CO₂-responsive Spherical Polyelectrolyte Brushes:Synthesis,Properties And Application

CO₂-responsive polymers have received special attention because of the advantage of using CO₂ as a trigger.CO₂ is a non-toxic,benign,cheap and abundant gas.It is also an important metabolite in the cells,which has good biocompatibility and membrane permeability.Spherical polyelectrolyte brushes?SPBs?are latex particles consist of a polyelectrolyte shell grafting densely on the core,and this stable colloid systems can be designed responsive to stimulations through functional polymer chains and a modified cores.Due to the special properties of SPBs,it could be used as carrier system or nano-reactors for synthesis of metal nanoparticles,drug control and protein carrier.In this work,the multi-sensitive SPBs consisting of a PS?polystyrene?core and a shell of poly-?2-?dimethylamino?ethyl methacrylate?PDMAEMA were synthesized by photoemulsion polymerization,and it was employed to bind bovine serum albumin?BSA?for enrichment and separation of protein.More importantly,owning to the tertiary amine groups in PDMAEMA,the PDMAEMA brush could release the protein not only by traditional methods such as adjusting the pH or increasing the ionic strength of the solution,but also by bubbling the nontoxic and good biocompatibility gas,CO₂,which can also easily be removed just passing through the inert gas like N2 or Ar without any accumulation of salt in the system.In addition,this nanoparticle could be employed as a kind of switchable surfactant in the n-dodecane-water composed Pickering emulsion with CO₂/N2 as a trigger.The main works and results are summarized as following:1.A novel multi-responsive SPB,PS-PDMAEMA was proposed,which composed of PDMAEMA as shell and PS as a solid spherical core through photoemulsion polymerization.The uniform distributed PDMAEMA brushes are a kind of weak cationic polyelectrolyte chains which could responsive to the simulation of pH,ionic strength and the temperature,respectively.Employed these effectors as co-triggers,this brush showed considerable ability to capture and release proteins through electrostatic interactions with different characterization,such as dynamic light scattering?DLS?,zeta potential and isothermal titration calorimetry?ITC?,etc.Based on the experimental results,PS-PDMAMEA is promising for applications in protein purification and selective immobilization of proteins,enzymes and antibodies.2.Based on the first part of work,the property of CO₂-responsive of PS-PDMAEMA has been employed in the experiment of enrichment and separation of protein.The brush exhibited collapsed and extended states by bubbling with the N2 and CO₂ gas into the aqueous solution,respectively.Due to these properties,the gas-controllable brush allowed the cycles of binding and releasing protein repeated several times without salt accumulation.Both UV-vis and circular dichroism spectroscopy?CD?could also be employed to prove the proteins retain their biological activity after releasing from the brush layers.Different characterization all confirmed that this multiple responsive brush could be an effective and green candidate on protein immobilization and separation.3.PS-PDMAEMA could enhance the performance of n-dodecane-water composed Pickering emulsion with CO₂/N2 as a trigger.DLS,conductivity measurement,digital photography as well as polarizing microscope have been used for characterization of the emulsifying performance of PS-PDMAEMA microspheres.The results confirmed that the Pickering emulsion could be formed as input of N2 as well as the emulsion could be broken as input of CO₂.With the help of CO₂/N2,the properties of the system could be adjusted reversibly many times without any salt accumulation.It also could broaden the usage of CO₂ as a green stimulation.