Synthesis of surfactant-free hydroxypropylcellulose nanogel and its dual-responsive properties.

Surfactant-free hydroxypropylcellulose (HPC) nanogels were synthesized by using thermo-sensitive HPC as a template to form HPC/PMAA nanoscale complex. The formation mechanism was owing to the interpolymer hydrogen bonding between HPC and PMAA induced phase transition of HPC in aqueous media. The average size of the resulting HPC nanogels ranges from about 98 to 241 nm. It was found that the average size of HPC nanogels changed little with increasing polymerization temperature below 26 °C, whereas it greatly increased above 26 °C. When the concentration of HPC was increased from 0.1 to 0.9 wt.%, the diameter of nanogels decreased firstly and then increased. Besides, an increasing crosslinker BIS concentration led to a reduced size of HPC nanogels, and the nanogels had the narrowest size distribution when its concentration was 0.1 wt.%. In addition to intrinsic thermo-sensitivity, HPC nanogels also display pH-induced phase transition due to pH-responsive PMAA contained in HPC nanogels. Surfactant-free, dual-responsive HPC nanogels would have promising applications in biotechnology and nanomedicine.