Synthesis Of Functionalized Thermosensitive Polymers And Their Applications In Surface Modification Of Noparticles And Optical Limiting Materials

Poly(N-isopropyl acrylamide)(PNIPAM)is a thermosensitive polymer that has the unique propertiy of the lowest critical solution temperature(LCST)and has been widely studied and applied.Gold nanoparticles(AuNPs)have good optical limiting property,the SPR of AuNPs absorbing laser energy can realize high efficient and rapid photothermal conversion,which can be used to induce the surrounding thermosensitive polymer conformational change and lead to increase of the light scattering and decrease of light transmittance.Therefore,construction of thermosensitive polymer modified AuNPs nanocomposites can effectively enhance their optical limiting properties.In this thesis,thermosensitive polymers with functional end-group(PNIPAM-SH),thermal-and light-responsive PNIPAM-azobenzene polymer(PNIPAM-Azo)and block thermosensitive polymers(PEG-b-PNPAM-SH)were synthesized and the thiol-terminated thermosensitive polymer were used to modify the surface of AuNPs and their optical limiting properties were investigated.The research results as follows:1.S-1-dodecyl-S'-(?,?'-dimethyl-?"-acetic acid)-trithiocarbonate(DDMAT)was synthesised by phase transfer catalysis,then the thermosensitive polymer PNIPAM-CTA with terminal trithiocarbonate was prepared by reversible addition-fragmentation chain transfer polymerization(RAFT)with DDMAT as a chain transfer agent.The LCST of PNIPAM-CTA was determined by UV-Vis spectra and it was found that the concentration has a great influence on its temperature sensitivity.The hydrophobic alkyl group long-chain of PNIPAM-CTA was reduced to a hydrophilic thiol group(-SH)by aminolysis reaction with reducing agent n-butylamine.The LCST of the reduced polymer PNIPAM-SH was elevated.2.Thermal-and light-responsive polymer PNIPAM-Azo was synthesised through the thiol-ene click reaction of azobenzene compound with terminal double bond and PNIPAM-SH,PNIPAM-Azo has good surface activity in aqueous solution and critical micelle concentration(CMC)of PNIPAM-Azo was 0.01 mg/mL;azobenzene changed from stable trans structure to cis structure after ultraviolet irradiation,the photoresponse time in aqueous solution was much longer than that in DMF solution,probably because PNIPAM-Azo self-assembling in aqueous solution affected the structural transformation;the LCST of PNIPAM-Azo was increased after long-term exposure to ultraviolet light.3.The macromolecular chain transfer agent(PEG-CTA)was prepared via the esterification reaction between polyethylene glycol monomethyl ether(mPEG-OH)and DDMAT with 4-dimethylaminopyridine(DMAP)and dicyclohexylcarbodiimide(DCC)as catalytic system.The block polymers PEG-b-PNIPAM-CTA(A,B,C)with different PEG/NIPAM ratios(0.02,0.01,0.005)were prepared by RAFT polymerization with PEG-CTA.4.The PEG-b-PNIPAM-CTA(A,B,C)were educed to PEG-b-PNIPAM-SH(A,B,C)by ammonia hydrolysis method.Effects of reducing agent and solution polarity on the aminolysis reaction were investigated and the optimal reduction conditions(hydrazine hydrate and tetrahydrofuran)were determined.The PEG-b-PNIPAM-SH(A,B,C)with different PEG/NIPAM ratios had different LCST,the higher the PEG/NIPAM ratio,the higher the LCST.5.The AuNPs with good dispersibility and uniform size were prepared by reducing the chloroauric acid solution with sodium citrate.The Au@PNIPAM nanocomposites were prepared via modifying surface of AuNPs with PNIPAM-SH through gold-sulfur bond(Au-S).The AuNPs modified by PNIPAM-SH have good temperature sensitivity and exhibits superior optical limiting performance compared to pristine AuNPs.6.The nanocomposites Au@PNIPAM-b-PEG(A,B,C)were prepared by modifying the surface of AuNPs with PEG-b-PNIPAM-SH(A,B,C).Optical limiting property of three polymer-modified AuNPs was measured and results showed that the laser energy threshold of the optical limiting effect increases along with increase of PEG/NIPAM ratio.