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The purpose of this study was to investigate the microstructural evolution and hydrolytic stability of poly(phenylborosiloxane) (PPhBS) to further use and develop the oligomers as heat-resistant modifiers.

PPhBS was synthesized by direct co-condensation of boric acid (BA) and phenyltriethoxysilane (PTEOS). The structural evolution of PPhBS at high temperature was investigated by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and 29Si nuclear magnetic resonance (NMR) spectroscopy. In addition, the change in the morphology of the PPhBS powder was examined to demonstrate the evolution of the chemical bonds, and the hydrolytic stability of PPhBS was investigated by a combination of X-ray diffraction (XRD) analysis, measurement of the mass loss in water and FTIR spectroscopy.

The results revealed that a cross-linking network was gradually formed with increasing temperature through the condensation of the residual hydroxyl groups in PPhBS, and the Si-OH and B-OH bonds remained even at a high temperature of 450°C. Furthermore, heat treatment improved the hydrolytic stability of the oligomer. The hydrolysis of the B-O-B bonds in PPhBS was reversible, whereas the Si-O-Si and Si-O-B bonds were highly resistant to hydrolysis.

The prepared PPhBS can be used as a heat-resistant modifier in adhesives, sealants, coatings and composite matrices.

Investigation of the structural evolution of a polyborosiloxane at high temperature by DRIFTS is a novel approach that avoided interference from moisture in the air. The insoluble mass fraction and the FTIR spectrum of PPhBS washed with water were used to investigate the hydrolytic stability of PPhBS.

In this paper, boric acid was loaded on the surface of expandable graphite (EG), polyvinyl alcohol (PVA) and silane coupling agent (KH550) served as a bridge. The purpose of this study was to improve the flame retardant properties of semi-rigid polyurethane, meanwhile, the mechanical properties of the foam got ameliorated.

PVA was dissolved in hot water. EG was added to this solution. After stirring for 0.5 h at 85°C in ultrasonic agitation, the system was put at room temperature to cool. The silane coupling agent KH550 was added dropwise into the solution system, stirring to fully hydrolyze. Boric acid was added into the system, placing it in an oven at 90°C to dry after filtration. Changing of flame retardant properties and mechanical properties of semi-rigid polyurethane adding modified EG were characterized.

The flame retardant performance of the foam with EG has been improved, whereas the tensile strength decreased with an increase in the content of EG. After adding modified EG, compared to semi-rigid polyurethane with EG, flame retardant performance and tensile strength of the foam improved.

In the study reported here, the surface of EG was modified by boric acid. The modified EG was added into semi-rigid polyurethane foam. The flame retardant performance and tensile strength of the foam after adding modified EG were discussed. Results of this research could benefit in-depth study of the influence of adding modified EG to semi-rigid polyurethane. The study could promote the application of flame-retardant polyurethane foam.

The flame retardant performance and tensile strength of the semi-rigid polyurethane were improved by adding modified EG. The effects of modified EG on the flame retardant performance and tensile strength of semi-rigid polyurethane were discussed in detail.