1994 рік

Diffusion from one layer of a plasticized polymer film to the adjacent laminated layer is examined. Considering the importance of having a non-destructive, real-time method of monitoring interfacial diffusion, we developed a new spectroscopic technique. In the presented method, one of the two layers of a laminated polymer film is doped with electron-acceptor molecules, 2,4,7-trinitro-9-fluorenone, while the other layer contains a polymer with electron-donating side chains, poly(N-vinylcarbazole). As electron-acceptor molecules migrate to the adjacent layer, a charge-transfer complex is formed. The charge-transfer complex has a distinct optical absorption band, which is used in the presented technique to monitor its formation. The kinetics of charge-transfer complex formation is diffusion-controlled, and thus it is used to deduce diffusion coefficients of the mobile electron acceptor in various polymer matrices. The implementation of this technique in monitoring other transport processes is considered as well. Detailed mathematical modelling of the interlayer diffusion process based on the obtained experimental data is presented. Diffusivities found for 2,4,7-trinitro-9-fluorenone tracer in cellulose acetate butyrate, poly(vinyl acetate) and poly(vinyl butyrate) polymer matrices were 5 x 10 -9, 2.5 x 10 .9 and 2.5 x 10 .9 cm 2 s- 1, respectively. Diffusivities increase as diffusion from the laminated layer progresses owing to plasticizing of the matrix by the diffusing molecules.

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Cyclic near-tip stress fields which evolve ahead of fatigue cracks are known to have a pronounced effect on the fracture response of materials. This region of reversed damage is responsible for the initiation of fatigue cracks from stress concentrations under fully compressive cyclic loads, crack growth retardation following tensile overloads, and transient crack growth response under spectrum fatigue loading. By recourse to photoelasticity and laser interferometry, we provide direct and in situ measurements of cyclic near-tip stresses ahead of notches and fatigue cracks in amorphous polymers subjected to cyclic tension loading. The near-tip stresses are quantified during both the loading and unloading phases of the fatigue cycle, as well as during various stages of crack advance, in an attempt to establish a link between the evolution of near-tip stress fields and the advance of the fatigue crack. In addition, transmission electron microscopy analyses of the near-tip region have been performed to characterize cyclic deformation mechanisms.

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The pathway for polymerization of p-xylylenes is analysed at a theoretical level. The influence of the substituents on the aromatic ring on the conditions of the reaction is discussed on the basis of the Taft and Topson rules and Aq~ constants

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Compositions of several high-molecular-weight (>106gmo1-1) water-soluble copolymers have been determined using direct-polarization magic-angle spinning (d.p.m.a.s.) 13C nuclear magnetic resonance (n.m.r.). Comonomers were studied that comprised acrylamide and sodium 3-acrylamido-3-methylbutanoate, sodium 2-acrylamido-2-methylpropanesulfonate, diacetone acrylamide or isopropylacrylamide. A copolymer of sodium 2-acrylamido-2-methylpropanesulfonate and 2-acrylamido-2-methylpropanetrimethylammonium chloride was also included. The technique is rapid and provides copolymer compositional analysis with accuracies close to those obtained by conventional elemental analysis and solution n.m.r, techniques. Spectral resolution is excellent and d.p.m.a.s.n.m.r, allows shorter acquisition times and smaller sample size. The technique is applied to a variety of acrylamide copolymers including polyelectrolytes, polyampholytes and hydrophobically associating polymers. The results are compared to copolymer compositions obtained from elemental analysis and solution 13C n.m.r, spectroscopy

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Finite concentration inverse gas chromatography (i.g.c.) was used to determine the crosslink density of three poly(dimethylsiloxane) (PDMS) samples, which were crosslinked with different doses of ~,-rays. Crosslink density data of the same materials were also obtained in swelling measurements and, in one case, in stress-strain mechanical analysis. Results yielded by the different techniques agreed very well considering the different nature of the approximations made in the various experiments. Information obtained by i.g.c, also included the Flory-Huggins interaction parameters of the linear and crosslinked PDMS samples

