1999 рік

The inverse gas chromatography method was utilized to obtain the thermodynamic properties and the surface energy of a semicrystalline polymer, poly(ethylene oxide) (PEO). PEO was used as a stationary phase in the chromatographic column and 16 solutes with a different chemical nature were used as eluents such as alkanes, acetates and alcohols. Each family has provided information on the type and strength of the PEO–solute interactions. Alkanes showed endothermic interaction parameters x 12 and the molar heat of mixing in a temperature range of 70–130°C. Acetates and alcohols showed better interactions with the PEO layer and butanol was found to be the best solvent for PEO among all solutes used. The variation in molecular weight of PEO above 4000 g mol ¹1 showed no apparent effect on the interaction coefficients. The dispersive contribution of the surface energy of PEO was measured as a function of temperature, which ranged between 8.00 and 13.00 mJ m ¹2, indicating a poor surface energy of PEO.

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The miscibility of a ternary system of poly(3-hydroxybutyrate), poly(ethylene oxide) and polyepichlorohydrin was studied by differential scanning calorimetry. The three binary blend systems are individually miscible. All the ternary blends were found to be miscible as shown by the existence of a single glass transition temperature in each blend. The interaction parameters of the three binary pairs are of similar magnitude and do not lead to a “Dx ” effect.

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We present a finite chain-length calculation of the rubber elasticity of an isotropic crosslinked network of freely jointed chains under affine deformation. Whilst this is a classical calculation, the result is derived in its full tensorial structure for the first time, and new predictions of non-Gaussian elasticity for general biaxial deformations are presented. The full tensorial rubber-elasticity derivation allows any deformation regime to be treated, to facilitate validation with experimental data. Even though more complex many-chain effects are neglected, this theory appears to be the only one to offer a physical explanation for negative values of W 2 observed experimentally at small strains.

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The sorption and kinetics of acetone uptake in solvent cast films of poly(ethylene terephthalate) are reported at 35°C for acetone pressures ranging from 0 to 7.3 cm Hg. The equilibrium sorption isotherm is well described by the dual-mode sorption model with the following parameters: k D ¼ 61 cm 3(STP)/(cm 3·atm), CH⬘ ¼ 7:2 cm3 (STP)=cm3 , and b ¼ 50 atm -¹. Sorption kinetics are described using a two-stage model which incorporates both Fickian diffusion and protracted polymer structural relaxation. The characteristic time associated with the relaxation process is essentially independent of acetone concentration and has an average value of approximately 15 hours. The fraction of sorption associated with polymer relaxation increases linearly with acetone concentration in the equilibrium-densified matrix of the polymer. Acetone diffusion coefficients increase with increasing acetone concentration. The concentration dependence of the acetone diffusion coefficient is well described by the dual-mobility model if the assumption of constant diffusion coefficients in the two modes is relaxed.

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Light scattering and viscometric measurements were made on ternary mixtures of high molecular weight polyacrylamide (PAM), and the nonionic surfactant, Triton X-100 (TX-100) in aqueous solution. The binary solutions of polymer and surfactant in aqueous media were also studied. In the ternary system, the solution viscosity and translational diffusion coefficients were determined at 308C in terms of (a) the surfactant concentration at fixed PAM concentration, (b) the PAM concentration at fixed surfactant concentration, and (c) the PAM molecular weight. The surfactant concentration was varied by five orders of magnitude, the mean diffusion coefficient decreased slightly at first until reaching a minimum and then rose toward an asymptotic value which was identical to that of a single micelle. Near the cmc, the binding of the surfactant onto a polymer chain induced a slight chain expansion, but surprisingly the specific viscosity diminished. DLS shows a component owing to free micelle diffusion at concentrations above 1 mM of TX-100. This indicates the saturation point of binding between PAM and TX-100. Different molecular weights of PAM interacted with the surfactant quite similarly.

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The effect of the solvent composition on the conformation of a super high molar mass polyelectrolyte, M w ¼ 22–25 х 10 6, dissolved in a water–acetone mixture was investigated using static and dynamic light scattering. When increasing the concentration of acetone above 80 mass percent, a reversible conformational change of macromolecules occurs, which causes a sharp decrease in the viscosity, a rise in the light scattering intensity, and also a decrease in the radius of gyration, R g, the hydrodynamic radius, R h, as well as in the second virial coefficient A 2. The correlation function measured by dynamic light scattering changes from bimodal to unimodal indicating the formation of compact globular structures.

