CO₂ Reversible Iminophenyl Borate Link Type LCST Hyperbranched Polymer

Under external stimuli,such as pH,CO2,temperature,ionic strength and redox,the structure and properties of stimuli-responsive polymers(SRPs)will change significantly.Therefore,SRPs can be used as advanced functional materials in many fields.Among these SRPs,polymers with low critical solution temperatures(LCST)are the most widely studied.In addition,CO2-responsive polymers have many applications in gas-switchable materials due to the the stimulation strength of CO2 can be easily tunable without salt accumulation and inexpensive,etc.Therefore,CO2-responsive polymers have attracted more and more attention in the recent years.On the other side,hyperbranched polymers have a series of excellent physical and chemical properties,such as a large number of terminal functional groups,low viscosity,high rheological properties,good solubility and three-dimensional branched structures,etc.These unique properties cannot be reached by the corresponding linear analogues.In order to obtain stimuli-responsive hyperbranched polymers which combine both the advantages of advanced topological structure and multistimuli-responses,a variety of novel stimuli-responsive groups can be introduced into hyperbranched polymer chains by improving polymerization methods.Due to their controllable intelligent responsiveness,it has a wide range of applications in the fields of life sciences,sensors,environmental restoration,medicine and nanomaterials.Furthermore,to the best of our knowledge,there seems to be no report on the utilization of CO2 to cleave the pH-labile linkers or functionalities.Therefore,in this work,we attempt to incorporate CO2-acidolyzable dynamic iminophenylboronates into the backbone of hyperbranched poly(oligo(ethylene glycol))(hPOEG)with CO2-protonable tertiary amines as branched points,offering a gas-switchable LCST-type hyperbranched polymer(IB-hPOEG).The OEG-based branched monomer(OEG-BM)was prepared by a two-step ring-opening reaction of poly(ethylene glycol)diglycidyl ether(PEGDGE,Mn=394),3-amino-1,2-propanediol(APD)and cysteamine.Then,the target IB-hPOEG was prepared conveniently through the multi-component reaction of OEG-BM and 2-formylbenzeneboronic acid(FPBA).The chemical structures and properties of OEG-BM and IB-hPOEG were characterized by H-NMR,FT-IR and UV-vis spectrophotometer,etc.The results indicated that,upon alternative CO2 and N2,iminophenylboronates can be partially reversibly hydrolyzed and tertiary amines are repeatedly protonated.By varying the molar ratio of FPBA,polymer concentration or bubbling of CO2 and N2,the thermo-responsive behavior of IB-hPOEG aqueous solution can be well tuned with a much broad range of Tcp at 28～78℃ intervals.This gas-controllable LCST-type hyperbranched polymer with CO2-reversible iminophenylboronates has a promising potential for drug delivery,gene transfection,functional coatings,etc.