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Synthesis and Properties of Polyphenylsilsesquioxane Modified Phenolic Resin by in-situ Polymerization from Phenyltriethoxysilane Precursor

ABSTRACT A series of phenolic resin-polyphenylsilsesquioxane (PR-PPSQ) composites were prepared by in situ formation from phenyltriethoxysilane (PTES) precursor during polymerization of the PR. The precursor was firstly hydrolyzed in a solution, and then the sol was added to the PR polymerization system. The structures of the composites were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and solid-state 29Si nuclear magnetic resonance (Si-NMR). The PPSQs were spherical particles with a diameter of about 3 µm and nearly uniformly dispersed in the matrix, as revealed by scanning electron microscopy (SEM). The influence of PTES content on the thermal behavior of the PR was characterized by thermogravimetric analysis (TGA) in nitrogen and air atmospheres. The results showed that the onset temperature and residual weight of the composite containing 20 wt% PTES content were improved by 47°C and 8.4%, respectively, compared to the pure PR. The thermal oxidative stability was also greatly increased; the 50 wt% weight loss temperature rose from 567°C for PR to 601°C. The flexural strength of the composites was improved; in particular, the value of the composite containing 15 wt% PTES content was elevated by 32% (from 41.66 to 55.33 MPa).