Synthesis Of UCST Aliphatic Polycarbonates Based On Thiol-yne Click Reaction

Stimuli-responsive polymers（smart polymers）have attracted much attention due to their properties of changing certain physicochemical properties with internal and external stimuli,including temperature,p H,light,reactive oxygen species,electromagnetic fields,etc.Temperature,being one of the easi est methods to achieve and control,has made temperature-responsive polymers a focus of design and research.Temperature-responsive polymers are mainly classified into LCST（Lower Critical Solution Temperature）and UCST（Upper Critical Solution Temperature）types.There is relatively little research on UCST type polymers,and most of the existing polymers have poor biocompatibility and biodegradability,making them difficult to be used in biomedical applications,such as drug delivery,controlled drug release,and targeted cancer therapy.Aliphatic polycarbonates are widely used because of their excellent low toxicity,biocompatibility and biodegradability,but traditional aliphatic polycarbonates lack functional groups,so they are generally modified by polymerization of functional monomers to give them the required properties.In this thesis,aliphatic polycarbonates with UCST phase behavior were synthesized and their thermal responsiveness was effectively modulated by post-polymerization modification means with alkyne-functionalized aliphatic polycarbonate as the backbone,which was divided into three main parts as follows:（1）Functional aliphatic polycarbonates PMPC_n with alkyne pendent groups in the side chains were synthesized by ring-opening polymerization of alkyne-functionalized six-membered cyclic carbonate monomer MPC.Thiol-yne click reaction between PMPC_n and MPA and/or MSA was conducted to synthesize multi-series of carboxyl modified aliphatic polycarbonates PMPC _n-（MPA_a-MSA_b）with different degrees of polymerization and different click ratios.The UCST performance of the polymers in water,the influence of various factors on the phase separation behavior and their principles were further investigated,which broaden the application of aliphatic polycarbonates,and the thiol-yne click reaction provided a facile method for the rational design of polymers with excellent UCST phase separation behavior.（2）The ring-opening copolymerization of MPC with the non-functionalized monomer DTC was utilized to prepare a partially alkyne-functionalized aliphatic polycarbonate P（DTC_x-co-MPC_y）with different copolymerization ratios,and then the random copolymer was modified with carboxyl groups by thiol-yne click reaction with MSA to synthesize a gradient random copolymer P(DTC_x-co-MPC_y^4-COOH)with different degrees of carboxyl functionalization.The effect of carboxy group density that was determined by the ratio of the two monomers on the phase separation behavior was further investigated,and the results provide an alternative approach for the effective synthesis of aliphatic polycarbonates with UCST phase separation behavior.（3）Using the aliphatic polycarbonate PMPC _n with alkynyl pendent groups in the side chains of different degrees of poly merization as raw materials,hydroxyl-modified aliphatic polycarbonate PMPC_n-（ME_a-MPD_b）were obtained via click reaction with ME and MPD.While changing the degree of polymerization of PMPC_n and the ratio of ME to MPD,tunable and controllable UCST behavior of the obtained polymers in ethanol/water binary mixed solvent were developed.The polymers with UCST phase separation behavior in a low toxic mixed solvent of ethanol/water have great potential in sensors,drug carriers or pharmaceutical applications.