Abstract
Novel telechelic primary diols and diacrylates based on vinylidene fluoride (VDF) and perfluoromethyl vinyl ether (PMVE) were synthesized as precursors of original photocrosslinkable networks. First, poly(VDF-co-PMVE) copolymers were generated by controlled radical copolymerization of VDF and PMVE in the presence of -diiodoperfluorobutane, leading to copolymers with molecular weight ranging between 1500 and 7000 g.mol-1. Then, two major approaches were applied to obtain telechelic poly(VDF-co-PMVE) diols as precursors for bis(acrylate)s containing spacers of various lengths between hydroxyl or ester functions and the poly(VDF-co-PMVE) oligomeric chain. The first strategy 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 approach to obtain fluorinated diols involved the radical addition of telechelic diiodo 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 between -OH moieties and the fluorinated chain. Acryloylation of C2 diol was optimized for various acrylating agents and catalysts and led to 80 % yield. The acryloylation of C3 diols was carried out using acryloyl chloride and taking into account the results from C2 optimization (90 % yields). UV curing of C2 and C3 telechelic bis(acrylate)s in the presence of two different photoinitiators (Darocur® 1173 and Irgacure® 819) led to crosslinked films. UV irradiation was performed using two different machines: Fusion UV system Inc., USA and UV-system of Applied Curing Technology Ltd., UK at ETC of DuPont Performance Elastomers, Geneva. It was found that Darocur® 1173 can be successfully used as photo initiator for thin films (less than 0.25 mm) while for thicker films (more than 0.75 mm to 1.5 mm) Irgacure® 819 is more efficient. The gel contents, flexibilities (via the assessment of their glass transition temperatures that ranged between -55 and -30 °C) and thermal behavior (their 10 wt.% losses were ranging between 300 and 350 °C, under air) were investigated. The thermal properties of the resulting materials were better than those of the telechelic poly(VDF-co-PMVE) copolymeric precursors. The UV activated networks of diacrylated fluorooligomers with C3 spacers formed better pale yellow cross-linked films compared to those with C2 spacers.