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.

The relationships between the molecular aggregation states and water repellency of the perfluoroalkyl (R f ) groups of poly{2-(perfluorooctyl)ethyl acrylate} (poly-(FA-C 8 )) brush thin films with broad and narrow molecular weight dispersities (MWDs) were analyzed by grazing incidence wide-angle X-ray diffraction (GI-WAXD) and water contact angle measurements. MWD-controlled-poly-(FA-C 8 ) brush thin films were prepared by surface-initiated atom transfer radical polymerization on a flat silicon substrate in the absence and presence of an ionic liquid. In-plane diffraction profiles of poly(FA-C 8 ) brush films with narrow MWD had peaks corresponding to the periodic lengths of bilayer lamellae at q xy = 2−6 nm −1 . This indicated that the orientation of R f groups were parallel to the surface of the silicon substrate. In contrast, the peak of the in-plane GI-WAXD for brush films with broad MWD brush was confirmed at q xy = 12.5 nm −1 , indicating that the R f groups were oriented perpendicular to the surface of the silicon substrate. In the case of a poly(FA-C 8 ) brush thin film with a narrow MWD, the receding contact angle (θ R ) and sliding contact angle (θ S ) versus water were ca. 80°and 35°, respectively, whereas θ R and θ S were 105°and 15°, respectively, at the surface of poly(FA-C 8 ) with broad MWD. These results indicated that the water repellency of poly(FA-C 8 ) brush surface largely depends on the molecular aggregation state and orientation of the R f groups at the outermost surface and the MWD of the grafting polymer.

In patients with an implanted DDD pacemaker (PM), the atrial contribution may be interrupted by too short an atrioventricular (AV) delay, and filling time may be shortened by too long an AV delay. The AV delay at which the end of the A wave on transmitral flow coincides with complete closure of the mitral valve may be optimal. The subjects were 15 patients [70.3+/-12.3 (SD) years old] with an implanted DDD PM. Cardiac output (CO) and pulmonary capillary wedge pressure (PCWP) were measured by Swan-Ganz catheter. Transmitral flow was recorded by pulsed Doppler echocardiography. AV delay was prolonged stepwise by 25 msc. When the AV delay was set at 155+/-26 ms, the end of the A wave coincided with complete closure of the mitral valve. When the AV delay was prolonged 25, 50, 75, and 100 ms from this AV delay, the interval between the end of the A wave and complete closure of mitral the valve was prolonged 16+/-5, 39+/-6, 65+/-4 and 88+/-5 ms, respectively (r = 0.97, P<0.0001) and diastolic mitral regurgitation was observed during this period. Thus, the optimal AV delay may be predicted as follows: the slightly prolonged AV delay minus the interval between the end of the A wave and complete closure of the mitral valve. When the AV delay was set at 215 ms, there was a significant positive correlation between the predicted optimal AV delay (166+/-23 ms) and the optimal AV delay (CO: 161+/-26 msec, r = 0.93, P<0.0001, PCWP: 161+/-28 msec, r = 0.95, P<0.0001). In conclusion, optimal AV delay can be predicted by this simple formula: slightly prolonged AV delay minus the interval between end of A wave and complete closure of mitral valve at the AV delay setting.

ABSTRACT:SEC-MALS, small-angle X-ray scattering (SAXS), and viscosity measurements were made on tetrahydrofuran (THF) and n-hexane of a series of 4-vinylbenzyl and methacrylate ended poly(n-hexyl isocyanate) (PHIC) macromonomers (VB-HIC-n and MA-HIC-n, where n is a degree of polymerization of HIC and in a range from 21 to 192), together with higher molecular weight PHIC chains than the macromonomers. The molecular weight dependence of z-average mean-square radius of gyration hRg 2 i z and intrinsic viscosity [] of the macromonomers and PHIC chains in THF at 25 C were quantitatively described by the wormlike chain model with the stiffness parameter ð À1 Þ ¼ 63 nm, the molecular weight per unit contour length ðM L Þ ¼ 725 nm À1 , and the hydrodynamic diameter ðd B Þ ¼ 1:6 nm. The SAXS scattering profile of VB-HIC-57 in n-hexane at 25 C was also perfectly described in terms of the straight cylinder model. The results imply that the macromonomers may be regarded as a rigid rod molecule in THF and n-hexane. Cylindrical brushes consisting of polystyrene as a main chain and PHIC chains as a side chain were prepared by homopolymerizations of VB-HIC-46 and their dimensional properties were investigated in THF at 25 C by SAXS and SEC-MALS measurements. The molecular weight dependence of hRg 2 i z of the brushes was quantitatively explained by the wormlike cylinder model with the parameters of À1 ¼ 48 nm, M L ¼ 2:40 Â 10 4 nm À1 , the cross-sectional radius of gyration of the cylinder hRc 2 i o 1=2 ¼ 4:66 nm, and the end effect ( ¼ 16:7 nm) arising from side chains near the mainchain ends. It was concluded, therefore, that the main chain stiffness of the brush remarkably increases by the presence of densely located rodlike side chains. Direct observation of single brush of the poly(VB-HIC-46) deposited on a mica was made by scanning force microscopy (SFM) to reveal the cylindrical brushes consisting of rodlike side chains with ca. 15 nm in a thickness.

A well-defined cationic polymer and polymer brush were simultaneously prepared by coppercatalyzed atom transfer radical polymerization (ATRP) of 2-(methacryloxy)ethyltrimethylammonium chloride (MTAC) in 2,2,2-trifluoroethanol (TFE) at 60 °C initiated with ethyl 2-bromoisobutylate and the corresponding alkylbromide immobilized on silicon wafer. ATRP of MTAC in TFE as well as aqueous solution proceeded quickly but in a poorly controlled manner, leading to a relatively higher molecular weight distribution (MWD) than M w /M n = 1.3, where M w and M n are weight-average and number-average molecular weights, respectively. Addition of a small amount of isopropyl alcohol to the TFE-based reaction mixture reduced the polymerization rate and produced a poly(MTAC) with predictable molecular weight and narrower MWD than 1.19. The M n of poly(MTAC) was controllable in the range 10 4 -10 5 g mol -1 based on the molar ratio of monomer and initiator in the feed. The M n of the brush on a flat silicon wafer matched that of the free poly(MTAC). The graft density of poly(MTAC) was 0.20 chains nm -2 . The ATRP of MTAC in TFE/1-ethyl-3-methylimidazolium chloride (EMImCl) also proceeded in a controlled manner at 60 °C, yielding polymers with narrow MWDs (M w /M n = 1.12-1.13). Analysis of the 13 C NMR spectra of the carbonyl region of the resulting poly(MTAC)s revealed that syndiotactic-rich configurations were produced by ATRP of MTAC in aqueous solution, TFE/isopropyl alcohol, and TFE/EMImCl. The solvent effect of TFE and ionic liquid on the tacticity of polymer was negligible.