Synthesis and thermal properties of fluorosilicones containing perfluorocyclobutane rings

Two disilanol monomers containing perfluorocyclobutane rings, 1,2-bis[4-(dimethylhydroxysilyl)phenoxy]-1,2,3,3,4,4-hexafluorocyclobutane and 1,2-bis[3-(dimethylhydroxysilyl)phenoxy]-1,2,3,3,4,4-hexafluorocyclobutane, were prepared and self-polymerized by treatment with base. The glass transition temperatures (Tgs) of the two high-molecular-weight polymers obtained were 27 and −12°C, respectively. The two monomers were also copolymerized with an α,ω-silanol-terminated 3,3,3-trifluoropropylmethylsiloxane (fluorosilicone) oligomer to form copolymers with varying compositions. The Tgs of the copolymers, which ranged from −60 to −1°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-dichlorobenzoylperoxide. The crosslinked network displayed a volume swell of under 40% in isooctane, similar to a crosslinked fluorosilicone.