Construction Of Temperature And Ph Stimuli-responsive Polymers Based On Nucleobase Complementary Pairing

DNA is joined together by complementary nucleobases containing specific hydrogen bonds to obtain a complex double helix structure.The specific recognition characteristic of bases has attracted the attentions of many researchers.Recognizing the enormous potential of bases,researchers have developed base-pairing interactions into other areas,such as drug release,template polymerization,and so on.Reversible addition-fragmentation chain transfer(RAFT)polymerization method is often applied to the preparation of block polymers and has good control over the polymerization process of base-containing monomers.In this paper,base-containing monomers and a base-containing RAFT reagent were synthesized,and double-end base functionalized polymers and side chain base polymers were prepared by RAFT polymerization.The effect of rigid hydrophobic segments on rigid amphiphilic block polymer assemblies was first investigated.The effects of various factors on the micro-gels produced by the rigid hydrophobic segments and the flexible hydrophilic segments were then investigated.The main research contents are as follows:1.Self-assembly of base-containing rigid polymersThe amphiphilic block copolymer PsA22-b-PNIPAM85 was prepared by RAFT polymerization,one being a rigid hydrophobic polymer PsA containing adenine and the other being a hydrophilic polymer PNIPAM having LCST.In addition,an additional thymine-containing rigid hydrophobic polymer PsT25 was prepared.First,an amphiphilic block copolymer PsA22-b-PNIPAMg5 assembly was obtained.The effect of the rigid hydrophobic polymer PsT25 on the assembly of the amphiphilic block polymer PsA22-b-PNIPAM85 was investigated due to the hydrogen bonding between adenine and thymine.PsT25 will have an impact on the assembly of PsA22-b-PNIPAM85.Compared with the PsA22-b-PNIPAM85 assembly system,the addition of PsT25 makes the temperature response of the system difficult to observe.Since the acidic solution destroys the hydrogen bonding between thymine and adenine,the addition of PsT25 gives the system an acidic response.2.Preparation of micro-gels based on three-dimensional network interpenetrating structureThymine is introduced into the RAFT reagent by an esterification reaction,and then subjected to RAFT polymerization to obtain T-PNIPAM-T having a flexible segment which is hydrophilic.At the same time,PsA having a rigid segment which is hydrophobicity was obtained by RAFT polymerization.The two polymers are hydrophilic and one is hydrophobic;one is flexible and the other is rigid.The rigid polymer is restricted in motion,and the flexible polymer is easier to move,so the rigid polymer and the flexible polymer will undergo network interpenetration.So micro-gels can be formed into a three-dimensional network interpenetrating structure.The effects of temperature,water content in DMSO/H2O solution,hydrophilic segment T-PNIPAM-T with different polymerization degrees,pH value of the aqueous solution on the morphology and particle size of the micro-gels were investigated.(1)With the increase of temperature,the transmittance of the micro-gels composed of PsA20/T-PNIPAM80-T increased,and the particle size of DLS measured also increased.(2)The increase of water content did not affect the morphology of the micro-gels composed of PsA20/T-PNIPAM80-T,but its particle size decreased with the increase of water content,and the increase of water content made the structure of the macro-gels more compact.(3)The degree of polymerization of the hydrophilic segment T-PNIPAM-T affected the LCST of the obtained micro-gels and had a regulatory effect on the LCST of the system.(4)The hydrogen bonding between adenine and thymine made the PsA20/T-PNIPAM80-T micro-gels have an acidic response.