Synthesis and characterization of vinyl-terminated copolysiloxanes containing 3,3,3-trifluoropropyl groups

Abstract

A series of fluorosilicones containing various amounts of 3,3,3-trifluoropropyl (TFP) [–CH₂CH₂CF₃] and vinyl groups were synthesized by ring-opening copolymerization of dimethylcyclosiloxane (D_n), 1,3,5-tris(3,3,3-trifluoropropyl)-1,3,5-trimethylcyclotrisiloxane (F₃) and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V₄). These fluorosilicones were characterized by GPC, ¹H NMR, ²⁹Si NMR, DSC and rotational viscometry. GPC analysis showed that the polydispersity of the polysiloxanes became narrower when the feeding amount of F₃ was increased. FTIR, ¹H NMR and ²⁹Si NMR analyses confirmed that the amount of TFP containing unit (F unit) in the polysiloxane grew with the increase in F₃ feeding amount in the preparation process. The results of ¹H NMR and ²⁹Si NMR showed that the composition of each copolymer was almost equal to the feed ratio, and the sequence distributions of each polysiloxane followed random statistics. The random incorporation of an F unit into the polydimethylsiloxane (PDMS) chain resulted in the disappearance of melting peaks at −45.7 and −34.8 °C which were observed in the DSC curve of PDMS. Also, the glass transition temperatures (T_g) of the copolysiloxanes increase with the F unit content, but have little relationship with the concentration of CH₂CHSi(CH₃)O. As shown by rheological tests, incorporation of F units also increased the viscosity of the copolymers. The oil resistance tests showed that the introduction of –CH₂CH₂CF₃ groups greatly improved the oil resistance of the silicone rubber.