The Synthesis And Characteristics Of UCST Triblock Polymer Based On P(AM-co-AN)

Smart hydrogel is an important polymer material,which has broad prospects in academic research and industrial applications.Especially in a drug delivery system,it can respond to specific physiological triggers to release the embedded drug at the appropriate time and site of action.In recent years,the synthesis,self-assembly,sol-gel behavior,and drug loading-release characteristics of stimulus-responsive hydrogels have become research hotspots in the field of polymer and materials science at home and abroad.In this paper,three brand new multi-stimulus response triblock polymers with temperature-sensitive response based on P(AM-co-AN)were designed and synthesized by the reversible addition-fragmentation chain transfer polymerization(RAFT)method with 2-(2-cyanopropyl)dithiobenzoate(CPDB)as a chain transfer agent.And the environmental response characteristics,biological toxicity and drug-controlled release applications of these polymers in aqueous solution were systematically studied.The main research contents and results are as follows:(1)The first block PtBA was synthesized from the hydrophobic monomer t-butyl acrylate(tBA)by RAFT polymerization.Then,the hydrophilic block N,N-dimethylacrylamide(DMA),acrylamide(AM)and acrylonitrile(AN)were sequentially introduced to synthesize the temperature-sensitive triblock copolymer PtBA-b-PDMA-b-P(AM-co-AN).After hydrolysis,a temperature/anionic pH-responsive triblock polymer PAA-b-PDMA-b-P(AM-co-AN)(ADAA)was obtained.The molecular structure and molecular weight of the polymer were initially determined by FT-IR,1H NMR and GPC,and the final polymer composition was PAA120-b-PDMA373-b-P(AM150-co-AN50).The self-assembly process of ADAA at low concentration was studied by DLS,turbidimetry and TEM.ADAA self-assembled into different nanostructures including molecular chains,core-shell-corn,core-linking-core and tighter dual-core structures in aqueous solution with changes in temperature and pH.The sol-gel transition behavior of ADAA was studied by viscometer,rheometer and SEM.Above the lowest concentration(～7 wt%),the reversible sol-gel transitions of ADAA could be controlled by adjusting pH and temperature.And the phase transition temperature was regulated by the concentration and pH value.In addition,MTT toxicity experiments have proved that ADAA has good biocompatibility.And when it was injected into a device that simulates the human environment,the result indicated that the addition of the triblock polymer as a drug carrier could effectively reduce the instantaneous drug concentration and prolong the drug release time.(2)First,UCST-type temperature-sensitive material P(AM-co-AN)was synthesized with acrylamide(AM)and acrylonitrile(AN).Then,the UCST-type temperature/cation pH-sensitive triblock polymer P(AM117-co-AN35)-b-PDMA475-b-P4VP74(VDAA)was successfully synthesized by the RAFT polymerization method with the pH-sensitive material 4-vinylpyridine(4VP).At low concentrations,with the change of temperature and pH,VDAA undergone reversible structural transformations of core-shell-corn and core-linking-core.At high concentrations,the gel behavior of VDAA was mainly attributed to the cross-linking of hydrogen bonds inside PAM.After the concentration reached the minimum concentration,once the temperature was lowered or the pH value was raised,VDAA would change from a flowing slab sol state to a honeycomb-like weak gel state with regular holes and then into an independent cross-linked dense fibrous gel.(3)Based on the previous two chapters,we replaced the pH response block with an LCST temperature response block.The dual temperature sensitive polymer P(AM89-co-AN23)-b-PDMA475-b-PNIPAM57(NDAA)was successfully synthesized by RAFT polymerization method.The synthesized NDAA was composed of an LCST type(PNIPAM)and a UCST type temperature-sensitive block(P(AM-co-AN)),and its LCST was higher than UCST.At low concentrations,as the temperature went from low to high,NDAA undergone a reversible structural transformation from core1-shell to full dissolution and then to core2-shell.At high concentrations,the gel behavior of NDAA was mainly due to the hydrogen bond cross-linking between PAM and PNIPAM.After the concentration reached the lowest concentration,NDAA could easily form a dense and regular honeycomb gel state at low temperatures.In short,it is hoped that this research can highlight the superiority of UCST-type thermosensitive polymers in various application fields,and provide an effective reference for the research and application of environmental stimulus-responsive polymers.