Lower Critical Solution Temperatures of Aqueous Copolymers of N-Isopropylacrylamide and Other N-Substituted Acrylamides

High polymers of N-isopropyl acrylamide (NIPAAM) exhibit a lower critical solution temperature (LCST) in phosphate buffered saline: above 31°C precipitation occurs, with minimal concentration dependence. Copolymers of NIPAAM with acrylamide (AAM), N-methyl acrylamide (NMAAM) and N-ethyl acrylamide (NEAAM) exhibited LCSTs elevated in proportion to their comonomer content. As expected acrylamide was the most effective at elevating the LCST of the copolymer formed. However, NEAAM was more effective than NMAAM. The reason for this is not clear. In contrast, copolymers of NIPAAM with N-t-butyl acrylamide (NTBAAM) exhibited LCSTs that were lowered as a linear function of the comonomer input ratio. Copolymers with N-n-butyl acrylamide (NNBAAM) displayed similar behavior up to 40% NNBAAM, but then the LCST dropped abruptly fron 17°C to below zero. The use of these copolymers in diagnostics and bioseparations is discussed.