Studies Of Polymer Brushes Fabricated By Photopolymerization

Synthesis of polymer brush has been studied widely in these years because of their potential application in many fields including biocompatible surfaces, biomaterials for tissue engineering, drug delivery, controlled adhesion and wetting, protein recognition, molecular recognition, microfluidics, chemical sensing and organic synthesis. Our study is focused on the fabrication of polymer brush by photopolymerization.A well-defined, high-density Poly(N-isopropylacrylamide) (PNIPAM) brush was fabricated through a novel and reliable strategy by combination of self-assembly monolayer of dendritic photoinitiator (SAM) and surface-initiated photopolymerization. Growth process of PNIPAM brush was confirmed by water contact angles (WCA), X-ray photoelectron spectroscopy (XPS) spectra and atomic force microscopy (AFM). Characterization of PNIPAM brush such as molecular weights and thickness was measured by gel permeation chromatography (GPC), ellipsometer and graft density was estimated. The result shows that it is easy to get PNIPAM brush of more than 100 nm thickness after one-hour UV-irradiation. The temperature response of PNIPAM brush was further investigated by water contact angle (WCA) and AFM. The WCA on PNIPAM brush changed from 68 o to 82 o below and above LCST reversible. AFM result verified the coil–to-globule transition of PNIPAM chains in water from low to high temperature.Taking advantage of the photobleaching and co-initiating properties of the dendritic thioxanthone (TX) photoinitiator, we developed a general and facile approach to fabricate patterned binary polymer brushes by combining photolithography and surface initiated photopolymerization(SIPP). The dendritic TX photoinitiator monolayer was immobilized covalently on a silicon slide surface, followed by photobleaching through a mask. The resulting slides could initiate photopolymerization of methyl methacrylate (MMA) to generate a patterned poly (methyl methacrylate) (PMMA) brush, and subsequently initiate styrene (St) in the presence of TX to obtain patterned binary poly (methyl methacrylate)-polystyrene (PMMA-PS) brushes. This general and facile method could be of use in large-scale patterned binary polymer brush fabrication.Multi-stimuli responsive poly (ether amine) (PEA) was successfully grafted on the planar silicon through a convenient and efficient way via"thiol-ene"click chemistry. The whole process for fabrication of PEA brush was carefully traced by XPS, AFM, ellipsometer and water contact angle (WCA). The results indicated that PEA brushes with different thickness can be obtained through both photochemical and thermal processes. The obtained PEA brush in aqueous solution exhibited its response to temperature and pH value. With the increase of pH and temperature, the PEA chain became less hydrophilic and adopted the coil-globule transition. And the obtained PEA brush exhibited great resistance to protein. Resistance of nonspecific protein is an important concept in biomedical fields since it allows regulation of tissue adhesion and blood coagulation on the surfaces of various important biomaterials. we continued to graft PEA-SH on the planar nobel metal surfaces to study the protein resistance of PEA brush. The strategy is illustrated in Scheme 1 and the growth of PEA brush was carefully traced by XPS, ellipsometer and WCA. The protein resistance of PEA brush was further investigated by FIM and XPS. We found that this approach to fabricate PEA brush on nobel metal was very fast and efficient.