical changes in the films that are brought about due to the variation of the pendant groups. The cycloaliphatic substituents raised the glass transition temperature and affected the curing kinetics when compared to a methyl substituted polysiloxane. The activation energies were found to be 144.8 ± 8.1 kJ/mol for the methyl substituted and 111.0 ± 9.2 and 125.7 ± 8.5 kJ/mol for the cyclopentyl and cyclohexyl substituted polysiloxanes