Radical Copolymerization of Vinylidene Fluoride with 8‐Bromo‐1H,1H,2H‐perfluorooct‐1‐ene: Microstructure, Crosslinking and Thermal Properties

Abstract

An original synthesis of 8‐bromo‐1H,1H,2H‐perfluorooct‐1‐ene (BDFO) and its radical copolymerization with vinylidene fluoride (VDF), initiated by 2,5‐bis(tert‐butylperoxy)‐2,5‐dimethylhexane at 134 °C, are presented. The fluorinated bromoalkene was obtained by dehydrobromination of 1,8‐dibromo‐1H,1H,2H,2H‐perfluorooctane in a satisfactory yield. Although BDFO did not homopolymerize under radical initiation, it did copolymerize with VDF. The compositions of the resulting random type copolymers were calculated by means of 19F NMR spectroscopy and allowed the quantification of the respective amounts of both comonomers in the copolymers, showing good incorporation of the brominated monomer. Nevertheless, obtaining PVDF copolymers containing a high molar percentage of BDFO in good yields was difficult to achieve from initial molar ratios of BDFO higher than 9.2 mol‐%. Radical terpolymerization of VDF, BDFO and hexafluoropropene (HFP) was also successfully achieved. BDFO contents in these co‐ or terpolymers ranged from 3.6 to 12.2 mol‐%. The bromoalkene acted as a cure site monomer and the resulting poly(VDF‐co‐BDFO) copolymers were crosslinked via the bromine atom in the presence of a triallyl isocyanurate/peroxide system. The materials obtained led to more thermally stable copolymers than the uncured ones and their thermostabilities were compared to those of commercially available poly(VDF‐co‐HFP) copolymers crosslinked using diamines.magnified image

Radical copolymerization of vinylidene fluoride with 1‐bromo‐2,2‐difluoroethylene

“…The glass transition temperature ( T g ) values of poly(VDF‐ co ‐BDFE) copolymers are close to −20 °C and comparable with those of poly(VDF‐ co ‐BDFO) copolymers 6. Obviously one exception, related to low‐molecular weight—from Exp.…”

“…These values of decomposition temperatures are lower than those of the poly(VDF‐ co ‐BDFO)6 copolymers, where BDFO stands for 8‐bromo‐1H,1H,2H‐perfluoroct‐1‐ene, for which the thermal decomposition occurred from 320 °C. This might arise either from the different nature of CBr bond (in the main chain of the copolymer for the present case and in the side chain for the other one), the influence of the molecular weight or from the amount of bromine in the copolymer, which is lower in poly(VDF‐ co ‐BDFO) copolymers than in poly(VDF‐ co ‐BDFE) copolymers.…”

“…This total solubility in such above solvents indicates that no crosslinking occurred in that copolymerization. Indeed, the conventional crosslinking reaction involving a bromine atom has already been observed in many works5–10 but, in that present case, it seems that the CBr bond is not activated enough to enable possible crosslinking (that should occur by recombination of macroradicals).…”

“…The glass transition temperature (T g ) values of poly(VDF-co-BDFE) copolymers are close to À20 C and comparable with those of poly(VDF-co-BDFO) copolymers. 6 Obviously one exception, related to low-molecular weight-from Exp. 7 (where M n ¼ 1,800 g/mol in equivalent polystyrene), shows a very low T g value (À47 C) (Supporting Information Figure S5).…”

“…That procedure induces good mechanical properties for different applications. Comonomers bearing bromine end atom(s) have already led to interesting crosslinkable copolymers, and few examples are the following: H 2 CCHCF 2 Br,4 H 2 CCHC 2 F 4 Br,5 H 2 CCHC 6 F 12 Br,6 F 2 CCFBr,7 F 2 CCFC 2 H 4 Br,8 F 2 CCFOC 2 F 4 Br,9 and F 2 CCFCF 2 Br 4. Several patents described the synthesis of these fluoroelastomers, the process for peroxide vulcanization, rendering them crosslinked elastomers or melt‐processible thermoplastic fluoropolymers, where only a small amount of halogen‐containing CSM was included in the copolymerization.…”