| Hyperbranched polymers are a type of macromolecules with highly branched molecular chains,a three-dimensional spheroidal structure and a large number of easily modified terminated functional groups,which can be widely used in drug delivery,smart materials,bioimaging and other fields.However,the preparation of hyperbranched polymers has some limitations such as low degree of branching,easy gelation,wide distribution and difficult control of operating conditions.Therefore,it is critical to seek a simple and efficient preparation method.Hyperbranched stimuli-responsive polymers show greater advantages over the conventional polymers like the sensitivity and selectivity to environmental changes,due to the unique properties of hyperbranched polymers.As a result,it is necessary to prepare novel hyperbranched stimuli-responsive polymers and expand the application.The two novel types of hyperbranched polymers A(A')+B3 and AB(B')with higher degree of branching,even nearly 100%,were prepared by the click chemistry of maleimides and sydnones(SMDC)due to the unequal activity and bifunctional properties of sydnone,and the gelation was effectively avoided.Due to the rigidity and steric hindrance,these hyperbranched polymers had a large internal cavity.Moreover,many carboxyl and tertiary amine groups was introduced into their structures.Therefore,these polymers were very sensitive to pH.In addition,two kinds of hyperbranched polymers were terminated by a large number of highly active maleimide or sydnone groups,respectively,which could be further modified.A therm sensitive poly(N-isopropylacrylamide)(PNIPAM)was prepared by click chemistry reaction of thiol-ene or SMDC to synthesis miktoarm hyperbranched polymers with temperature and pH dual responsiveness,and then were modified with coumarin compounds by esterification to enrich the photoresponsive properties.In addition,the gold nanoparticles were loaded to prepare miktoarm hyperbranched polymer hybrid materials and the self-assembly behavior of miktoarm hyperbranched polymers was studied.This paper contained three parts,as followed.(1)3-(4-carboxyphenyl)sydnone was used as A(A')monomer,tris(2-maleimidoethyl)amine was used as B3 monomer,A(A')+ B3 type hyperbranched polymers,with a high degree of branching,narrow distribution and maleimides terminated groups,were synthesized in a "one-step feed,one-pot" process by SMDC of sydnone and maleimide.The temperature and pH dual responsive A(A')+ B3 type miktoarm hyperbranched polymers were prepared by introducing a therm sensitive PNIPAM hydrophilic chain through thiol-ene click chemistry.The light and temperature dual responsive A(A')+ B3 type miktoarm hyperbranched polymers were prepared by modifying the terminated groups coumarin compounds.Besides,the effect of hydrophilic chains with different molar ratios and molecular weight on polymer structure and properties were studied.The UV-vis was also used to discuss the response of A(A')+ B3 type miktoarm hyperbranched polymer to temperature,pH and light systematically.(2)3-(4-carboxyphenyl)sydnone and furan N-hydroxyethyl maleimide were used to prepare AB(B')monomer with one end of sydnone and the other end of maleimide,AB(B')type hyperbranched polymers with 100%branching and narrow distribution were synthesized by SMDC and a therm sensitive PNIPAM were introduced by the same way to prepare the temperature and pH dual responsive AB(B')type miktoarm hyperbranched polymers with sulfhydryl terminated groups.Besides,the UV-vis was used to study the response of AB(B')type miktoarm hyperbranched polymers to temperature and light specifically.(3)The A(A')+B3 type and AB(B')type miktoarm hyperbranched polymers are both amphiphilic polymers,their self-assembly behavior were observed and the mechanism were studied.Gold nanoparticles,about 10 nm,were prepared by reduction of chloroauric acid with sodium borohydride.Since the end groups were sulfhydryls,gold nanoparticles were loaded to the AB(B')type miktoarm hyperbranched polymers and the change also was observed. |
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