Preparation Of Nucleobase-containing Polymers By RAFT Polymerization And Their Molecular Recognition And Self-assembly Behavior

In the early 1950s,Watson and Crick proposed a double helix structure model of DNA.The two nucleotide chains intertwined by complementary base-pairing and maintained structural stability by specific recognition between adenine A and thymine T,guanine G and cytosine C.Scientists' interest in molecular recognition and macromolecule design has stimulated their exploration in many fields.Nucleobase-containing polymer derivatives have great research value in the construction of supramolecular structures,gene therapy and template polymerization.Reversible addition-fragmentation chain transfer(RAFT)polymerization is one of the effective methods to construct nucleobase-containing polymers.RAFT polymerization is based on traditional free radical polymerization system.Chain transfer agent with high chain transfer coefficient is added to react with free radicals to form a dormant radical,so as to realize active controllable polymerization.The advantages of RAFT polymerization are controllable molecular weight,wide application range of monomers,strong molecular design ability,mild and simple reaction conditions.In this dissertation,the end-nucleobase or side chain-nucleobase polymers were obtained by RAFT polymerization,and the polymers which contained different nucleobase were binded with each other.The effects of single disordered or multiple ordered hydrogen bonds on the base-pairing polymers and on the self-assembly behavior were studied.The main research contents are as follows:1.Amphiphilic block copolymers with the addition of end functional group adenine(A)or thymine(T)were synthesized by RAFT polymerization.Nucleobase-containing amphiphilic block copolymers were self-assembled in phosphate buffer saline to form uniformly distributed typical spherical micelles.The nucleobase which exposed to the outer layer of the micelle could interact with the corresponding free nucleobase in the aqueous solution by hydrogen bonding.However,no hydrogen bonding was observed in the structure of the end functional nucleobase which encapsulated in the micelle.High temperature can destroy the hydrogen bonding between micelles and free nucleobase,then release nucleobase from the micelle.2.Four kinds of nucleobase-containing styrene or methacrylate monomers were synthesized.PSA,PST,PSG with rigid styrene as main chain and PmC with flexible methacrylate as main chain were prepared by RAFT polymerization.Base-pairing among different types of nucleobase-containing polymers was investigated.The special hydrogen bonding between nucleobase occurred not only in PSA and PST with the same skeletons,but also in PSG and PmC with different skeletons.Fluorescence quenching rate constants between different types of nucleobase-containing polymers were determined by fluorescence spectroscopy.Static quenching occurred in the systems of PSA and PST,PSG and PmC.Complexe was formed by the hydrogen bonding between the nucleobase.The binding constants of PSA and PST,PSG and PmC were calculated.Nucleobase-containing amphiphilic block copolymers were synthesized by using the obtained polymers as macromolecular RAFT agents.Amphiphilic polymer PSA-b-PNIPAM bind PST-b-PNIPAM and PSG-b-PNIPAM bind PmC-b-PNIPAM complexes were successfully self-assembled in water.Multiple ordered hydrogen bonds could lead to strong and specific interactions and induce spindle-like or telophase-like micelles.3.The nucleobase-containing polymers PSA and PSC with controllable molecular weight and narrow molecular weight dispersity were synthesized by RAFT polymerization.The active group at the end of the polymer was removed by reacting with nucleophilic reagent,and the end-removing products PSAH and PSCH were obtained as mother chains of templated polymerization.MST was added to the PSAH and PSCH systems respectively,and the polymerization was initiated by traditional free radical method.In the system which using PSAH as template,because of the hydrogen bonding between A and T,the monomer MST was guided to find the corresponding position on the mother chain,and the molecular weight and narrow dispersity of the mother chain PSAH were copied into the daughter chain PST.No base-pairing between C and T in PSCH-PST system,so there was no control effect on templated polymerization.Two kinds of polymers with wide molecular weight dispersity were observed in PSCH-PST system.