Preparation And Characterization Of Water Dispersible Core-Shell Polymeric Nano-Particles Based On HEC And PMAA

Polymeric nanoparticles have attracted special attraction due to their great potential applications in biomedicine field. Hydroxyethyl cellulose(HEC) is an important nonionic cellulose derivative which has found very wide applications in industries of latex coating, oilfield treatments, and synthetic materials. However, only a few researches on the preparation of polymeric nanoparticles using HEC as the component were reported.In addition, there are many routes to fabricate polymeric nanoparticles by self-assembly. The traditional self-assembly route to prepare nanoparticles is multi-step, difficult and of low efficiency (<5mg/mL). In the thesis, combining self-assembly and free-radical polymerization, we developed an easy method of "in-situ" polymerization to fabricate core-shell nanoparticles at high concentration in water.Specifically, the following work was carried out:(1) When polymerizing MAA on biocompatible HEC template in an aqueous solution, driven by hydrogen bonding interactions, HEC and poly(methacrylic acid) (PMAA) produced "in-situ" self-assembled into pH-responsive HEC/PMAA nanoparticles composed of bio-compatible HEC shells and insoluble complex cores. By introducing crosslinker N,N'-methylene bisacrylamide into the initial reaction solution, core-crosslinked nanoparticles with a more stable structure could be obtained.(2) Dynamic light scattering and fluorescence techniques were used to trace the polymerization process. The hydrogen bonding interaction between HEC and PMAA, which drove the formation of the nanoparticles, was demonstrated by FT-IR and adding carbamide.(3) The influences of various reaction parameters on the preparation of HEC/PMAA nanoparticles, including the temperature, the medium pH values, the molecular weight of HEC, the concentration of reaction solution, the weight ratio of HEC to MAA , and the crosslinking degree, were studied in details. The results showed that the HEC/PMAA nanoparticles of a smaller size could be prepared at high concentration when using HEC with a molecular weight of 90,000 as the template and carrying out the template polymerization under the conditions as follows: reaction solution of 26.6mg/mL and HEC/MAA1:1, crosslinking degree 5%, pH 2.0, reaction temperature 33°C.(4) The stability and stimuli-responses of HEC/PMAA nanoparticles were investigated. The results show that HEC/PMAA nanoparticles are fairly stable. The size of nanoparticles decrease slightly as temperature increases. In addition, with the increase of pH values, the hydrogen bonding interaction between the components and the hydrophobicity of polymeric core become week, and the structure integrity of the nanoparticles is destroyed as pH increases above 4.0.(5) The internal structure of the HEC/PMAA nanoparticles was observed by TEM. The micrographs show that HEC/PMAA nanoparticles are global and the core-shell structure can be seen clearly for core-crosslinked nanoparticles.(6) The capacity of HEC/PMAA nanoparticles loading dye methylene blue at pH2.0 was determined by spectrophotometry.