Preparation Of PEGMA Brushes By Laser-Mediated SI-ATRP Polymerization

The light-mediated surface-initiated atom transfer radical polymerization(SI-ATRP)is a technique combining the light stimulus response and ATRP controlled radical polymerization characteristic to prepare patterned polymer brushes,which have a broad application prospect in medical and biological fields.This paper prepared the patterned Poly(ethylene glycol)Methacrylate(PEGMA)brushes by laser-mediated SI-ATRP with tris(2-phenylpyridine)iridium(III)(Ir(ppy)3)catalytic system.The instruments,including ellipsometer,XPS,LSCM and optical microscope,were used to characterize the brush growth,chemical composition,protein adsorption resistance and micropattern structure.The effect of catalyst concentration,light intensity,monomer concentration and initiator grafting density on the growth curve of PEGMA brushes were discussed.Based on the discussion of laser-mediated SI-ATRP process in Ir(ppy)3 catalytic system,radical "migrate" termination model and initial linear termination model were proposed.According to the curve fitting,the relationship between the activator Ir?*to deactivator Ir? ratio as well as the chain termination rate constant kt and different reaction conditions were discussed.The following results have been achieved:(1)Laser source greatly improved the preparation efficiency of PEGMA brushes compared with LED source in light-mediated SI-ATRP system.By using a photomask with 50?m interval stripes pattern,the pattern prepared by laser-mediated SI-ATRP had clear boundry and the patterned PEGMA brushes could resist the protein adsorption well.(2)The influence of catalyst concentration,light intensities,monomer concentrations and initiator grafting densities on PEGMA brushes growth were studied by ellipsometer.The steady-state quenching process of Ir(ppy)3 was investigated by fluorescence spectroscopy.It was found that the ratio of activator Ir?*to deactivator Ir? in Ir(ppy)3 catalytic system was independent of time.(3)According to the mechanism of Ir(ppy)3 catalytic system,the formula of reaction kinetics of light-mediated SI-ATRP was derived.The radical "migrate" termination model and initial linear termination model were proposed based on the surface radical "migrate"termination mechanism to depict the surface initiated radical polymerization process.The ratio of of activator Ir?*to deactivator Ir? and the chain termination rate constant kt were used to evaluate the kinetics of polymerization process.(4)The radical "migrate" termination model and initial linear termination model were used to fit the PEGMA brushes growth curves under different catalyst concentration,light intensitiy,monomer concentration and initiator grafting density conditions.Due to the competition between radical "migrate" termination and living propagation,the radical"migrate" termination model could fit the smooth stage well,while the initial linear termination model could fit the transition zone of growth curve well.(5)The linear relationship between ?? and[Ir?]/[Ir?]could indirectly describe the catalytic system state.[Ir?*]/[Ir?]increased along with the arise of catalyst concentration,monomer concentration,light intensity and grafting density.In the radical "migrate"termination model,[Ir?*]/[Ir?]was proportional to[I]oa and grafting density.In the initial linear termination model,[Ir?*]/[Ir?]was proportional to[C]0b,[I]0c,monomer concentration and grafting density.(6)kt was used to describe the trend of chain termination in SI-ATRP process.The value of kt decreased slightly with the increase of light intensity,monomer concentration,grafting density.While for catalyst concentration,the influence on kt is different:In the radical"migrate" termination model,increasing the catalyst concentration would decrease the value of kt which would decrease the trend of chain termination,while the initial linear termination model had an opposite trend that increasing the catalyst concentration would increase the value of kt.