This study was carried out to characterize the reactivity of temperaturesensitive, protein-conjugating polymers prepared by a photopolymerization process. Polymers were based on N-isopropylacrylamide (NiPAM) and N-acryloxysuccinimide (NASI). A photoinitiator, 2,2-dimethoxy-2-phenyl-acetophenone, and monomers at desired ratios were polymerized in a glass flask using an UV source. Polymers were characterized for composition, molecular weight (MW), cloud point temperature (CPT), hydrolysis and aminolysis rates (using ethanolamine as a model compound), and protein conjugation. The monomer feed ratio was found to effectively control the composition of the synthesized polymers. The polymer MWs were between 10 and 20 kD, depending on the polymerization solvent. The CPT of NiPAM/NASI polymers did not depend on NASI content (Υ
5.6%), nor did the hydrolysis and aminolysis rates. Compared to NASI monomer, the polymerized NASI exhibited a 6-and 120-fold slower rates of hydrolysis and aminolysis, respectively. Although hydrolysis and aminolysis rates were higher at higher pHs, the relative aminolysis : hydrolysis rate was highest at a pH of 7.4, which also gave the most effective protein conjugation. We conclude that characterizing the polymer reactivity is useful for predicting the optimal conditions for protein conjugation and may facilitate the design of polymers with improved protein conjugation kinetics.