Two disilanol monomers containing perfluorocyclobutane rings, 1,2-bis[4-(dimethylhydroxysilyl)phenoxy] butane and 1,2-bis[3-(dimethylhydroxysilyl)phenoxy] were prepared and self-polymerized by treatment with base. The glass transition temperatures (T(g)s) of the two high-molecular-weight polymers obtained were 27 and -12 degrees C, respectively. The two monomers were also copolymerized with an alpha,omega-silanol-terminated 3,3,3-trifluoropropylmethylsiloxane (fluorosilicone) oligomer to form copolymers with varying compositions. The T(g)s of the copolymers, which ranged from -60 to -1 degrees C, increased as the amount of the perfluorocyclobutane-containing silphenylene repeat units increased. Copolymers containing more than 20 wt% of this repeat unit displayed less weight loss at elevated temperatures than a fluorosilicone homopolymer when subjected to isothermal gravimetric analysis. One of the copolymers, which contained about 30 wt% of the perfluorocyclobutane-containing repeat unit, was crosslinked with 2,4-dichlorobenzoyl peroxide. The crosslinked network displayed a volume swell of under 40% in isooctane, similar to a crosslinked fluorosilicone. (C) 2000 Elsevier Science Ltd. All rights reserved.