(439d) Synthesis of Poly(vinylidene fluoride)-b-Poly(N-vinylpyrrolidone) Block Polymers By Iodine Transfer Polymerization and Their Use As Membrane Additives

Poly(vinylidene fluoride) (PVDF) is one of the most important polymers used in preparing of porous membrane for water treatment. However, the hydrophobic nature of PVDF always causes the fouling and flux decline of membranes. Much effort has been devoted to improve the hydrophilicity of PVDF by blending PVDF with hydrophilic polymers, graft polymerization of hydrophilic monomer on the PVDF backbone by the conventional and controlled/living radical polymerization after pre-treatment of PVDF by a γ irradiation, electron beam irradiation, plasma, UV and so on. And there are few reports about the modification of the hydrophilicity of PVDF by block polymerization. Herein, we report the hydrophilic modification of PVDF by block polymerization of iodine terminated PVDF (PVDF-I) with N-vinylpyrrolidone (NVP), resulting in PVDF-b-PNVP block polymers. Firstly, PVDF-I was synthesized by iodine transfer polymerization of VDF mediated by C₆F₁₃I in an aqueous dispersed system, then the synthesized PVDF-I was dissolved in N,N-dimethylacetamide (DMAc) and used as a transfer agent for the polymerization of NVP. ¹H NMR spectra confirmed that the content of the PNVP block agreed with the NVP conversions. ¹⁹F NMR spectra showed the difference of the chemical environment of the F atoms between PVDF-I and PVDF-b-PNVP copolymer, which confirmed the validity of PVDF-I and structure of PVDF-b-PNVP. The PVDF-I exhibited α crystalline phase, while the PVDF-b-PNVP exhibited α to γ transition crystalline phase. Polar optical microscope images revealed that in the isothermally crystallization process, the spherulitic crystal of the PVDF-I was destroyed by incorporating PNVP block. The crystallinity and crystallization temperature of PVDF-b-PNVP were lower than that of PVDF-I, and decreased with the increase of content of PNVP block. Water contact angle test revealed that PVDF-b-PNVP was more hydrophilic than PVDF-I. Water flux tests revealed that PVDF-b-PNVP could greatly improve the water flux and lifetimes of the PVDF membrane.