Nanoporous Structures from PS- b-PMMA- b-P tBA Triblock Copolymer and Selective Modification for Ultrafiltration Membranes

A simple approach to fabricating nanoporous structures and their functionality is demonstrated using a triblock copolymer of polystyrene-b-poly(methyl methacrylate)-b-poly(tert-butyl acrylate) (PS-b-PMMA-b-PtBA), where a continuous-type morphology is set in PS matrix to form the cylinders consisting of the PMMA and minor PtBA blocks. For directional and uniform nanochannels at the interfaces, a perpendicular orientation of cylinders was exploited near two interfaces of air/polymer and polymer/neutral substrate, sandwiching the random orientation of cylinders in the interior of the film. Nondegradative, selective swelling-deswelling process of cylindrical (PMMA-b-PtBA) blocks generates nanopores as an effective route to precisely tune the pore size. Further, a simple hydrolysis of tBA units functionalizes the nanopore surfaces and walls into poly(acrylic acid) layers. We demonstrate the pH-responsive water permeability of nanoporous membranes and their active switching with respect to biomolecules such as bovine serum albumin (BSA), suggesting a feasible functional platform to fabricate a stimuli-responsive ultrafiltration membrane using a tunable multiblock copolymer.