Synthesis of Mixed Ladder-Like Polysilsesquioxanes by Copolymerization of 2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane and Dodecyltrimethoxysilane

Epoxycyclohexyl- and dodecyl-bearing ladder-like polysilsesquioxanes (EDLASQs) are synthesized through the hydrolysis of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (ECTMS) and dodecyltrimethoxysilane (DTMS) and co-condensation of their hydrolysates. Such copolymerization reactions are traditionally conducted in tetrahydrofuran and water containing K₂CO₃ as the catalyst. The differing water compatibilities of the two monomers cause their reaction rates to differ drastically, making their random copolymerization questionable. In this work, we demonstrate that the reaction rates of the more hydrophobic DTMS monomer can be increased by adding a surfactant, either sodium dodecyl sulfate or cetyltrimethylammonium bromide, which increases the dispersion of the aqueous phase in monomers and the area of the monomer/water interfaces. Due to the homogenized hydrolysis rates of ECTMS and DTMS, the EDLASQ prepared in the presence of a surfactant possesses E/D molar ratios close to the ECTMS-to-DTMS feed molar ratio even at the early stages of their copolymerization. In contrast, EDLASQ prepared without a surfactant is enriched with E at earlier polymerization times, suggesting the blocky nature of the produced copolymers. Coating samples of an EDLASQ at an E/D molar ratio of 8/1 prepared using the new method exhibit high light transmission (99.9% at 600 nm after substrate absorption correction), high hardness (1.26 GPa), and enhanced water repellency. The proposed method is general and should be useful for the synthesis of other random co-LASQs.