Borate-based Stimuli Responsive Polymer Studies

Stimuli-responsive polymer can respond to external stimuli of temperature,pH,light,redox,and so on,resulting in significant changes in their own structure and properties.It has a wide range of applications in the field of controlled drug delivery,biomedical material,environmental remediation,nano catalysis and sensors.In recent years,with further research,through the molecular design,incorporating a variety of stimuli-responsive moieties into the polymer chain can achieve the multifunctional materials,which has become a hotspot in the field of stimuli-responsive polymer materials.In this paper,we will focus on the single temperature stimuli response and the triple-stimuli response of pH,light and H2O2 to the borate-based polymer,respectively.(1)The UCST phase transition of polystyrene with quaternary ammonium salt-glycol borate.A quaternary ammonium salt-glycol borate styrene monomer of 4-vinylbenzyl-dimethylammonium-glycol borate(VMGB)was synthesized through the quaternization reaction,and the target UCST polystyrene(PVMGB)was synthesized by the free radical polymerization with AIBN as initiator and DMF/H2O(v/v,1/3)as polymerization solvent.The chemical structures of the monomer and the corresponding polymer were characterized by 1H-NMR,11B-NMR,SEC and TGA,and the optical transmittance of polymer aqueous solution was measured by UV-vis spectrophotometer to investigate the UCST phase transition behavior.It was found that the optical transmittance of PVMGB aqueous solution at room temperature declined linearly along with the increasing polymer concentration,ascribing to the increasing inter-molecular zwitterionic pairing in the polymer chain.Polymer aqueous solution upon heating and cooling exhibits no observable UCST behavior with the nearly constant optical transmittance itself.However,hydrobromic acidification of PVMGB aqueous solution afforded a reversible insoluble-soluble phase transition upon heating and cooling.(2)Iminoboronate multi-responsive amphiphilic polymer.The polymer of poly(ethylene glycol)-iminoboronate nitrobenzyl ethanediol chelate(PEG-INEC)was prepared via the aqueous iminoboronate multi-component reaction(MCR)of methoxypolyethylene glycol amine(mPEG-NH2),2-formylphenylboronic acid(FPBA)and bis(2-nitrophenyl)ethanediol(BNPE),and the amphiphilic polymer can be self-assembled to form polymer nano-aggregates in aqueous solution.Measurements of UV absorption and emission spectra,optical transmittance,DLS analysis,1H-NMR spectra and TEM observations were applied to track and analysis the stimuli-responsive dissociation reaction of amphiphilic polymer nano-aggregates.It was shown that amphiphilic polymer nano-aggregates can be dissociated when exposed to UV light,acid and H2O2,respectively,and the combined stimulation can greatly improve the dissociation efficiency.In addition,the drug release profiles of the amphiphilic polymer nano-aggregates were studied using DOX as the hydrophobic guest.It was shown that the responsive release behavior of polymer nano-carriers can be regulated by light,acidity,H2O2 and combined stimulation,and the combined stimulation can greatly accelerate the release of DOX.