Novel poly(tetramethyl-1,3-silphenylenesiloxane) derivative with phenol moiety in the main chain, that is, poly(tetramethyl-5-hydroxy-1,3-silphenylenesiloxane) (P1), was synthesized and the thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). P1 was obtained via deprotective hydrogenation of poly(tetramethyl-5-benzyloxy-1,3-silphenylenesiloxane) (Pre-P1) catalyzed by 10% palladium on charcoal as well as via direct polycondensation of 3,5-bis(dimethylhydroxysilyl)phenol (M2). Pre-P1 was obtained by polycondensation of 1,3-bis(dimethylhydroxysilyl)-5-benzyloxybenzene (M1), catalyzed by 1,1,3,3-tetramethylguanidinium 2-ethylhexoate. M1 was prepared by the Grignard reaction using chlorodimethylsilane and 1,3-dibromo-5-benzyloxybenzene followed by the hydrolysis catalyzed by 5% palladium on charcoal. M2 was prepared by deprotective hydrogenation of M1 catalyzed by 10% palladium on charcoal. The obtained P1 was soluble in common organic solvents such as tetrahydrofuran, chloroform, dichloromethane, toluene, and so forth as well as in highly polar solvents as ethanol and methanol in which poly(tetramethyl-1,3-silphenylenesiloxane) is insoluble. The glass transition temperature (T-g) of P1 was determined to be 40 degrees C from DSC, which was much higher than that of poly(tetramethyl-1,3-silphenylenesiloxane) (-52 degrees C), indicating that the intermolecular and/or intramolecular hydrogen bondings based on hydroxyl groups restricted the mobility of the main chain. The temperature at 5% weight loss (T-d5) Of P1 (393 degrees C) determined by TG was lower than that of poly(tetramethyl-1,3-silphenylenesiloxane) (ca. 500 degrees C), indicating that the phenol moieties decline the thermal stability; however, the obtained P1 would promise to be a new reactive-polymer with phenolic-hydroxyl moieties to develop new functional materials. (c) 2007 Wiley Periodicals, Inc.