Jérôme Guiot

Synthesis and polymerization of fluorinated monomers bearing a reactive lateral group 13. Copolymerization of vinylidene fluoride with 2-benzoyloxypentafluoropropene☆

Abstract The synthesis of 2-benzoyloxypentafluoropropene (BPFP) and its radical copolymerization with vinylidene fluoride (VDF), initiated by tert-butyl peroxypivalate is presented. In a first step, the preparation of two monomers [F2CC(CF3)OCOR were R stands for CH3 or C6H5] was attempted. In contrast to the acetoxy derivative that could not be isolated, the benzoyl monomer was purified and then copolymerized with VDF. A series of 11 copolymerization reactions was achieved starting from initial [VDF]0/([BPFP]0+[VDF]0) molar ratios ranging from 19 to 99 mol%. The molar compositions of the obtained copolymers were assessed by means of 19F nuclear magnetic resonance spectroscopy. From the Tidwell and Mortimer method, this kinetics of copolymerization led to the determination of the reactivity ratios, ri, of both comonomers (rVDF=0.77±0.40 and rBPFP=0.11±0.32). Hence, the Alfrey and Price equation enabled one to assess the Q and e parameters of BPFP as follows: 0.019 (from QVDF=0.008), 0.043 (from QVDF=0.015) or 0.182 (from QVDF=0.036) and 1.97 (vs eVDF=0.40), 2.07 (vs eVDF=0.50) or 2.77 (vs eVDF=1.20), respectively. These Q–e parameters and ri were compared to those of other fluoroalkenes and are discussed.

Synthesis of fluorinated telomers

Radical telomerizations of 1,1-difluoro-2-chloroethylene and 1,2-difluoro-1,2-dichloroethylene with methanol, leading to chlorofluoroalcohols, are presented. The optimization of the synthesis conditions led to 3-chloro-2,2-difluoropropanol and 2,3-dichloro-2,3-difluoropropanol in 80% and 89% conversion, respectively, much higher than those reported in the literature. The best conditions were achieved when 2,5-bis(tert-butylperoxy)-2,5–dimethylhexane (DHBP) was used as the initiator at 407 K with an initial ([MeOH]0/[alkene]0) molar ratio, R0, of 40. The unsymmetrical alkene led to one isomer only, in contrast to the formation of two isomers from chlorotrifluoroethylene. Furthermore, this study has shown the influence of the fluorine and chlorine atoms of the olefin in directing the radical reaction. Hence, by its polar and steric effects, the chlorine atom in these alkenes does not favor the radical addition of HOCH2˙. In contrast, the inductive effects of the fluorine atom increase the reactivity of the hydroxymethyl radical. A decreasing reactivity series of different chlorofluoroolefins with respect to the radical addition of methanol is proposed with the optimal conditions for each telomerization: F2CCCl2 > F2CCFCl > ClCFCFCl > F2CCHCl and an overall reactivity series of different fluoroalkenes with methanol is also suggested.

Synthesis of fluorinated telomers. Part 6. Telomerisation of chlorotrifluoroethylene with methanol

Bulk radical telomerisation of chlorotrifluoroethylene (CTFE) with methanol was investigated for the synthesis of fluorinated alcohols. Improvements in the conversion of CTFE and of the selectivity of the reaction were sought by using different radical initiators (peroxides, percarbonates, peresters) and an excess of methanol. These reactions were compared in terms of CTFE conversion, yield of monoadduct and formation of higher molecular weight telomers. Under these conditions, radical initiated telomerisations systematically led to low molecular weight CTFE telomers. 2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane (DHBP) proved to be the most effective radical initiator. All these experiments revealed the low chain transfer activity of methanol in the presence of CTFE. A thorough structural study of typical CTFE–methanol telomers was performed by 19F, 1H and 13C NMR spectroscopies. These analytical methods allowed us to prove the highly regioselective formation of HOCH2CF2CFClH (produced with a 95% selectivity), showing the regioselectivity of the addition of hydroxymethyl radicals onto the difluoromethylene side of CTFE.