Synthesis and Polymerization of Fluorinated Monomers Bearing a Reactive Lateral Group-Part 7.Copolymerization of Tetrafluoroethylene with #omega#-Hydroxy Trifluorovinyl Monomers

摘要

The radical copolymerization of tetrafluoroethylene (TFE) and triflurovinyl #omega#-hydroxy comonomers [F_2C velence CF(CH_2)_m OH with m=1 (FA1) and m=3 (FA3)] for the synthesis of fluorinated polymers bearing hydroxy side groups is presented. FA1 was prepared by dehydrofluorination of 2,2,3,3-tetrafluoropropanol, whereas FA3 was obtained in a three-step scheme starting from the radical addition of 1,2-dichloroiodotrifluoroethane to allyl alcohol. The copolymerization conditions (in bulk or in solution in di n-butyl ether) and the polymer compositions considerably influenced the molecular weights, the molecular weight distributions, and the thermal properties of these copolymers. The kinetics of copolymerization of both couples enabled to determine the reaction order to the initiator (being 0.9) and the close values of apparent activation energies for [TFE/FA1 (E_a=52.4 kJ centre dot mol~(-1)) and for TFE/FA3 (E_a=46.8 kJ centre dot mol~(-1))] couples. From the Todwell and Mortimer method, the relative reactivity ratios were calculated by elemental analysis of by ~19F-NMR spectroscopy, showing a higher reactivity of the TFE to incorporate the copolymer (r_TFE=2.47 and r_FA1-0.41; r_TFE=1.57 and r_FA3=0.45). The high values of reaction order to the initiator and low molecular weights of copolymers were associated to the allylic chain transfer of the hydroxy comonomers and a mechanism of copolymerization was proposed. The comonomer diad triad distribution was determined by the statistic theory and allowed one to calculate the average length of the comonomer sequences. Finally, the thermal decomposition of these cooligomes showed that those containing FA3 units are more thermostable than those synthesized from FA1, and that the higher the fluorinated aldohol content, the faster the thermal decomposition.