Synthesis and Properties of Proton Exchange Membranes via Single-Step Grafting PSBMA onto PVDF Modified by TMAH

Poly(vinylidene fluoride)-graft-poly(sulfobetaine methacrylate) (PVDF-g-PSBMA) proton exchange membranes were synthesized via single-step grafting sulfobetaine methacrylate (SBMA) onto PVDF. Benzoyl peroxide (BPO) was the initiator, and the PVDF was initially modified by tetramethylammonium hydroxide (TMAH) in the liquid phase. Microstructure morphologies and sulfur distributions in the membrane were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX), respectively. The PVDF formed C=C double bonds following dehydrofluorination by TMAH. SBMA was grafted onto the modified PVDF backbones, forming a homogeneous sulfur distribution in the interior and exterior of the membrane. Proton conductivities and methanol permeabilities of PVDF-g-PSBMA membranes increased with the increasing of the TMAH mass fraction in methanol. When the mass fraction was 20%, the proton conductivity of the membrane was 0.0892 S·cm-1 at 20 , and the methanol permeability was 4.04 × 10-7 cm2·s-1 at ambient temperature, respectively. The membrane exhibited good thermal stability up to 270 , as verified by thermogravimetric analysis (TGA). With this membrane, the peak power density of a direct methanol fuel cell (DMFC) was 17.06 mW·cm-2.