Grafting thermoresponsive polymers onto honeycomb structured porous films using the RAFT process

Honeycomb structured porous polymer films were grafted with a thermo-responsive polymer poly(N-isopropylacrylamide) (PNIPAAm) using reversible addition fragmentation chain transfer polymerization (RAFT) under gamma-irradiation in the presence of an additional RAFT agent (S,S-bis(alpha,alpha'-dimethyl-alpha-acetic acid)trithiocarbonate) in solution. The honeycomb structured porous films were successfully prepared from different RAFT group containing polymers (a polystyrene comb and a random copolymer composed of styrene and 2-hydroxyethylmethacrylate PS-ran-PHEMA synthesized in the presence of trithiocarbonates) and from PS-ran-PHEMA obtained via free radical polymerization as a control experiment. Atomic force microscopy (AFM), confocal fluorescent microscopy and contact angle measurements confirm the presence of PNIPAAm chains on RAFT containing polymers while grafted chains were absent in films without any thiocarbonylthio functionality. Microscopy studies (AFM and confocal fluorescent) reveal the presence of PNIPAAm chains primarily inside the pores, clogging the pores in the hydrated state. AFM studies in conjunction with wettability studies confirm the influence of the NIPAAm/RAFT agent ratio in solution with the contact angle decreasing with increasing molecular weight of the attached PNIPAAm chain. The PNIPAAm grafted films were employed to study the cell attachment of fibroblast cells showing that increasing hydrophilicity is beneficial for honeycomb structured porous films to enhance the interaction between the surface and the cells.