Over the past 18 years we have been deeply involved with the synthesis and applications of stimuli-responsive polymer systems, especially polymer-biomolecule conjugates. This article summarizes our work with one of these conjugate systems, specifically polymer-protein conjugates. We include conjugates prepared by random polymer conjugation to lysine amino groups, and also those prepared by site-specific conjugation of the polymer to specific amino acid sites that are genetically engineered into the known amino acid sequence of the protein. We describe the preparation and properties of thermally sensitive random conjugates to enzymes and several affinity recognition proteins. We have also prepared site-specific conjugates to streptavidin with temperature-sensitive polymers, pH-sensitive polymers, and light-sensitive polymers. The preparation of these conjugates and their many fascinating applications are reviewed in this article.

A copolymer capable of reaction with biologically active proteins was synthesized by a free radical polymerization in tetrahydrofuran (THF) under anhydrous conditions using azobisisobutyronitrile as the thermal initiator. Longer chain polymers were prepared using benzene instead of THF to avoid chain transfer. The thermally reversible phase transition properties of the copolymers suggested potential applications to the technologies of product isolation and pollutant removal. Conjugation of a monoclonal immunoglobulin to the copolymer is described and utilized in a novel antigen capture fluorescence immunoassay for human IgG.Poly(N-isopropylacrylamide) (polyNIPAAM), formed by a free radical polymerization of N-isopropylacrylamide, is a water soluble, temperature sensitive polymer. In aqueous solution, it exhibits a lower critical solution temperature (LCST) in the range of 30-35°C depending on the concentration and the chain length of the polymer. Thus, as the solution temperature is raised above the LCST, the polymer undergoes a reversible phase transition characterized by the separation of a solid phase which redissolves when the solution temperature is lowered below the LCST. Its physicochemical properties have been investigated by several laboratories (1-3).This thermally reversible precipitation suggested potential applications to the technology of reaction product isolation. It could be used as a tool to allow isolation of a specific product from a totally soluble reaction by raising the temperature.The first step in the process was to covalently incorporate biologically active protein molecules into this polymer. Methods analogous to previous reports (fr-6) involved first adding a functional group to the protein that would provide it with the ability to polymerize, such as a vinyl or substituted vinyl group, followed by copolymerization with the N-isopropylacrylamide monomer in aqueous solution using Ν,Ν,Ν',Ν'-tetramethylethylenediamine and