Construction of comb-like poly(N-isopropylacrylamide) layers on microporous polypropylene membrane by surface-initiated atom transfer radical polymerization

In this paper, we describe a thermo-responsive membrane based on microporous polypropylene membrane (MPPM). Comb-like poly(N-isopropylacrylamide) (PNIPAM) was grafted onto the MPPM surface using surface-initiated atom transfer radical polymerization (ATRP). Hydroxyl groups were firstly introduced onto the membrane surface by the ultraviolet-induced graft polymerization of 2-hydroxyethyl methacrylate. Then ATRP initiators were immobilized through the reaction between the tethered hydroxyl groups and 2-bromoisobutyryl bromide, which initiated the ATRP of NIPAM on the membrane surface. Attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy were used to characterize the chemical composition and surface morphologies of the modified membranes. The thermo-response of the modified membranes was evaluated by water contact angle and water permeation measurements. It is found that both water contact angles and water fluxes have obvious response to the environmental temperature. This type of membrane with controlled PNIPAM graft layer can be applied in many fields including smart separation.