Design,synthesis And Property Of Biobased UCST-type Thermoresponsive Polymers

With the increasing issues in depletion of fossil energy and damage of ecological environment,new materials derived from natural biomass have attracted more and more attentions.To date,although biobased materials with low cytotoxicity and environment-friendliness have been widely used in the fields of biomedical and agricultural science,their thermoresponsiveness is still less explored.Compared with LCST-type thermoresponsive polymers,water-soluble UCST polymers have some intrinsic advantages like the low storage temperature and the transportation convenience,which are the crucial factors in actual biomedical and agricultural production.Moreover,they were discovered just in recent years and only a few of them were reported so far.Therefore,it is of great importance to design and synthesis biobased UCST-type thermoresponsive polymers for the development of intelligent biomedical and agrochemical materials.In this dissertation,natural glycyrrhetinic acid(GA)and gelatin have been used as basic skeletons,respectively,for the preparation of UCST-type linear polymers and crosslinked nanogels.The thermoresponsive principle,the influence factors,and the synergistic effect of host-guest interaction and photothermal property have been investigated systematically.This combination of biobased monomers and UCST thermosensitivity will provide an effective strategy in exploring new biobased functional materials in the field of biomedicine and agricultural science.The major results are as follows:1.A series of GA-appended linear polymers were synthesized by an incorporation of acrylamide monomer functionalized by GA into the polyacrylamide chains,using reversible addition-fragmentation chain transfer polymerization.These linear polymers exhibited the typical UCST thermoresponsive behavior with a cloud point around human body temperature of 37?,mainly promoted by the synergistic effect of H-bonding of amide groups and the face-to-face hydrophobic stacking of GA unit.Moreover,their UCST can be adjusted to the temperature either below 10? or above 40? by altering the content of GA,polymer concentrations,and the host-guest interactions between GA and cyclodextrins,respectively.Such suitable UCST value and the biocompatible nature of GA and cyclodextrins may endow these polymers with potential applications in biomedical chemistry.2.Gelatin-based UCST-type thermoresponsive crosslinked nanogels were synthesized by using the method of reverse microemulsion.These nanogels can be used as the carrier of plant growth regulators with an encapsulation efficiency of 12.2%.On the above basis,a composite nanogel was further prepared by directly doping nano-biochar into the system,which exhibited the typical UCST and near-infrared light responsive behaviors.It is expected that the release of plant growth regulators of this composite nanogel can be regulated by light and heat,thus effectively improving the utilization efficiency of pesticides.