Micellization and gelation of the double thermoresponsive ABC-type triblock copolymer synthesized by RAFT

A double thermoresponsive ABC-type triblock copolymer (poly(ethyleneglycol)-block-poly(2-(2-methoxyethoxy) ethyl methacrylate)-block-poly(2-(2-methoxy ethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate, PEG-b-PMEO(2)MA-b-P(MEO(2)MA-co-OEGMA)) was designed and synthesized by reversible additionfragmentation chain transfer polymerization (RAFT). The ABC-type triblock copolymer endowed a thermal-induced two-step phase transition at 29 and 39 A degrees C, corresponding to the thermosensitive properties of PMEO(2)MA and P(MEO(2)MA-co-OEGMA) segments, respectively. The two-step self-assembly of copolymer solutions was studied by UV transmittance measurement, dynamic light scattering (DLS), transmission electron microscopy (TEM) and so on. The triblock copolymers showed the distinct thermosensitive behavior with respect to transition temperatures, aggregate type and size, which was correlated to the degree of polymerization of thermosensitive blocks and the molar fraction of OEGMA in the P(MEO(2)MA-co-OEGMA) segments. In addition, micelles could further aggregate to form the hydrogel by the self-associate of PEG chains under the abduction of the concentration and temperature. The transition from sol to gel was investigated by a test tube inverting method and dynamic rheological measurement.