POLYSTYRENE SURFACE GRAFTED WITH POLY(N-ISOPROPYLACRYLAMIDE) BRUSHES

Abstract

Porous polystyrene (PS) film was prepared by casting a mixed solution of polystyrene (Mw=3x106 Daltons) and block copolymer of polystyrene and poly(acrylic acid) (PS130-b-PAA12) in weight ratio of 9:1 on glass substrate via breath figure method. As monitored by scanning electron microscopy, the casted film was porous and exhibited ordered honeycomb pattern with pore diameter of 7.67±0.69 µm. This porous PS film was then coated with polydopamine modified with bromoester group (p-DA-BiBBr) that functions as initiator for growing thermoresponsive poly(N-isopropylacrylamide) brushes via activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP). The success of p-DA-BiBBr coating and PNIPAM grafting on porous PS film was verified by water contact angle measurements, Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and x-ray photoelectron spectroscopy (XPS). As evaluated by proton nuclear magnetic resonance (1H NMR) spectroscopy and gel permeation chromatography (GPC), the synthesized PNIPAM in solution had a degree of polymerization around 300. The thickness of the PNIPAM layer was found to be 18.3 nm as estimated by ellipsometry. This thickness should be suitable for cell attachment and detachment studies. From preliminary investigation, it was found that approximately 12% of attached keratinocyte cells at 37oC were detached from PNIPAM-grafted porous PS film when the temperature was decreased to 20oC, below LCST of PNIPAM, for 2 h. However, such percentage of cell detachment was not significantly different from that of PNIPAM-grafted flat PS film (10%).