Degradable Polymers With LCST/UCST:Synthesis,Characterization And Temperature Sensitivity

Smart-responsive polymers is a hot topic of current research that can respond to single or multiple stimuli such as pH,magnetic fields,electric fields,stress,temperature,light,biomolecules,and more.While temperature is one of the most interesting properties of smart-responsive polymers.The reasons for the most extensive research on temperature-sensitive polymers are not only the variety of the available temperaturesensitive materials but also temperature is the safest,most controllable and achievable external stimulus.Temperature-sensitive polymers are mainly divided into two categories,one with the lowest critical solution temperature(LSCT)and the other with the highest critical solution temperature(UCST).However,most temperature-sensitive polymers have limited application in production and life due to their non-degradability.Therefore,the synthesis of degradable,temperature-sensitive polymers with good biocompatibility is currently a major trend.This paper used the norbornene-functionalized polylactide(PLA)as the carrier,and the 1,3-dipolar cycloaddition reaction was first carried out to graft polyethylene glycol monomethyl ether(MPEG)on the side chain,and 1-thioglycerol undergoes a "mercapto-ene" click reaction,then by activation of the hydroxyl group with pnitrophenyl chloroformate(NPC),and finally amidation with isopropylamine to give the final temperature-sensitive polymer(P(LA-g-MPEG)/IPA).The synthesis of the aqueous polymer in our study has a typical LCST phenomenon: the aqueous solution is clear and transparent at low temperatures,When the temperature is higher than the critical solution temperature,that is,the phase transition temperature(Cp),it is a milky white turbid liquid.Moreover,the phase transition temperature and the concentration of the aqueous polymer solution are dull,and are closely related to the molecular weight of polyethylene glycol monomethyl ether,the degree of polymerization,the ratio of polyethylene glycol monomethyl ether and isopropylamide.Increasing the molecular weight of polyethylene glycol monomethyl ether to increase its critical solution temperature,increasing the degree of polymerization and increasing the proportion of isopropylamide groups all lower the phase transition temperature.In addition,the norbornene-functionalized polylactide was also used as a carrier in this paper to carry out the "mercapto-ene" reaction directly with mercapto succinic acid,and then DIC condensation reaction with sulfated 8-hydroxyquinoline to obtain ionic liquid polymer P(LA-g-HQS).This polymer has a typical UCST phenomenon in PBS buffer solution: the polymer solution is milky and turbid at low temperature,and when the phase transition temperature is higher than that,the solution is clear and transparent.And its phase transition temperature is closely related to the concentration of the polymer solution and the degree of polymerization.With the increase of the concentration of the polymerization solution and the degree of polymerization,the phase transition temperature becomes higher.