Preparation of highly thermally stable and soluble ethylene-crosslinked ladder-like polymethylsiloxanes via template polymerisation

Abstract

In this study, ethylene-crosslinked ladder-like polymethylsiloxanes were prepared to achieve high polymer thermal stability and solubility. First, polysiloxane with diethoxymethylsilyl groups in its side chains was prepared via hydrosilylation between diethoxymethylsilane and polymethylvinylsiloxane. This polymer was then diluted in a mixed solvent of toluene and N,N-dimethylformamide (3 : 2, v/v). Subsequently, intramolecular polycondensation (template polymerisation) of the diethoxymethylsilyl groups was performed using purified water and hydrochloric acid as catalysts, affording ethylene-crosslinked ladder-like polymethylsiloxane (ECL-LPMS). Additionally, ECL-LPMS with trimethylsilyl-protected silanol groups (ECL-LPMS-TMS) was prepared by reacting the residual silanol groups in ECL-LPMS with chlorotrimethylsilane. Both polymers were soluble in various organic solvents. Solubility tests, gel permeation chromatography analysis, proton and silicon nuclear magnetic resonance spectroscopy, transmission electron microscopy and wide-angle X-ray diffraction measurement confirmed that the polymers featured a ladder-like structure comprising two polymethylsiloxane chains interconnected by ethylene linkages. Thermogravimetric analysis revealed high thermal stability, with 10% weight loss temperatures of 528 °C and 520 °C and residual weights of 81% and 65% at 800 °C for ECL-LPMS and ECL-LPMS-TMS, respectively. Ultraviolet–visible spectra of ECL-LPMS and ECL-LPMS-TMS cast films exhibited over 90% transmittance across a wide wavelength range (250–800 nm), indicating excellent transparency.