Behavior and surface energies of polybenzoxazines formed by polymerization with argon,oxygen, and hydrogen plasmas

Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma‐polymerization technique with, as the energy source, plasmas of argon, oxygen, or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high‐energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties and morphologies in their surfaces. High‐energy argon atoms provide a thermodynamic factor to initiate the ring‐opening polymerization of BZZ and result in the polymer surface having a grid‐like structure. The ring‐opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma‐polymerization time. By estimating changes in thickness, we found that the PBZZ film synthesized by the oxygen plasma‐polymerization process undergoes the slowest rate of etching in CF₄ plasma. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4063–4074, 2004     

Preparation of benzoylchitosans and their chiroptical properties in dilute solutions

Two benzoyl substituted chitosan derivatives, 3,6‐O‐dibenzoylchitosan (DBC) and 2‐N‐3,6‐O‐tribenzoylchitosan (TBC), were prepared, and their optical activities in organic solvent were investigated by circular dichroism (CD). For TBC, two splitting bands (a negative one at 288 nm and a positive one at 274 nm) corresponding to the ¹L_b transition of the benzoyl group were observed in chloroform and dichloromethane, while only a negative CD band was recorded in N, N‐dimethylformamide (DMF). These results indicated that the transition moments of benzoyl groups were orderly arranged along the helical polymer chain when TBC was dissolved in a solvent with low polarity, but the same ordered structure did not appear in a polar solvent of DMF. For DBC, only negative CD signals corresponding to the ¹L_b transition of the benzoyl group were observed, regardless of the solvent property, which indicated that the chromophores were not arranged in an ordered fashion with appropriate geometry to interact with one another to induce bi‐signate CD signals. Adding methanol or DMF to the solution of TBC/chloroform resulted in a progressive decrease of the intensity of the positive split band at 274 nm. The intensity of the positive band was weakened upon heating a solution of TBC/chloroform from 20 to 60 °C. The results suggested that the ordered arrangement of the chromophores in the TBC system was dependent on solvent and sensitive to temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4107–4115, 2004     

Rheological and physical properties of aliphatic hyperbranched polyesters

The effects of the size (pseudo‐generation number) and nature of end groups on physical and rheological properties were investigated for a series of hyperbranched polyesters based on an ethoxylated pentaerythritol core and 2,2‐bis‐(hydroxymethyl)propionic acid repeat units. The observed linear dependence of the melt viscosity on the molar mass in the high pseudo‐generation‐number limit indicated that entanglement effects were substantially absent. Moreover, the marked influence of end capping of the end groups on the physical and rheological properties suggested that intermolecular interactions were dominated by contacts between the outer shells of the molecules, in which the end groups were assumed to be concentrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1218–1225, 2004     

Thermal behavior of metallodendrimers possessing bis(terpyridinyl)Ru(II) connectivity and different surface functionality

A series of metallodendrimers, assembled by means of bis(terpyridinyl)Ru^(II) connectivity on poly(propylene imine) dendrimer scaffolds, with homogeneous or heterogeneous surfaces, were prepared. Differential scanning calorimetry and thermogravimetric analysis were used to determine their thermal behavior, glass‐transition temperatures, and the decomposition kinetics and temperatures; no synergy effects for these properties were observed for the heterogeneously surfaced constructs in contrast to the corresponding homogeneously coated materials, which exhibited different values depending on their surface functionalities. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1487–1495, 2004     

Permeability of N2, Ar,He, O2, and CO2 through as‐extruded amorphous and biaxially oriented polyester films: Dependence on chain mobility

For as‐extruded amorphous and biaxially orientated polyester films based on poly(ethylene terephthalate), poly(ethylene naphthalate), and copolymers containing poly(ethylene terephthalate) and poly(ethylene naphthalate) moieties, permeability, diffusion, and solubility coefficients are interpreted in terms of chain mobility. The influence of polymer morphology is determined by comparison of the data for as‐extruded amorphous sheets and materials produced with different biaxial draw ratios. The crystallinities of the samples were assessed using differential scanning calorimetry and density measurements. Changes in mobility at a molecular level were investigated using dielectric spectroscopy and dynamic mechanical thermal analysis. The study, in conjunction with our earlier work, leads to the conclusion that the key to understanding differences in gas transport is the difference in local chain motions rather than in free volume. This was illustrated by the permeability results for He, Ar, N₂, and O₂ in the range of polyesters. However, the permeability of CO₂ was found to require alternative explanations because of polymer–penetrant interactions. For biaxially oriented samples, the differences in diffusivity are not only due to differences in local chain motions, but also additional constraints resulting from the increased crystallinity and chain rigidity—which also act to hinder segmental mobility. The effectiveness of the reduction in permeability in the biaxially oriented films is consequently determined by the ability of the polymer chains to effectively align and form crystalline structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2916–2929, 2004     

