The Synthesis And Performance Study For The Thermosensitive PNIPAM-AuNPs And PNIPAM-DNA

Poly(N-isopropylacrylamide)(PNIPAM)is one of the thermally responsive polymers,which has a lower critical solution temperature(LCST),and there is a phemomenon of the conformation variation around this temperature.Below the LCST,PNIPAM can exist in the water stability by the hydrogen between the hydrated group and water,the polyer chain adopts an extended coil conformation and PNIPAM is hydrated,while above the LCST,the hydrogen is broken,the polymer is dehydrated and daopts a globular conformation aggregates.The modification of PNIPAM play an important role in so many areas,such as the drug delibery、gene transfer and biochemical analysis and so on.In this paper,the PNIPAM-AuNPs composite was synthesized according to the principles of reversible addition-fragmentation chain transfer(RAFT)polymerization and the ammonolysis of ethanolamine,and then studied the salt effection by many different ions;at the same time,the PNIPAM-DNA block copolymer was synthesized according the principles of activator generated by electron transfer for ATRP(AGET ATRP)polymerization and the mechanism of click reaction,which was used to studied the chang of LCST caused by the DNA conformation variation.1.The systhesis of PNIPAM-COOH via RAFT polymerization using 4-cyanopentanoic acid dithiobenzoate(CPADB)as RAFT agent,azobis-(isobutylronitrile)as the initiator and N,N-dimethylformamide(DMF)as solvents,the resulting PNIPAM had controlled molecular weights and the PDI was low.The systhesis of PNIPAM-Br via AGET ATRP polymerization using ethyl bromoisobutyrate(EBIB)/CuBr2 /N,N,N’,N,’’N’’-Pentamethyldiethylenetriamine(PMDETA)as an initiator/catalyst system,sodium ascorbate as the reduction,and the characterization results show that they have clear structure.2.The dithioester end group can be reduced to a thiol by the ammonolysis of ethanolamine,and PNIPAM-AuNPs composite was prepared via reactions of the tterminal thiol with gold.It can exist stability in aqueous solution,and different ions has different salt effect for the composite.Below the LCST,the comprehensive affection of the charge and the complexation which result in Hg2+ >Cu2+ > Zn2+> Ni2+> Pb2+ > Na+;above the LCST,the compesite get to aggregate owing to the salt and heat effect,and the result is Cu2+ > Pb2+ > Zn2+> Ni2+> Hg2+ > Na+,the complexation becomes weak while the salt effect still cannot to be neglected,so the effect of Cu2+ and Pb2+ is similar,Ni2+ and Hg2+ is similar,the effect of Na+ is still lowest.3.The PNIPAM-DNA block copolymer is systhesised by the click reaction between the acetylene modified DNA and the azide modified PNIPAM which was prepared from PNIPAM-Br via sodium azide.Under different temperature,we detect the transmittance of PNIPAM-DNAC in acid and alkaline solution and PNIPAM-DNAT in the solution with and without mercury to study the change of LCST caused by the DNA conformation variation.The single-stranded DNAC can switch to tetrahedron structures in acid solution(pH<6.0)and the DNAT become into duplex structures via the formation of a Hg2+-mediated base pair,T-Hg2+-T,and as a result,these DNA conformation variation make the DNA have more negative charges,and then strengthen the electrostatic repulsion between DNA chain,all of them have a resultion that the phase transition of PNIPAM-DNA becomes wider and slow,the hydrodynamic is reduced and the transmittance of the solution is improved.