writer：Qingqing Bian, Yan Xiao* and Meidong Lang*
keywords：ring-opening polymerization (ROP); reversible addition-fragmentation chain transfer (RAFT); controlled/“living” radical polymerization; star polymer
source：期刊
Issue time：2012年
Reversible addition-fragmentation chain transfer (RAFT) polymerization is a more robust and versatile approach than other living free radical polymerization methods for synthesis of well-defined homo-, gradient, block, star-shaped and more complex structural polymers, like micro(nano)gels and polymer brushes. Thus the resultant polymers with thiocarbonylthio-terminated groups are readily tailored to incorporate the functionalized groups. A series of well-defined star diblock [Poly(ε-caprolactone)-b-poly(N-isopropylacrylamide)]4 (SPCLNIP) copolymers were synthesized by RAFT polymerization of N-isopropylacrylamide (NIPAAm) using [Poly(ε-caprolactone)-DDAT]4 (SPCL-DDAT) as macro-RAFT agents (DDAT: S-1-dodecyl-S′-(α, α′-dimethyl-α″-acetic acid) trithiocarbonate). The R-RAFT polymerization showed a controlled/living character, proceeding with pseudo-first-order kinetic behavior. 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 macro-RAFT agents 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 the minimum by careful control of polymerization conditions. Several characterization methods, such as Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR), Gel permeation chromatography (GPC) and Ultraviolet-visible spectroscopy (UV-vis), were applied to confirm the structure and composition of star polymers. Moreover, thermodynamic and crystalline behaviors of the corresponding materials were tested by thermalgravimetric analyzer (TGA) and Differential scanning calorimetry (DSC) and X-ray diffraction (XRD).