Zwitterionic polymers constitute a unique class of polyelectrolytes which have not been studied systematically because of the difficulty in their controlled synthesis and precise physicochemical characterization. The salt-concentration dependence of the chain dimensions and swollen brush structures of polyzwitterions, namely poly(2-methacryloyloxyethylphosphorylcholine) (PMPC) and poly[3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate] (PMAPS), in aqueous solutions of various ionic strengths was characterized by static light scattering, dynamic light scattering, atomic force microscopy (AFM), neutron reflectivity (NR), contact angle measurements, and macroscopic friction tests by sliding a glass ball under a load of 0.49 N. The hydrodynamic radius R H of PMPC was independent of NaCl concentration, whereas the R H of PMAPS markedly increased with the ionic strength. AFM and NR measurements also showed the independence of NaCl concentration of the swollen thickness of the PMPC brush in aqueous solution and significant changes in the swollen thickness of the PMAPS brush in aqueous NaCl solution. Both PMPC and PMAPS brushes showed oil detachment behavior in water and aqueous NaCl solutions. The PMPC brush had a significantly low friction coefficient (0.02-005) at a sliding velocity of 10 À2 to 10 À1 m s À1 in water even under a high normal pressure of 139 MPa.

Conformational properties of cylindrical rod brushes consisting of a flexible polystyrene main chain and poly(n-hexyl isocyanate) (PHIC) rod side chains have thoroughly been studied by static light and small-angle X-ray scattering (SAXS) in tetrahydrofuran (THF) at 25 °C. These rod brushes were prepared by radical homopolymerization of 4-vinylbenzyloxy-ended PHIC macromonomers (1) (VB-HIC-N s , where N s is the weight-averaged degree of polymerization of HIC and in a range from 21 to 80) in n-hexane at 60 °C. The mean-square cross-sectional radius of gyration (〈R c 2 〉 0 ) of the brush at an infinite dilution is determined by SAXS measurement and rationalized as a function of N s . The experimental value of 〈R c 2 〉 0 gradually increases with N s but above N s higher than 20 increases to follow the scaling law of 〈R c 2 〉 0 ∝ N s 0.87 . The experimental N s dependence of 〈R c 2 〉 0 is compared to that from the wormlike comb model whose main and side chains have different stiffness parameters. The molecular weight dependence of z-averaged mean-square radius of gyration (〈R g 2 〉 z ) of the brush is determined and analyzed in terms of the wormlike cylinder model taking into account the end effects. The parameters characteristic of the rod brush in THF solution, such as the main chain stiffness parameter (λ M -1 ), the molecular weight per unit contour length (M L ), and the excluded-volume strength (B), are determined and rationalized as a function of the contour length of the side rod. The polystyrene main chain stiffness of the rod brush remarkably increases by the densely located rod side chains to follow the scaling law of λ M -1 ∝ N s 1 . The backbone stiffness of the rod brush is higher than that of the flexible brush consisting of flexible polystyrene side chains with the corresponding contour length. A single rod brush of poly(VB-HIC-47) deposited on a mica surface is observed by the scanning force microscopy to reasonably demonstrate the cylindrical rod brushes.

The dimensions and intermolecular interactions of surface-grafted and unbound, free polyampholytes, poly [3-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate] (PMAPS) and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), were estimated in an aqueous NaCl solution over a wide range of salt concentrations (C s ). The free PMAPS and PMPC fractionated by a recycling preparative size-exclusion chromatography system were characterized in aqueous NaCl solutions for C s over a range from 0 to 5.0 M by static light scattering and dynamic light scattering (DLS) measurements. The hydrodynamic radius (R H ) and the concentration coefficient of the diffusion coefficient (k D ) for PMPC were independent of C s , whereas those for PMAPS were strongly dependent on C s . Monodisperse silica nanoparticles immobilized with PMAPS (SiNP-PMAPS) and PMPC (SiNP-PMPC) by surface-initiated atom transfer radical polymerization were characterized in aqueous NaCl solutions for C s over a range from 0 to 5.0 M by DLS and synchrotron radiation small-angle X-ray scattering (SAXS) measurements. The SAXS profiles from SiNP-PMAPS and SiNP-PMPC solutions were well described by the core-shell model, taking into account interacting self-avoiding chains and assuming a Schulz-distributed core with two fitting parameters.

Surface-initiated atom transfer radical polymerization (ATRP) of 2-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatoethanesulfonate) (MAES), 3-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate) (MAPS), and 4-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatobutanesulfonate) (MABS) was carried out in 2,2,2-trifluoroethanol (TFE) containing a small amount of 1-hexyl-3-methylimidazolium chloride at 60 °C to produce well-defined poly(sulfobetaine) brushes and the corresponding free polymers with predictable number-average molecular weight (M n, 1 × 104 to 3 × 105 g mol−1) and narrow molecular weight distributions (M w/M n < 1.2). A first-order kinetic plot for ATRP of MAPS revealed a linear relationship between the monomer conversion index (ln([M]0/[M])) and polymerization time. The polymerization rates decreased with increasing ionic liquid concentration. The M n of poly(MAPS) increased in proportion to the conversion. The sequential polymerization of MAPS initiated with the chain ends of poly(MAPS) produced the postpolymer with quantitative efficiency. The thickness of the polymer brush was controllable from 5 to 100 nm based on the M n of the polymer. The polymer brush was cleaved from the silicon substrate under the acidic condition to measure the molecular weight by size exclusion chromatography equipped with a multiangle light scattering detector (SEC-MALS). We have confirmed that the molecular weight distribution of polymer brush was also narrow (M n = 150 000, M w/M n =1.26) as well as the corresponding free polymer. These results suggest the successful control of the polymerization of sulfobetaine-type methacrylates owing to the TFE and ionic liquids. In particular, the high affinity of TFE for the sulfobetaine monomers and polymers yielded a homogeneous polymerization media to improve surface-initiated polymerization generating the polymer brushes on the substrate surface as well as the free polymers formed in the solution. The effect on ATRP of the chemical structure of ionic liquids and ligands for copper catalyst was also investigated.