Novel Method to Assess the Molecular Weights of Fluoropolymers by Radical Copolymerization of Vinylidene Fluoride with Various Fluorinated Comonomers Initiated by a Persistent Radical

Abstract

Batch radical homopolymerization of vinylidene fluoride (VDF) and its copolymerizations with seven fluorinated comonomers such as H 2 CCR A CF 3 (where R A stands for H, F, CO 2 R (R = H or tBu) or F 2 CCFR B (R B : H, CF 3 , OCF 3 ) initiated by • CF 3 radical generated from a perfluoro-3-ethyl-2,4-dimethyl-3-pentyl persistent radical (PPFR) are presented. That highly perfluorinated branched radical itself was unable to directly initiate the copolymerization in contrast to the generated trifluoromethyl radical that was successful. The microstructures of the resulting PVDFs, poly(VDF-co-H 2 CCR A CF 3 ) or poly(VDF-co-F 2 CCFR B ) (co)polymers were assessed by 19 F and 1 H NMR spectroscopy. 19 F NMR spectra displayed a quintet centered at −61 ppm assigned to a CF 3 end-group which enabled one to determine both the molecular weights of the resulting (co)polymers and the amounts (numbers and molar percentages) of these above comonomers. In all cases, the regioselective radical addition of • CF 3 onto the methylene site of VDF was noted as well as for 3,3,3trifluoropropene. In addition, the 19 F NMR spectra showed the absence of signals attributed to PPFR or its derivatives. According to [PPFR] o /([VDF] o + [comonomers] o ) initial molar ratios, this novel initiating system could produce high molecular weight-fluoropolymers (up to 200 000 g•mol −1 ). The lower that ratio, the higher their molecular weights as well as the higher their thermal stability (a 10% weight loss under air was noted at 425 °C). Although the kinetics of radical copolymerization were not studied, the presence of branched persistent radical did not disturb the reactivities of the comonomers and it was not involved in the primary recombination of radicals in the termination step of the polymerization while the macromolecular recombination was favored. For an initial PPFR concentration lower than 1 mol %, a feed ratio of ca. 20 mol % of 2-trifluoromethacrylic acid, MAF (or tert-butyl 2-trifluoromethacrylate, MAF−TBE) led to alternated poly(VDF-alt-MAF or MAF−TBE) copolymers. High yields (90%) of copolymers based on VDF and 2,3,3,3-tetrafluoroprop-1-ene, hexafluoropropylene (HFP), or perfluoromethyl vinyl ether (PMVE) comonomers were achieved while those from MAF, MAF−TBE, trifluoroethylene, and 3,3,3-trifluoropropene were fair to satisfactory. As expected, for a reasonable amount of HFP and PMVE inserted in the copolymers (>18 mol %), elastomers endowed with low T g values (−35 and −42 °C, respectively) were produced. In addition, the higher the content of VDF, the lower the T g , though the presence of tBu from MAF−TBE slightly increased the T g values. Copolymers containing MAF or MAF−TBE exhibited poor thermostability (that arises from the decarboxylation and isobutylene elimination from MAF or MAF−TBE, respectively) in contrast to the other VDF-containing copolymers that showed decomposition from 250 °C under air.

Radical copolymerisation of chlorotrifluoroethylene with isobutyl vinyl ether initiated by the persistent perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical

“…The literature 10,13 indicates that, if the polymerisation occurs in a regioselective way via path 1a, there should be only one 19 F NMR signal for CF 3 , centered at -63 ppm.…”

“…The synthesis of fluorinated copolymers specially designed to overcome the problematic properties of the homopolymers has been the focus of extensive research. 4,8,9 Recently Patil et al 10 utilised the persistent perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical (abbreviated as PPFR 11 , structure shown in Figure 1) to generate •CF 3 radicals for polymerisation initiation. The resulting CF 3 end groups were used in 19 F NMR spectroscopy for the determination of average molecular weights of VDF copolymers.…”

Mn2(CO)10-photomediated synthesis of poly(vinylidene fluoride)-b-poly(styrene sulfonate)

“…Indeed, to date there is no evidence of the reversible activation of the ''bad'' PVDFACF 2 ACH 2 AY chain ends, and the only current approach to FM-CRP, remains the iodine degenerative transfer [15,[36][37][38][39][40][41] (IDT: P Å n þ P m AI P n AI þ P Å m ) [7][8][9][10][11][12][13]42]. Nonetheless, addition fragmentation CRP methods may afford some level of control especially in VDF copolymerizations [43][44][45][46].…”

Enhancement of surface properties on Low Density Polyethylene packaging films using various fluorination routes

“…Different components resulted from different neighbouring around ACHFA or ACF 2 A groups, e.g. CH 2 ACHFACH 2 , CH 2 ACHFACHF, CH 2 ACHFACF 2 , CHFACHFACHF, CF 2 ACHFACF 2 [41][42][43][44].…”