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Polyacrylonitriles prepared by aqueous free-radical slurry polymerization using the potassium persulfate/sodium bisulfite redox initiation system have been examined by FT i.r. and high-field 13C and 1H n.m.r, spectroscopy. They have been shown to contain predominantly sulfonate and non-sulfur containing end-groups derived principally from initiation by bisulfite radicals and transfer to the bisulfite ion. Some sulfate end-groups are present also, although in much smaller amounts than the sulfonate end-groups, and are believed to arise from initiation by sulfate radical anions. In these respects, the polymers resemble closely those made by using ammonium persulfate/sodium metabisulfite as the initiator system

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The results of investigations into the cure of model anaerobic adhesives by measurements of the real and imaginary parts of the complex permittivity as a function of the cure time are reported. These adhesives are designed to exhibit heterogeneous cure which is initiated by the surfaces of two substrates on either side of a bondline. This situation is referred to as low cure through volume (CTV) or heterogeneous cure. Three stages in the cure process are identified and discussed. A physical model based on the Maxwell-Wagner interfacial polarization effect is given which satisfactorily explains the changes in the complex permittivity which occur due to the surface initiated redox cure of an anaerobic adhesive. The physical model is modified to explain the cure of another model anaerobic adhesive which is deliberately tailored to exhibit a much more homogeneous cure or high CTV. The model is found to fit the experimental data on the complex permittivity for frequencies up to 10kHz.

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The sulfonation kinetics of poly(oxyol,4-phenylene-oxy-l,4-phenylene-carbonyl-1,4-phenylene()P EEK) has been studied at highly dilute conditions (~ 0.02 g l-1) in 96.3% sulfuric acid. The sulfonation was observed from 35 to 75°C using ultraviolet-visible spectroscopy. The fractional sulfonation has been calculated from the ratio, I-Io/Io~-Io, where I, I0 and I® represent the spectral absorption of the reaction system at a time t, at the starting point and at the ending point, respectively. The I0 is extrapolated from a least-squares plot of the data calculated through a kinetic equation combined with the ratio cited above. The reaction rate was confirmed to be first order in the PEEK chain repeat unit and also inversely first order with respect to the concentration of the sulfonated PEEK repeat unit. The reaction follows the Arrhenius equation over the temperature range of study, with a calculated activation energy of 82.8 kJ mol- 1 repeat unit. Good agreement has been obtained between these results and the data measured in a more concentrated system (20 g PEEK/1 H2SO4).

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Solution terpolymerization of styrene, acrylonitrile and chromium acrylate has been carried out in dimethylformamide at 85°C using styrene arsenic sulfide complex as radical initiator. ~H nuclear magnetic resonance (n.m.r.), infra-red (i.r.) and elemental analysis have been used to characterize the terpolymer. Data from IH n.m.r., elemental analysis and gravimetric analysis have been used to evaluate terpolymer composition. Reactivity ratios (calculated from Finemann Ross method as r~(Sty)= 5 +2 r2(AN+CrA) = 0.15 + 0.02) and composition confirm its random origin. The terpolymer was highly thermally stable and has a glass transition temperature of 96°C as evaluated from differential scanning calorimetry studies

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The gas separation characteristics of isotactic polypropylene (iPP) thin films produced via the rolltrusion solid-state processing technique have been studied in order to establish some principles underlying permeation/separation behaviour in relation to membrane texture. Ideal and actual separation factors have been determined for various processing temperatures and draw ratios to assess the impact of the unique triaxial morphology produced during rolltrusion. Previously, we have shown that this unique morphological texture can improve the gas permeability of iPP by reducing the diffusive pathway tortuosity and by increasing the microvoid content in the polymer. In this study we show that the separation factors generally improve in iPP as a result of rolltrusion processing. However, the actual separation factors for a mixture of CO2 and Nz are less than the ideal values for all processing conditions studied, although this difference decreases with increasing draw ratio and decreasing processing temperature. This discrepancy between the actual and ideal separation factors is attributed to a depression in the permeability of CO2 in the mixture compared to the pure gas because of the presence of N 2.

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