Thermal and optical properties of highly fluorinated copolymers of methacrylates

Copolymers of pentafluorophenylhexafluoroisopropyl methacrylate (FPPMA) with trifluoroethyl methacrylate (TFEMA) were prepared in THF solution and in bulk using azobisisobutyronitrile as a free radical initiator. The monomer reactivity ratios of TFEMA (M₁) and FPPMA (M₂) were calculated as r₁=0.55 and r₂=0.07. The refractive indices of poly(TFEMA) and poly(FPPMA) are very similar as 1.435 and 1.430, respectively, at 532nm, and the copolymer films were transparent. The glass transition temperatures (T_g) of the copolymers were in the range of 80-90°C and showed a negative deviation from the Gordon-Taylor equation. The thermal decomposition temperature (T_d) was increased with the content of FPPMA in copolymers. Low water absorption for 1:1 FPPMA/TFEMA copolymer was detected. Copolymers of FPPMA with hexafluoroisopropyl methacrylate (HFPMA) were also prepared. The monomer reactivity ratios of HFPMA (M₁) and FPPMA (M₂) were calculated as r₁=0.43 and r₂=0.10. The T_gs of the copolymers were in the range of 88-95°C and showed also a negative deviation from the Gordon-Taylor equation. T_g and T_d of the copolymers were increased with the content of FPPMA. The refractive index of poly(HFPMA) (1.384 at 532nm) is much lower than that of FPPMA homopolymer, but copolymer films obtained were clear and transparent.