Thermomechanical behavior of poly(carborane–siloxane)s containing CB5H5C cages

Abstract

AbstractThe thermomechanical spectra of two new carborane–siloxane polymers containing five‐boron carborane cages in the backbones are reported and discussed. The polymers are the homopolymer, HO[Si(CH3)2CB5H5CSi(CH3)2O]nH, and the random copolymer with 20 mole‐% of the ten‐boron meta‐carborane analogue, [Si(CH3)2CB10H10CSi(CH3)2O]. The mechanical spectra (∼1 cps) were determined from −180° → +625° → −180°C (ΔT/Δl = 3.6°C/min for T > 25°C and 2°C/min for T < 25°C) using the semimicro thermomechanical technique, torsional braid analysis. In nitrogen, both polymers displayed secondary transitions at −140°C. The glass transition (Tg) for the homopolymer was −60°C and for the copolymer was −52°C. The homopolymer had a melting point of +70°C. The copolymer was amorphous. The high‐temperature stability in nitrogen of both polymers appeared to be identical; thermal stiffening commenced at 400°C, continued to 625°C, and resulted in materials that were typical of highly crosslinked resins. In air, the homopolymer began to stiffen catastrophically near 270°C, while the copolymer began to stiffen similarly nearly 50°C higher. The intrinsic elastomeric nature together with the thermomechanical results prompted further study of the copolymer. Thermomechanical cycling studies in nitrogen and air are reported for the copolymer. Some correlating TGA and DTA are also discussed.