Preparation of thermoresponsive cationic copolymer brush surfaces and application of the surface to separation of biomolecules

We have prepared poly(N-isopropylacrylamide (IPAAm)-co-2-(dimethylamino)ethylmethacrylate (DMAEMA)) brush-grafted silica bead surfaces through surface-initiated atom transfer radical polymerization (ATRP) using the CUCl/CUCl₂/Me₆TREN catalytic system in 2-propanol at 25 °C for 16 h. The prepared temperature-responsive surfaces were characterized by chromatographic analysis using the modified silica beads as stationary phases. Chromatographic retention times for adenosine nucleotides in aqueous mobile phases were significantly increased compared to that previously reported for other cationic hydrogel surfaces, indicating that strong electrostatic cationic copolymer brush interactions occur between the surfaces and nucleotide analytes. Retention times for adenosine nucleotides significantly decreased with increasing column temperature, explained by the decreasing basicity in the copolymer with increasing temperature. Step-temperature gradients from 10 to 50 °C shorten ATP retention times. These results indicate that cationic copolymer brush surfaces prepared by ATRP can rapidly alter their electrostatic properties by changing aqueous temperature.