No abstract

Hyperbranched fluoropolymers (HBFPs), based on benzyl ether linkages and having a large number of pentafluorophenyl chain ends, were crosslinked by a reaction with diamino‐terminated poly(ethylene glycol) (PEG) or diamino‐terminated poly(dimethyl siloxane) (PDMS) to form hyperbranched–linear copolymer networks of different compositions, structures, and properties. The crosslinking reactions involved the nucleophilic aromatic substitution of the pentafluorophenyl para‐fluorines of HBFP by the amine functionalities of the respective telechelic linear segments. The contact angles, differential scanning calorimetry, thermogravimetric analysis, tensile measurements, and atomic force microscopy (AFM) were used to characterize the resulting network film samples. The surface wettability of the crosslinked materials was affected by the nature and amount of the linear polymer crosslinking agent employed. Amphiphilic polymer networks were formed by the incorporation of diamino‐terminated PEG as a crosslinker, whereas diamino‐terminated PDMS produced polymer networks of a hydrophobic character. The mechanical properties improved upon crosslinking, as measured by tensile testing. The mechanical integrity of the films was also found to improve upon crosslinking, as measured by AFM machining protocols. The AFM images revealed topographical morphologies that appeared to be the result of phase segregation of HBFP from PEG or PDMS; the dimensions of the phase‐segregated domains were dependent on the stoichiometry of HBFP to the linear polymer and the thickness of the coating. As the content of PEG increased, fouling by human fibrinogen, used as a model protein, decreased. Further studies are in progress to determine the effects of the surface composition, morphology, and topography on the biofouling characteristics. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3531–3540, 2003

A hyperbranched polyfluorinated benzyl ether polymer was prepared from the A2B monomer 3,5-bis[(pentafluorobenzyl)oxy]benzyl alcohol. The polymerization was based upon deprotonation of the benzylic alcohol (B), followed by nucleophilic substitution of the p-fluorines of the two pentafluorophenyl (A) groups to form tetrafluorophenyl benzyl ether linkages. Optimized reaction conditions for the polymerization involved the addition of sodium metal (<0.1 mm particle size, 30 wt % suspension in toluene) to a solution of monomer (0.3 M) in THF heated at reflux. The molecular weight and molecular-weight distribution of the resulting polymer were affected by the surface area of the sodium particles, the concentration of the monomer, and the polymerization temperature. An average of one pentafluorophenyl chain end per repeat unit plus one pentafluorophenyl end group was present within the hyperbranched polymer, which allowed for chemical modification by nucleophilic displacement reactions upon the p-fluorines, to alter the physical and chemical properties of the material. Reaction of lithium trifluoroethoxide and lithium 1H,1H,2H,2H-perfluorodecanoxide with the pentafluorophenyl-terminated hyperbranched polymer introduced fluoroalkyl groups. Additionally, an X-ray opaque derivative was prepared by reaction of the pentafluorophenyl-terminated hyperbranched polymer with p-iodophenol. Contact angle measurements of water (96°, 99°, and 120°) and hexadecane (21°, 14°, and 62°) on films of a pentafluorophenyl-terminated hyperbranched polymer and the trifluoroethoxy-substituted and 1H,1H,2H,2H-perfluorodecanoxy-substituted derivatives, respectively, indicated a high degree of hydrophobicity and lipophobicity. Surface morphologies and surface properties of films were studied with atomic force microscopy (AFM). Tapping mode AFM images suggested phase separation in partially 1H,1H,2H,2H-perfluorodecanoxy-substituted material. Lateral force AFM (LFM) demonstrated that 1H,1H,2H,2H-perfluorodecanoxy substitution of the hyperbranched polymer led to a more than 2-fold decrease in the coefficient of friction and adhesive force, as measured with a silicon nitride probe.

Visual control has an influence on postural stability. Whilst vestibular, somatosensoric and cerebellar changes have already been frequency analytically parameterized with posturography, sufficient data regarding the visual system are still missing. The aim of this study was to evaluate the influence of pathologic and simulated visual dysfunctions on the postural system by calculating the frequency analytic representation of the visual system throughout the frequency range F1 (0.03-0.1 Hz) of Fourier analysis. The study was divided into two parts. In the first part, visually handicapped subjects and subjects with normal vision were investigated with posturography regarding postural stability (stability effect, Fourier spectrum of postural sway, etc.) with open and closed eyes. The visually impaired and the normal group differed significantly in the frequency range F1 (p = 0.002). Significant differences of the postural stability between both groups were found only in the test position with open eyes (NO). The healthy group showed a significant loss of stability, whereas the impaired group showed an increased stability due to sufficient somatosensoric processes. Visually handicapped persons can compensate the visual information deficit through improved peripheral-vestibular and somatosensoric perception and cerebellar processing. In the second part, subjects with normal vision were examined under simulated visual conditions, e.g., hyperopia (3.0 D), reduced visual acuity (VA = 20/200), yoke prisms (4 cm/m) and pursuits (pendulum). Changes in postural parameters due to simulations have been compared to a standard situation (open eyes [NO], fixation distance 3 m). Visual simulations showed influence on frequency range F1. Compared to the standard situation, significant differences have been found in reduced visual acuity, pursuits and yoke prisms. A loss of stability was measured for simulated hyperopia, pendulum and yoke prisms base down. Stability regulation can be understood as a multi-sensoric process by the visual, vestibular, somatosensoric and cerebellar system. Reduced influence of a single subsystem is compensated by the other subsystems. Obviously the main part of reduced visual input is compensated by the vestibular system. Moreover, the body sway, represented by the stability indicator, increased in this situation.

Matrix-assisted laser desorption/ionization (MALDI)-time-of-flight (TOF) mass spectrometry allowed direct determination of the extent of macrocycle formation that occurred during the polymerization and copolymerization of A2B and A4B monomers. Cyclization in hyperbranched pentafluorophenyl-terminated poly(benzyl ether)s was indicated by the presence of ions 20 Da less than the masses of acyclic species, owing to the loss of the HF chain ends during polymerization. This loss occurs by intramolecular nucleophilic aromatic substitution of the benzyl oxide focal point functionality upon a pentafluorophenyl chain end. Homopolymerizations and copolymerization of A2B and A4B monomers gave cyclic products in all cases, and the extent of cyclization depended on counterion, reaction time, and reaction temperature. In the copolymerization, product distributions revealed that larger proportions of A2B repeat units in the product led to increased amounts of cyclic products.