Viscosity,particle size distribution,and structural investigation of tetramethyloxysilane/2‐hydroxyethyl methacrylate sols during the sol–gel process with acid and base catalysts

The tetramethoxysilane (TMOS)/2‐hydroxylethyl methacrylate (HEMA) hybrid gels were synthesized with acid and base catalysts, via the in situ polymerization of HEMA, with and without the cosolvent methanol. With methanol in the TMOS/HEMA sol, the enhanced esterification and depolymerization reactions of the silanols resulted in a slower growth of silica particles. The silica particles that were synthesized with an acid catalyst were less than 40 nm. The thermal resistance of the poly(2‐hydroxyethyl methacrylate) (PHEMA) chains was enhanced by the addition of colloidal silica. The Fourier transform infrared characterizations and the exothermal peaks on the differential scanning calorimetry traces of these hybrid gels indicated chemical hybridization occurring as a result of condensation of the colloid silica and PHEMA at higher temperatures. Hence, the residual weight content of the hybrid gel after its synthesis with the base catalyst was even higher than the content of TMOS in the hybrid sol. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3476–3486, 2004     

Detection of Pb2+ using a hydrogel swelling microcantilever sensor.

Hydrogels containing benzo-18-crown-6 were used to modify microcantilevers for measurements of the concentration of Pb2+ in aqueous solutions. These microcantilevers undergo bending deflection upon exposure to solutions containing various Pb2+ concentrations as the result of a swelling of the hydrogels. It was found that a concentration of 10(-6) M Pb2+ can be detected using this technology. Other cations, such as Na+, have no effect on the deflection of this cantilever. The cation K+, which also complexes with benzo-18-crown-6, could interfere with Pb2+ detection, but only at high concentrations (> 10(-4) M).     

Resonance-stabilized phenoxy-like radicals formed by NO-mediated mono-nitration of coumarins containing a hydroxy group

Stable aminoxyls and an iminoxyl were observed by spin trapping and EPR techniques during the nitration of coumarins containing a hydroxy group by nitric oxide. The trapped free radicals are deduced to be the resonance stabilized phenoxy-like radicals. The mechanisms for the nitrations are suggested.     

A Quantum Chemical Study on Recognition of Nitro-phenols by Calix[n]arenes

A PM3 calculation in vacuum of the inclusion complexation ofo-, m-, p-nitro-phenol with calix[n]arenes is performedsuccessfully. The pathways for inclusion process are describedand the most probable structures of the 1:1 complex are soughtthrough a potential energy scan. The energy differences betweenthe inclusion complexes and the hosts, by calculation, show thatthe most stable complexation is calix[4]-p-nitro phenol andcalix[6]-m-nitro phenol.     

Cavitation mechanism in cyanobacterial growth inhibition by ultrasonic irradiation

To prevent cyanobacterial bloom in eutrophic water by ultrasonic method, ultrasonic irradiations with different parameters were tested to inhibit Spirulina platensis from growth. The experimental result based on cyanobacterial growth, chlorophyll a and photosynthetic activity showed that, the ultrasonic irradiation inhibited cyanobacterial proliferation effectively, furthermore the inhibition effectiveness increased in the order: 200 kHz>1.7 MHz>20 kHz and became saturated with the increased power. The inhibition mechanism can be mainly attributed to the mechanical damage to the cell structures caused by ultrasonic cavitation, which was confirmed by light microscopy and differential interference microscopy. The optimal frequency of 200 kHz in cavition and sonochemistry was also most effective in cyanobacterial growth inhibition. The higher frequency of 1.7 MHz is weaker than 20 kHz in cavitation, but has more effective inhibition because it is nearer to the resonance frequency of gas vesicle. The inhibition saturation with ultrasonic power was due to the ultrasonic attenuation induced by the acoustic shielding of bubbles enclosing the radiate surface of transducer.