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The crystallinity of poly(ethylene terephthalate) (PET) films was investigated by comparing measurements of fluorescence, differential scanning calorimetry and density. It was found that the ratio of the fluorescence intensity at 330 nm to that at 370 nm can be an effective indicator of crystallinity. The dynamic process of recrystallization was directly observed for PET prepared using a spin-casting method on quartz disks by means of fluorescence measurements at several temperatures between 380 and 400 K. The recrystallization of such films was found to proceed one-dimensionally under the mechanism of heterogeneous nucleation, since the Avrami exponent, n, was determined to be one. The apparent activation energy of recrystallization was determined to be 120 kJ/mol, indicating that more than a few monomer units of PET participate in reorientation and crystallization. The present work should provide a quick and nondestructive method for determining the crystallinity of PET factory products.

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Poly(chloro-p-xylylene) thin films are shown to have a changing morphology as a function of deposition temperature from spectroscopic ellipsometry and X-ray diffraction measurements. At lower deposition temperatures, the as-deposited polymer exhibited negative birefringence attributed to the presence of amorphous conformationally disordered polymer chains. As the deposition temperature was increased the polymer chains became more conformationally ordered resulting in an increase in the thin film’s birefringence. At higher deposition temperatures, above the polymer’s Tg evidence of crystallinity was apparent from X-ray diffraction results. The increase in the thin film’s birefringence may be attributed to the thermodynamic driving force for crystallization causing the plane of the phenyl group to orient more perpendicular to the plane of the substrate, evidently the more stable conformation for poly(chloro-p-xylylene). After an inert post-deposition anneal at 2108C for 2 h, the thin films deposited at lower temperatures showed evidence of higher crystal quality than the above Tg deposited films because of a smaller d-spacing. A decrease in the full width half max of the X-ray diffraction peak was attributed to a large increase in the crystallite size, larger for the films deposited at higher temperatures as a result of a greater degree of crystallinity present in those films asdeposited. Further, comparisons are made between the as-deposited and post-deposition annealed samples in terms of stress, crystalline disorder and crystallite size. In addition, from differential scanning calorimetry measurements, the glass transition temperature of poly (chloro-p-xylylene) was 358C–368C and 448C at heating rates of 0.28C/min and 58C/min.

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A comparative study of the different relaxations present in poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) is carried out by thermally stimulated depolarization current (t.s.d.c.), dynamic mechanical analysis (d.m.a.) and dynamic electric analysis (d.e.a.). In the temperature range from ¹ 150 to 200°C, PEN shows four relaxations located, in increasing temperature order, around ¹ 70°C (b), 60°C (b*), 130°C (a) and 170°C (r). The two sub-glass transition relaxations detected are attributed to dipolar motions of the polymer chain and their origin is discussed. Above the glass transition (a relaxation) the r peak is shown to be of non-dipolar origin and associated with free charge detrapping in the material. The kinetic parameters of the relaxations observed by these techniques in the aforementioned temperature range have been determined by fitting the experimental data to standard models. The activation energies calculated in this way vary from 0.5 eV for the b relaxation to 2.2 eV for the r relaxation. The b* and a relaxations are distributed and it is shown that they follow the compensation law.

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The usual approach that is used to characterize the molecular orientation in biaxially oriented samples by infrared spectroscopy is to measure spectra with polarization in all three directions: machine, transverse and normal (or thickness). However, the latter measurement is rather difficult to make experimentally. In the present work we propose a new approach to characterizing the molecular orientation in both uniaxially and biaxially oriented samples of PET, based on the use of front-surface reflection spectra. It makes use of the ratio of the absorption bands at 1330–1240 and 1729 cm -¹, the first of which shows parallel dichroism and the second perpendicular dichroism. An equation is developed that relates this ratio to the molecular orientation with respect to the direction of measurement. Thus, it is possible to determine individually the orientation functions with respect to the machine and transverse directions. The validity of functions determined in this way is confirmed by comparison with birefringence results. Crown copyright

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