1999 рік

The miscibility, phase behavior, and intermolecular interaction of novolac/poly(e-caprolactone) (PCL) blends, before and after curing, were investigated by the high resolution solid-state nuclear magnetic resonance (n.m.r.) technique. It was found that there exists hydrogenbonding interaction between the carbonyl groups of PCL and the hydroxyl groups of novolac, which results in the downfield shift of carbonyl carbon resonance of PCL and the upfield shift of hydroxyl-substituted carbon resonance of novolac. The interaction also broadens the line width of carbonyl carbon resonance. After curing with 15 wt% hexamine (relative to novolac content), hydrogen-bonding interaction still exists between the components in the crosslinked blends. However, the relative amount of hydrogen bonds decreases significantly. Both the uncured and the cured novolac/PCL blends exhibit composition-dependent miscibility. The curing causes an increase of the domain size in the amorphous phase and a reaction of miscibility between the two components

Детальніше...  

Well-defined, fluorescence-free Raman spectra were obtained from native as well as treated (supercontracted) major ampullate dragline silks reeled from four very different spiders: Araneus diadematus, Nephila edulis, Latrodectus mactans and Euprosthenops sp. Conformational sensitive regions were assigned in the spectra. Compared to the silk of the silkworm Bombyx mori, all spider silks showed less b-sheet and more random coil and/or a-helix material. Polarized spectra suggested that the molecular chains of the spider silk were aligned parallel to the axis of the fibre. The differences in the mechanical properties between the native and supercontracted silks were attributed to variations in b-sheet content. The mechanism of contraction of spider silks in solvents was correlated to conformational changes in the supermolecular structure.

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Photoacoustic Fourier Transform infrared (PA FT-IR) depth profiling experiments ranging from 3 to 50 mm into the surface of thermoplastic olefin (TPO) show that the crystalline polypropylene (PP) phase resides at approximately 7–9 mm below the TPO surface, while ethylene-polypropylene rubber (EPR) layer is present at 15 mm, and extends into the bulk. In an effort to determine the distribution of PP and EPR components, a calibration method was developed by ratioing pure PP and EPR bands at 2953 and 2849 cm ⫺1 at 10/90, 25/75, 50/50, 75/ 25, and 90/10 ratios. Comparison of this numerical data and the experimental results allows determination of the distribution of EPR and PP components across the film thickness. It appears that the EPR region is predominantly present at 15 mm below the surface, while PP is located at shallower depths. Concentration variations of talc can be also followed by monitoring the band at 1019 cm ⫺1 caused by Si–O stretching modes and its content is higher near the TPO surface. Based on these studies, a stratification model for TPO is proposed.

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The effect of crosslinking by UV irradiation on the gas permeation properties of thin films (thickness > 1 mm) made from two benzophenone-based polyarylates were examined. In addition to the permeation response to UV crosslinking in these two polymers, the effects of crosslinking on the rate of physical aging was also explored. The sequence of physical aging and crosslinking, as well as reversal of the aging process was studied in order to separate the similar effects of aging and crosslinking. The results show that crosslinking very thin films can greatly improve the long-term performance of membranes when compared to noncrosslinked films of similar thickness.

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Copolymers containing 3-hydroxycyclohexyl methacrylate (HCMA) were synthesized as a base polymer for At-F excimer law lithography. The dry-etching rates of these polymers for CF4 CHF3 mixed gas were 1.1-1.2 times that of a novolac-based resist. The aclhcsion properties of the polymers were also studied by estimating the work of adhesion. When the content of the HCMA unit in the polymer cucccds 60 mol%, the work of adhesion of the resist is similar to those of polyvinylphenol (PVP)-based photoresists. A 0.19 pm pattern protile was obtained using a resist based on the terpolymer containing HCMA and the conventional developer, 2.38 wt% tetrarnethylammonium hydroxide (TMAH) aqueous solution.

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The orientation and deformation of polymer chains, in dilute solutions undergoing circular Couette flow, were measured by flow light scattering (FLS) techniques. Analysis of the angular dissymmetry of the scattered light intensity allowed the determination of polymer chain alignment in the flow direction, as well as a direct measurement of chain dimensions. The polymers were dissolved in several different solvents to determine the effect of solvent quality on polymer coil conformation under shear. The polymer solutions all consisted of a nearly monodisperse polystyrene sample of 3 х 10 6 g/mol molecular weight dissolved in various viscous solvents, including tricresyl phosphate, dioctyl phthalate, and a mixed solvent of low molecular weight polystyrene (M w ¼ 5780 g/mol) and dioctyl phthalate. There was a pronounced dependence of chain conformation on the quality of the solvent, with poorer solvents allowing more orientation of the polymers with the flow direction, as well as larger relative deformations.

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A series of poly(4-vinylpyridinium salts) was prepared by spontaneous polymerization of 4-vinylpyridine in the presence of various alkylating agents and at different temperatures in order to study by 1H-NMR the stereoregularity of the obtained polysalts. Contrarily to poly(4-vinylpyridine) which always gives an atactic structure, the polysalts were found to have an isotactic character. The observed isotactic triad content varies from 30%–50% and increase when the temperature of the polymerization decreases and with the hydrophobic character of the side chain. The preferential isotactic placement is explained in terms of the zwitterionic polymerization mechanism and the formation of a sandwich-like association between a quaternized monomer and the growing chain, an association stabilized by Coulombic interactions.

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Separation of low molecular weight polystyrene (PS) by temperature gradient interaction chromatography (TGIC) is reported. As in the separation of high molecular weight PS, temperature is an efficient variable to control the retention of low molecular weight PS in the reversed phase HPLC separation. However, a right choice of the eluent, typically a marginal solvent for the polymeric solute of interest, is crucial for the temperature to play an effective role in the retention control. For an example, PS oligomers were well separated by TGIC under the isocratic elution condition of C18 bonded silica and methanol as the stationary and the mobile phase, respectively.

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A simple approach is used to measure ihe reduced scattering coefficient us' ol a thick turbid medium having a small absorption coefficient uB' << uS'. Based on the light reflectance measurement ot semi-inhnite media by moans ot a CCD camera, the value ol shift Dx between the centre of the incident laser beam and the centre ot the dilïuse background is determined, which is inversely proportional to the uS'. The experimeiiial values of uS' determined lor fcPDM panicles in a polypropylene matrix are compared with model calculations using ihe Lorenz-Mie theory. A comparison ol theoretical data with parameters from image analysis of SEM pictures gives good accord.

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The morphology of ternary polystyrene/styrene–butadiene rubber/polyethylene (PS/SBR/PE) blends has been investigated in the limits of a constant content of the major component (PS; 75 wt%) while changing the weight ratio of the two minor constitutive polymers. A core– shell structure for the dispersed phase has been predicted from the spreading coefficients and observed by transmission electron microscopy. Actually, upon increasing the relative content of PE with respect to SBR, the structure of the dispersed phase changes from a multicore structure to a PE/SBR core–shell morphology. The size of the PE subphase in the mixed dispersed phase increases sharply at a PE content that corresponds to phase inversion in the parent SBR/PE binary blends. The ultimate mechanical properties of these blends are sensitive to the strength of the SBR interphase between PS and PE. Some synergism has been observed in the PE/SBR composition dependence of the tensile strengths at yield and break.

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