New isomers of poly(vinyl fluoride) with controlled regiosequence microstructure

The addition polymer of vinyl fluoride, PVF, contains head-to-head and tail-to-tail structural irregularities (regiosequence defects) caused by monomer reversals during chain propagation. Previously no method existed for significantly altering the level of regiosequence defects, which typically amounts to 10% reverse addition and changes little with polymerization temperature. We report here a novel synthetic procedure which enables us to adjust this defect level by reductive dechlorination of precursor copolymers of vinyl fluoride, VF, with suitable chlorofluoroethylenes, using tributyltin hydride to replace chlorine quantitatively with hydrogen. The products are regioisomers of PVF with defect levels depending on the identity of the chlorofluoroethylene monomer, and the composition of the precursor copolymer, which is selected by adjusting the comonomer feed ratio. Reduction of VF copolymers with vinylidene chlorofluoride yields PVF with defect levels in the range 0–10%, whereas reduction of VF copolymers with 1-chloro-2-fluoroethylene yields PVF with 10–30% defects. We measure the regiosequence distribution of these various PVF isomers by 470 MHz 19F nuclear magnetic resonance, and show that the polymers are stereoirregular (atactic) as well. The crystalline melting temperature of PVF increases as the polymer becomes more isoregic.