Cylindrical Pores Responding to Two Different Stimuli via Surface-Initiated Atom Transfer Radical Polymerization for Synthesis of Grafted Diblock Copolymers

Functional polymeric materials with cylindrical pores where effective pore size can be significantly and reversibly manipulated by combination of two different stimuli, here combinations of pH and temperature.. have been successfully prepared by surface-selective ATRP from the pore surface of track-etched poly(ethylene terephthalate) membranes with pore diameters of 790 and 1900 nm. Initiator immobilization on the poly(ethylene terephthalate) surface in a density of similar to 1 group per nm(2) was done via already reported solid phase chemistry. An ATRP system with copper(I) chloride/tris(2-(dimethylamino)ethyl)amine as catalyst and N,N-dimethylformamid as solvent was established what allows the controlled grafting of poly(N-isopropyl acrylamide) and poly(tertbutyl acrylate) and of their diblock copolymers in both different sequences. Conditions for hydrolysis of grafted poly(tert-butyl acrylate) to poly(acrylic acid) in the poly(ethylene terephthalate) pores without changing the substrate structure had also been established. The well-defined porous polymer substrate allowed to obtain qualitative and quantitative information on the functional layers in dry state (from gravimetry, IR spectroscopy and liquid dewetting permporometry), and-via analysis of membrane permeability-on effective thickness, density and reversible swelling ratio of these grafted layers in wet state. It is remarkable that dry poly(N-isopropyl acrylamide) layer thicknesses of several hundred nanometers Could be obtained in only 4 h reaction time. All data indicate that crafted poly(N-isopropyl acrylamide) and poly(acrylic acid) with a "brush" structure have been achieved: however. the poly(N-isopropyl acrylamide) brush layers had a higher density what could be related to the lower reactivity of the functional monomer. The effective layer thickness of the grafted diblock copolymer layers could be reversibly changed in four steps by up to 200 nm via different combinations of pH (between 2 and 7) and temperature (23 and 45 degrees C).