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BloconJugate Chem. 1993, 4, 42-40
Temperature-Responsive Bioconjugates. 1. Synthesis of Temperature-Responsive Oligomers with Reactive End Groups and Their Coupling to Biomoleculest Yoshiyuki G. Takei, Takashi Aoki, Kohei Sanui, Naoya Ogata, Teruo Okano,*J and Yasuhisa Sakurait Department of Chemistry, Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda, Tokyo 102, Japan, and Institute of Biomedical Engineering, Tokyo Women’s Medical College, 8-1 Kawada-cho, Shinjuku, Tokyo 162, Japan. Received July 27, 1992
Using 3-mercaptopropionic acid (MPA) as a chain-transfer agent, the radical oligomerization of N-isopropylacrylamie (IPAAm) was carried out with varying molar ratios of MPA to IPAAm in DMF. The molecular weight of oligo-IPAAm (OIPAAm) could be controlled by the ratio of MPA to IPAAm. The OIPAAm was confirmed to average one carboxyl end group per chain. All OIPAAms samples were highly water-soluble at lower temperatures and exhibited phase separation near 32 OC. The optical transmittance of the OIPAAms aqueous solutions changed drastically at 32 “C which was independent of OIPAAms molecular weight. In aqueous solutions of OIPAAm having concentrations higher than 1w t ?& and molecular weight of 6100, the oligomers were precipitated and recovered in 85 wt % yield of their original content. Further, OIPAAm was grafted to atelo collagen by activated ester-amine coupling. The OIPAAm-collagen conjugates were able to dissolved in cold water and precipitated at 34 “C. Temperature-responsive OIPAAm-collagen conjugates are expected to maintain native collagen funtionality in the solution state, react at lower temperatures, and be easily removed from the system with small temperature increases.
INTRODUCTION Poly(N-isopropylacrylamide)(PIPAAm) is well-known to change its structure in response to temperature in aqueous solutions (1, 2). Polymer chains of IPAAm hydrate to form expanded structures in water a t lower solution temperatures (
