Structural control of silane-grafted polymethylsilsesquioxane

This study presents the preparation and fabrication of a series of silane-grafted polymethylsilsesquioxane (SGPMSQ) with a controllable structure and molecular weight. The results of FTIR analysis show that synthesizing polymethylsilsesquioxane (PMSQ) with methyltriethoxysilane (MTES) formed a regular structure such as the cage or ladder structure. The results of XRD and FTIR analysis show that the molecular structure started to change from regular to an irregular random network structure after grafting with tetraethoxysilane (TEOS) and 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTS) on the PMSQ. The changes in the molecular structure of SGPMSQ created by grafting silane are similar to the changes in the molecular structure of PMSQ film heated from 150 to over 250 °C, reducing the refractive index (RI). The RI of PMSQ at 583 nm decreased from 1.50 to 1.42 merely by heating it to 80 °C, introducing silane, and controlling the molecular structure. When the weight ratio of MTES:TEOS:PFDTS was 1:0.5:1, the decomposition temperature (Td) of SGPMSQ was 340 °C, which is much higher than that of pure PMSQ (Td = 267 °C). Although the glass transition temperature of SGPMSQ was 20 °C lower than that of pure PMSQ, its decomposition temperature was 73 °C higher. This shows that SGPMSQ is more flexible and has greater thermal stability than pure PMSQ.