Aryl‐groupsubstituted polysiloxanes with high‐optical transmission, thermal stability, and refractive index

Polysiloxanes are an important class of polymers for optoelectronic applications. Novel polysiloxanes with high‐refractive index (RI) based on phenanthrenyl‐substituted monomers are prepared by a polycondensation reaction starting from various substituted dialkoxysilanes as monomers. The substitution patterns on the Si atom are systematically changed to vary the properties of the linear polymers as well as the final cured material. The two monomers with polycyclic aromatic side groups 9‐phenanthrenylmethyldimethoxysilane and 9‐phenanthrenylphenyldimethoxysilane are synthesized and fully characterized, including their single crystal X‐ray structures. Linear polysiloxanes with variations in hydride, methyl, vinyl, phenyl, and phenanthrenyl side group content are prepared by acid‐ and base‐catalyzed polycondensation reactions. Both SiH and Si vinyl substituted polymers with molecular weights up to 30 kDa and adjustable RI's from 1.52 to 1.63 are obtained and the thermally cured by Pt‐catalyzed hydrosilylation reactions. Polysiloxane resins are obtained with high‐RI's, optical transmittance above 95% and thermal stabilities up to 420°C. Long‐term thermal stability tests show transmittance values above 85% even after 60 days of thermal treatment at 180°C.