Temperature triggered antifouling properties of poly(vinylidene fluoride) graft copolymers with tunable hydrophilicity

Abstract

A water soluble polymer poly(diethylene glycol methyl ether methacrylate) (PMeO₂MA) is grafted on a poly(vinylidene fluoride) (PVDF) backbone via coupled atom transfer radical coupling (ATRC) followed by atom transfer radical polymerization (ATRP). The PVDF-g-PMeO₂MA copolymers are designated as PD-24, PD-16, etc. depending on the polymerization time and are characterized using ¹H NMR spectroscopy, FTIR spectroscopy and gel permeation chromatography. AFM images indicate a change in morphology from spherulitic PVDF to the self-organized nano-sphere morphology with hairy PMeO₂MA chains at the surface corona. The TGA data of PD graft copolymers indicate a two-stage degradation whose temperatures are higher compared to those of the components. The glass transition temperatures of the PD graft copolymers are higher than that of PMeO₂MA, and both melting point & crystallinity decrease progressively with an increase of graft conversion. Dynamic light scattering (DLS) data indicate that PD graft copolymers possess a lower critical solution temperature (LCST) at ∼30 °C which can be tuned by changing the composition of the graft copolymer. The antifouling properties of the PD-24 film, produced specifically by water treatment at 15 °C (PD-24-15) and 37 °C (PD-24-37), are tested with bovine serum albumin (BSA) at below and above the LCST and a lower protein adsorption is noticed at 37 °C indicating a temperature triggered antifouling property of the PD graft co-polymers. The surface hydrophilicity of the graft copolymer, measured from the contact angle measurement, is higher in the PD graft co-polymer than that of PVDF and the contact angle decreases more significantly for the PD-24-15 film than that for the PD-24-37 film with time. The filtration of BSA solution using these two films monitored through fluorescence intensity indicates ∼60% protein absorption during filtration through the PD-24-15 film but PD-24-37 does not exhibit any change of fluorescence intensity, indicating superior antifouling properties.