A series of biodegradable thermosensitive copolymers was synthesized by free radical polymerization with N-isopropylacrylamide (NIPAAm), acrylic acid (AAc) and macromer 2-hydroxylethyl methacrylate-poly(ε-caprolactone) (HEMAPCL). The structure and composition of the obtained terpolymers were confirmed by proton nuclear magnetic resonance spectroscopy, while their molecular weight was measured using gel permeation chromatography. The copolymers were dissolved in phosphate-buffered saline (PBS) solution (pH = 7.4) with different concentrations to prepare hydrogels. The lower critical solution temperature (LCST), cloud point, and rheological property of the hydrogels were determined by differential scanning calorimetry, ultraviolet-visible spectrometry, and rotational rheometry, respectively. It was found that LCST of the hydrogel increased significantly with the increasing NIPAAm content, and hydrogel with higher AAc/HEMAPCL ratio exhibited better storage modulus, water content, and injectability. The hydrogels were formed by maintaining the copolymer solution at 37°C. The degradation experiment on the formed hydrogels was conducted in PBS solution for 2 weeks and demonstrated a less than 20% weight loss. Scanning electron microscopy was also used to study the morphology of the hydrogel. The copolymer with NIPAAm/AAc/HEMAPCL ratio of 88:9.6:2.4 was bioconjugated with type I collagen for the purpose of biocompatibility enhancement. In-vitro cytotoxicity of the hydrogels both with and without collagen was also addressed.

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Reversible addition-fragmentation chain transfer (RAFT) polymerization is a more robust and versatile approach than other living free radical polymerization methods, providing a reactive thiocarbonylthio end group. A series of well-defined star diblock [poly(e-caprolactone)-b-poly(N-isopropylacrylamide)] 4 (SPCLNIP) copolymers were synthesized by R-RAFT polymerization of N-isopropylacrylamide (NIPAAm) using [PCL-DDAT] 4 (SPCL-DDAT) as a star macro-RAFT agent (DDAT: S-1-dodecyl-S 0 -(a, a 0 -dimethyl-a 00 -acetic acid) trithiocarbonate). The R-RAFT polymerization showed a controlled/''living'' character, proceeding with pseudo-first-order kinetics. All these star polymers with different molecular weights exhibited narrow molecular weight distributions of less than 1.2. The effect of polymerization temperature and molecular weight of the star macro-RAFT agent on the polymerization kinetics of NIPAAm monomers was also addressed. Hardly any radical-radical coupling by-products were detected, while linear side products were kept to a minimum by careful control over polymerization conditions. The trithiocarbonate groups were transferred to polymer chain ends by R-RAFT polymerization, providing potential possibility of further modification by thiocarbonylthio chemistry. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 571-580, 2012

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