Preparation And Surface Properties Of Poly(N-isopropylacrylamide)-Grafted Polypropylene Membranes

As a thermoresponsive polymer,poly(N-isopropylacrylamide)(PNIPAAm)has received increasing attention.By combining the thermoresponsive property of PNIPAAm with the excellent mechanical property of porous substrates,PNIPAAm-grafled membranes have potential applications in biotechnology and intelligent separation systems.In this work,graft polymerization of NIPAAm onto microporous polypropylene(PP)membranes was carded out by UV-induced graft polymerization and surface-initiated atom transfer radical polymerization(ATRP).Surface properties of the modified membranes were studied in detail.PNIPAAm was grafted onto PP membranes by UV-induced graft polymerization. Effects of preparation conditions,such as monomer concentration,UV-irradiation time and photoinitiator concentration on the grafting degree were studied.Chemical and morphological changes of the membrane surface were confirmed by attenuated total reflectance Fourier transform infrared spectroscopy(FT-IR/ATR),X-ray photoelectron spectroscopy(XPS)and field emission scanning electron microscopy(FESEM). Membranes dried at 25℃and 60℃exhibited different morphologies because of the thermosensitive behaviors of PNIPAAm layer.The time-dependence of water contact angle and the advancing/receding contact angle were measured by sessile drop and dynamic Wilhelmy plate technique.Results indicated that the water contact angles were temperature-dependant.Surface-initiated ATRP was further employed to construct controllable PNIPAAm-grafted PP membranes.2-Hydroxylmethyl methacrylate was first grafted to the PP membrane surface by UV-induced graft polymerization.Reaction between the hydroxyl groups and 2-bromopropionyl bromide gave the immobilization of ATRP initiator. Surface-initiated ATRP of NIPAAm was then carded out.The chemical and morphological changes of the modified membrane surfaces were characterized by FT-IR/ATR,XPS and FESEM.The contact angle decreased with temperature,and remarkable changes were observed between 30℃and 35℃.