Novel polysiloxane derivative having adamantyl moiety in the main chain (PI) was synthesized and characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), and X-ray diffraction analysis. P1 was obtained by bulk polycondensation without catalysts as well as solution polycondensation of novel disilanol monomer, i.e., 1,3-bis[4-(dimethylhydroxysilyl)phenyl]adamantane (M1), which was prepared by the Grignard reaction using chlorodimethylsilane and 1,3-bis(4-bromophenyl)adamantane, followed by the hydrolysis catalyzed by 5% palladium on charcoal. The molecular weight of P1 was dependent on the concentration of M1 in solution polycondensation, and the high concentration of M1 would result in the high average molecular weight of P1. P1 exhibited the good solubility in common organic solvents, such as tetrahydrofuran (THF), chloroform, dichloromethane, and toluene. The glass transition temperature (T-g) of P1 determined from DSC would be dependent on the average molecular weight of P1. The highest T-g was 115 degrees C and much higher than that of poly (tetramethyl-1,4-silphenylenesiloxane) (-20 degrees C). The melting temperature (T-m) of P1 seemed to be independent of the average molecular weight of P1 and was in the range of 153-157 degrees C, which was comparable to the T-g of poly(tetramethyl-1,4-silphenylenesiloxane). The temperature at 5% weight loss (T-d5) of P1 determined by TG was also comparable to that of poly(tetramethyl-1,4-silphenylenesiloxane), indicating that P1 is a new polysiloxane derivative with the high T-g as well as good thermostability. (C) 2008 Elsevier Ltd. All rights reserved.