The Activity Of The Double Sensitive Water-soluble Star Polymer Based On Click Chemistry Can Be Controlled

Due to the special structure of the star polymer,it differs from the traditional chain polymer in many physical and chemical properties,and has attracted wide interest in theoretical research and industrial applications.Therefore,the study of methods for star polymer synthesis has important theoretical and practical significance.The traditional divergence method and the convergence method have disadvantages such as harsh reaction conditions,by-products,and inability to control the number of arms.The active controlled polymerization and click chemistry have good applicability in the synthesis of star polymers.Therefore,we combine the active controlled polymerization and click chemistry to accurately control the formation of star polymers.The purpose of the preparation and research of dual-sensitive star polymers is to explore a method for accurately and controllably synthesizing star polymers.Based on this method,a series of star block polymers are constructed with temperature and pH sensitive monomers.In addition,the relationship between sensitivity and structure is systematically studied to provide a theoretical basis for subsequent structure-activity relationships and applied research.The main research contents and results of this paper include:1.Using ?-cyclodextrin as the initial core of the star polymer,modification was conducted to obtain the 7-arm,14-arm and 21-arm allyl ethers.The chain polymer CTA-PDMAEMA was synthesized via reversible addition-fragmentation chain transfer polymerization(RAFT)and further thiol-transformed to obtain HS-PDMAEMA.Finally,the multi-arm ?-CD allyl ether was grafted with the chain polymer HS-PDMAEMA by a "thiol-ene" click chemical reaction to obtain a star polymer(Star-PDMAEMA).Analysis of the as-prepared products by nuclear magnetic resonance showed that both ?-CD allyl ether and chain polymer were successfully synthesized.However,in the last step,the "thiol-ene" click chemical reaction process has poor controllability,resulting in a low grafting rate of the star polymer,and no accurate target product is obtained.The reason for the analysis is mainly due to the structure of ?-cyclodextrin itself.Its solubility is poor.2.The multi-arm water-soluble star polymer was synthesized by the "Coupling onto" method by means of RAFT combined with "thiol-ene" click chemistry.Firstly,based on pentaerythritol and dipentaerythritol,the terminal hydroxyl groups were modified to introduce a carbon-carbon double bond to obtain 4-arm,8-arm and 12-arm allyl ether,which were further used as the core of the star polymer.A series of chain block polymers CTA-PtBA-b-PDMAEMA and CTA-PDMAEMA-b-PtBA with different molecular weights,block ratios and block sequences were synthesized by step method.Subsequently,thiol was converted by hydrazine hydrate to obtain thiol seal,and the chain block polymers HS-PtBA-b-PDMAEMA and HS-PDMAEMA-b-PtBA were used as the outer arms of the star polymers.The "thiol-ene" click chemical reaction was carried out to graft the thiol-terminated chain block polymer arms with the allyl ether core,generating star polymers Star-PtBA-b-PDMAEMA and Star-PDMAEMA-b-PtBA.Finally,the PtBA blocks in the star polymers were hydrolyzed using trifluoroacetic acid to obtain the final target product water-soluble star polymers Star-PAA-b-PDMAEMA and Star-PDMAEMA-b-PAA.The products of each stage in the above experimental process were characterized by NMR,of which the results was basically consistent with the target product.The molecular weight and distribution of the polymers at each stage were characterized by gel permeation chromatography(GPC).It was found that the molecular weights were basically consistent with the target values,and the molecular weight distributions(PDIs)were relatively narrow.The above analysis shows that the multi-arm star polymers have been synthesized accurately.3.The sensitivity of the as-prepared multi-arm star polymers were investigated using the Zeta potentiometer,dynamic light scattering and ultraviolet-visible spectrophotometer.The influence of the arm number,molecular weight,block ratio and block sequence on the pH/temperature sensitivity of the star polymer solution was studied.It was found that the pH sensitivity of star polymers is directly related to their block sequences.For the star polymer Star-PAA-b-PDMAEMA,when the pH of the solution is acidic,the PAA segment shrinks and nucleates and the PDMAEMA segment stretches into a shell,so the star polymer is hydrophilic as a whole,and the particle size is higher.When the pH of the solution is alkalic,the PAA segment stretches into a shell and PDMAEMA shrinks and nucleates,resulting in the star polymer being hydrophobic overall and having a small particle size.The case of the star polymer Star-PDMAEMA-b-PAA is opposite,in which Star-PDMAEMA-b-PAA has a smaller particle size in an acidic solution than in an alkalic environment.However,the influence factors of the temperature sensitivity of the star polymers are more complicated.Through systematic research,it was found that the number of arms,molecular weight,block ratio and block sequence of star polymers have certain influence on their temperature sensitivity.