Synthesis And Temperature-Sensitive Behavior Of Star Amphiphilic Diblock Copolymer With Cross-linked Shells

The polymerization of N,N'-dimethylacrylamide (DMAA) and 2-(Dimethylamino) ethyl methacrylate (DMAEMA) under atom transfer radical polymerization (ATRP) condition was studied. The ligand, temperature, initiator and reaction time were varied. Better monomer conversions were obtained when ATRP of DMAA was carried out under the conditions that CuBr/Me₆TREN was used as catalysis at 70°C,. However, the conversions were not high, and they remained constant after reaching a maximum value (30%-40%). Compared to DMAA, ATRP of DMAEMA was easily started and higher monomer conversion (90%) was easily obtained at 90°C with CuBr/PMDETA as catalysis. The GPC results showed ATRP of DMAA and DMAEMA was controlled and living polymerization.Then, star polystyrene was obtained via ATRP when multifunctional initiator was used. Based on the above result, ATRP of DMAEMA was carried out with star polystyrene as initiator to get star amphiphilic diblock copolymers, and their micellization behavior was investigated in the mixed solvents (H₂O/DMF). The sizes of micelle could be found by DLS, AFM and TEM. In the mixed solvents, the micelle composed of PS as core, PDMAEMA as shell was formed, and the particle size was in the range of 100-200 nm; as the contents of sample concentration in the system increased, the size of micelle decreased. When the sample concentration was below 0.05%, the micelle disappeared whereas aggregation of micelle was started with the concentration above 1.0%.Based on the above part, we further synthesized shell cross-linked "knedel" (SCK) micelles. This was achieved by reacting partially quaternized PDMAEMA, which acted as micelle shell, with a bifunctional quaternizing agent at 60°C. And with different contents of cross-linked agent, the change of sizes of micelle was different. Besides, we studied temperature-sensitive behavior of SCK micelle, and the result showed that the sizes of SCK micelle changed about 10nm between 35°C and 40°C, and the values of PDI obtained from DLS did not change.