Controlled grafting of well-defined polymer brushes on the hydrogen-terminated Si(100) substrates (the Si-H substrate) was carried out via the surface-initiated atom transfer radical polymerization (ATRP). Surface initiators were immobilized on the Si-H substrates in three consecutive steps: (i) coupling of an ω-unsaturated alkyl ester to the Si-H surface under UV irradiation, (ii) reduction of the ester groups by LiAlH 4 , and (iii) esterification of the surface-tethered hydroxyl groups with 2-bromoisobutyrate bromide. Homopolymer brushes of methyl methacrylate (MMA), (2-dimethylamino)ethyl methacrylate (DMAEMA), and poly(ethylene glycol) monomethacrylate (PEGMA) were prepared by ATRP from the R-bromoester functionalized silicon surface. The chemical composition and topography of the graft-functionalized silicon surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. Kinetic studies revealed a linear increase in polymer film thickness with reaction time, indicating that chain growth from the surface was a controlled process with a "living" characteristic. Diblock copolymer brushes consisting of PMMA and PDMAEMA blocks were obtained by using the homopolymer brushes as the macroinitiators for the ATRP of the second monomer, providing further evidence to the existence of "living" chain ends. ATRP from the Si-H surfaces allowed the preparation of polymeric-inorganic hybrid materials with well-structured surface and interface.
Preparation of graft copolymers via living radical graft polymerization of poly(ethylene glycol)
methyl ether methacrylate (PEGMA) with poly(vinylidene fluoride) (PVDF) in the reversible addition−fragmentation chain transfer (RAFT)-mediated process was carried out. The peroxides generated on the
ozone-pretreated PVDF facilitated the thermally initiated graft copolymerization of PEGMA in the RAFT-mediated process. The chemical composition and structure of the copolymers were characterized by nuclear
magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, and molecular weight
measurements. The “living” character of the grafted PEGMA side chains was ascertained in the subsequent
block copolymerization of styrene. Microfiltration (MF) membranes were fabricated from the PVDF-g-PEGMA comb copolymers by phase inversion in aqueous media. Surface composition analysis of the
membranes by X-ray photoelectron spectroscopy (XPS) revealed a substantial surface enrichment of the
PEGMA graft chains. The pore size distribution of the resulting membranes was found to be much more
uniform than that of the corresponding membranes cast from PVDF-g-PEGMA prepared by the
conventional radical polymerization process in the absence of the chain transfer agent. The morphology
of the membranes was characterized by scanning electron microscopy. The pore size and distribution
varied with the graft concentration and the density of graft points. The PVDF-g-PEGMA MF membranes
displayed substantial resistance to γ-globulin fouling, in comparison to the pristine hydrophobic PVDF
MF membranes.
Controlled grafting of polybetaine brushes onto hydrogen-terminated Si(100) substrates (Si-H substrates) was carried out via surface-initiated reversible addition-fragmentation chain-transfer (RAFT) polymerization. The azo initiator was immobilized on the Si-H surface through a threestep process: (i) coupling of an ω-unsaturated alkyl ester to the Si-H surface under UV irradiation, (ii) reduction of the alkyl ester into a hydroxyl group by LiAlH 4 , and (iii) esterification of the hydroxyl group with the initiator 4,4′-azo-bis(4-cyanopentanoic acid) after acid chlorination. In the presence of the chain-transfer agent, RAFT-mediated polymerization of the sulfobetaine monomer N,N′-dimethyl(methylmethacryloyl ethyl) ammonium propane sulfonate (DMAPS) was initiated from the surface-immobilized azo initiator to produce DMAPS polymer (PDMAPS) brushes on the silicon substrate (Si-g-PDMAPS). X-ray photoelectron spectroscopy (XPS) analysis indicated that the PDMAPS brushes had been successfully grafted onto the silicon surface. Atomic force microscopy (AFM) images revealed changes in the surface topography of the silicon substrates and the presence of polymer overlayers. Ellipsometry results indicated that the thickness of the polybetaine film increased linearly with the polymerization time. The "living" characteristics of the end functionality of the polybetaine brushes from the RAFT-mediated process was ascertained by block copolymerization with the anionic monomer sodium 4-styrene sulfonate (SS) to form the diblock polymer brushes (a Si-g-PDMAPS-b-PSS surface).
Thermally‐initiated living radical graft polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) with ozone‐pretreated poly[N,N′‐(1,4‐phenylene)‐3,3′,4,4′‐benzophenonetetra‐carboxylic amic acid] (PAmA) via a reversible addition–fragmentation chain‐transfer (RAFT)‐mediated process was carried out. The chemical compositions and structures of the copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), and molecular weight measurements. The “living” character of the grafted PEGMA side chains was ascertained in the subsequent extension of the PEGMA side chains. Nanoporous low‐dielectric‐constant (low‐κ) polyimide (PI) films were prepared by thermal imidization of the PAmA graft copolymers under reduced argon pressure, followed by thermal decomposition of the side chains in air. The nanoporous PI films obtained from the RAFT‐mediated graft copolymers had well‐preserved PI backbones, porosity in the range of 5–17 %, and pore size in the range of 30–50 nm. The pores were smaller and the pore‐size distribution more uniform than those of the corresponding nanoporous PI films obtained via graft copolymers from conventional free‐radical processes. Dielectric constants approaching 2 were obtained for the nanoporous PI films prepared from the RAFT‐mediated graft copolymers.
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