(734b) PSMA-B-PNIPAM Copolymer Micelles with Both a Hydrophobic Segment and a Hydrophilic Terminal Group: Synthesis, Micelle Formation and Characterization

PSMA-b-PNIPAM copolymer micelles with both a hydrophobic segment and a hydrophilic terminal group: Synthesis, micelle formation and characterization

Amphiphilic and thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) copolymer micelles are well known and extensively studied. However, block copolymers of PNIPAM with both a hydrophobic segment and a hydrophilic terminal group in the same chain are relatively rare. Herein, we report a systematic study of two different kinds of PNIPAM copolymers synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization. One is a diblock copolymer with only hydrophobic poly(stearyl methacrylate) (PSMA) chain segments, while the other is a triblock copolymer with both a PSMA segment and a hydrophilic terminal group. Uniform spherical micelles were obtained. NMR and GPC have been applied to characterize the structures and fluorescence measurements has been made to determine the critical micelle concentrations (CMCs). Micelle sizes were measured by dynamic light scattering (DLS) and lower critical solution concentrations were determined by UV/Vis spectrophotometry. TEM was used to characterize the microstructures of the micelles, and their microphase separation behavior was analyzed by small angle X-ray scattering (SAXS).

All the copolymers displayed relatively low CMCs. That is to say, they could form micelle in relatively low concentrations. All CMCs for the diblock copolymers were larger than those for the triblock copolymers, which might be attributed to hydrophilicity. When the samples are more hydrophilic, they can more easily form micelles. The size of the diblock copolymer micelles first decreased and then became stable. However, the triblock copolymer micelles showed a distinct evolution, first becoming small, then becoming larger, and finally becoming stable. The transition process was fast and reversible with temperature. The LCSTs of the diblock copolymers were all lower than that of PNIPAM homopolymer, consistent with previous literature reports. However, the LCSTs of the triblock copolymers were almost as high as that of PNIPAM homopolymer. In the triblock copolymer, hydrophobic chains and hydrophilic segments co-existed, and their opposing effects partially canceled. The hydrophilic terminal group on the triblock copolymer made a great difference. The micelles showed great performances and might find potential applications in wide fields.