Synthesis and Characterization of Novel Copolymers with Different Topological Structures and TEMPO Radical Distributions

A series of novel linear and hyperbranched copolymers with different topological structures and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical distributions were synthesized, and their paramagnetic property was systematically investigated. Based on the ring-opening polymerization (ROP) mechanism of GTEMPO, glycidol (Gly) or ethylene oxide (EO) monomers, the linear Poly(EO-co-GTEMPO) and hyperbranched Poly(Gly-co-GTEMPO) copolymers were obtained from a bifunctional 2,2-dimethyl-1,3-propanediol initiator and a tetrafunctional pentaerythritol initiator, respectively. Alternatively, from the multifunctional macroinitiator of hyperbranched polyglycerol (HPG), the hyperbranched HPG-g-Poly(Gly-co-GTEMPO) and HPG-g-PGTEMPO copolymers were also targeted. The copolymers were characterized by GPC, DSC, and UV-vis analysis. The paramagnetic property of the copolymers was studied and compared by EPR analysis at different concentrations of copolymers and temperatures. The results displayed that the concentrations of copolymers majorly manipulated the signal intensity of EPR spectra, and the temperature majorly modulated the shape of EPR spectra. Essentially, the TEMPO radical distributions in copolymers played an important role: the higher regional density tended to give the EPR spectra with intense, broad peaks, while the lower one led to the regular, well-pronounced EPR spectra. The difference was rationalized to different intramolecular spin-spin exchange and dipole-dipole interaction modulated by the topological structures and the corresponding TEMPO radical distributions.