Résumé
Fluorinated polymers are high value-added materials with exceptional properties (e.g. thermal stability, chemical inertness, low values of the refractive index, permittivity, dissipation factor and water absorption as well as excellent weather durability and resistance to oxidation) for various applications: aeronautics, microelectronics, engineering, chemical industry, optics, textile finishing, automobile industry and wiring. Among them, fluoroelastomers are quite interesting. This presentation reports the synthesis, characterization and crosslinking of those made of vinylidene fluoride (VDF) and perfluoromethyl vinyl ether (PMVE), by iodine transfer copolymerization in the presence of a telechelic diiodoperfluoroalkane chain transfer agent (CTA), IC6F12I or IC4F8I, using an emulsion process without any surfactant. The copolymer compositions, molecular weights, and end-groups of these random copolymers were assessed by means of 19F NMR spectroscopy. The CTA concentration enabled one to control the molecular weights of the resulting telechelic diiodo-poly(VDF-co-PMVE) copolymers ranging from 1,000 to 18,000 g mol-1. In addition, the thermal properties, i.e. the glass transition temperatures, Tgs, ranging from -63 to -35 °C, and the degradation temperatures (greater than 250 °C under air), of these copolymers were found to depend on the molecular weights and on the monomer composition of the copolymers. Two major strategies were applied to obtain poly(VDF-co-PMVE) copolymers based diols as precursors of bis(acrylate)s containing various spacer lengths between hydroxyl (or ester functions) and the poly(VDF-co-PMVE) oligomeric chain. The first approach involved quantitative ethylene end-capping of telechelic diiodo poly(VDF-co-PMVE) copolymer and subsequent hydrolysis to form diols with ethylene spacers (C2) between -OH moieties and the fluorinated oligomeric chain. The second pathway to obtain fluorinated diols involved the radical addition of telechelic poly(VDF-co-PMVE) copolymer onto allyl alcohol to obtain bis(iodohydrine), the iodine atoms of which were further reduced to yield fluorinated diols (85 % yield) that bear three methylene groups (C3) as the spacer. Acrylation of C2 diol was optimized from various acrylating agents and catalysts (75 % yields) and was monitored by IR spectroscopy. The acrylation of C3 diols was carried out using acryloyl chloride and taking into account the results from C2 optimization (85 % yields). UV curing of C2 and C3 telechelic bis(acrylate)s led to crosslinked films, the gel contents, flexibilities (via the assessment of their glass transition temperatures that ranged between -53 and -30 °C) and thermal behavior (their 10 wt.% losses were ranging between 240 and 360 °C, under air) were investigated.