1993 рік

Characterization of the water structure in hydrogels is of the utmost importance in understanding their dynamic and equilibrium swelling behaviour as well as in analysing solute transport and other diffusive properties of such systems. Polymer-water interactions coupled with the physical property changes of the water associated with the hydrogel structure can determine the permeability characteristics of solutes through these hydrogels. The water structures inside ionic copolymeric networks of poly(2-hydroxyethyl methacrylate-co-methacrylic acid) and poly(2-hydroxyethyl methacrylate-co-acrylic acid) were investigated as a function of the pH and ionic strength of the swelling medium and the type of counterion in the swelling medium using differential scanning calorimetry. The free water content increased with an increase in pH and a decrease in ionic strength. The bound water content was found to be independent of the pH of the external swelling medium. The Donnan ionization equilibrium concept was used to explain the observed trends. This study is useful in correlating the hydrogel water structure with solute diffusion through these hydrogels

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Doped-poly(ethylene oxide)-coated minerals (e.g. talc, calcium carbonate) can be used as light-coloured conductive fillers to produce charge dissipative polymer composites.

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Notched specimens, composed of layers of pure nylon and layers of nylon-EPR blend, were prepared. The specimens were fractured in an Izod impact test and were also fractured in tension, with the draw speed set to give a strain rate comparable to that of the Izod impact test. The data show that at these high deformation rates a brittle propagating crack can be stabilized when it reaches the ductile material (the blend).

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The overall isothermal crystallization kinetics for isotactic polypropylene (iPP) in dotriacontane was investigated. Half-time was determined via differential scanning calorimetry as a function of the experimentally-controlled variables, dilution and crystallization temperature. Polymer concentration was varied from 100 to 10 wt% iPP in 10wt% intervals. Crystallization temperature was varied from 415 to 380 K in 1 K intervals. The influence of these variables on crystallization mechanism and spherulitic structure, as implied by the Avrami analysis, was determined, and their influence on fold surface energy was exained by the Lauritzen and Hoffman analysis.

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The branching characteristic of the spherulites of poly(ether ether ketone) (PEEK) has been studied. The spherulitic branching texture was apparent under optical microscope when the PEEK films were very thin, when PEEK had been crosslinked to some extent, or when another amorphous polymer was added to PEEK. Various branching angles are possible in the fibrillar branching growth of the spherulites.

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Three poly(aryl ether ketone)s (PAEKs) were melt blended at 415°C with a new thermoplastic polyimide (N-T PI) composed of (4,4'bis(3-aminophenoxy) biphenyl) and pyromellitic dianhydride. The PAEKs studied were poly(aryl ether ether ketone) (PEEK), poly(aryl ether ketone ketone) (PEKK) and poly(aryl ether ketone) (PEK). Although chemically similar, these three show distinctly different behaviour when blended. We have concentrated on amorphous blends in this work so the difference in the crystallization rates of the PAEKs is not a factor in our determination of miscibility. It was found that PEEK was immiscible with N-TPI at all proportions. PEKK is the slowest crystallizing polymer and is miscible at most proportions, as evidenced by single glass transitions. PEK is miscible at N-TPI contents of less than ~ 50% and partially phase separated in the N-TPI rich blends. It is apparent that the higher percentage of ketone linkages in the PAEKs correlates with the higher degree of miscibility. Charge transfer complexation could also be a factor but this has yet to be explored.

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The heterogeneous nucleation of polypropylene homopolymer and discontinuous glass fibre (critical fibre length, L? >~ 3 mm) reinforced polypropylene was performed by using sodium benzoate as the nucleating agent. Isothermal crystallization of the compression-moulded nucleated polypropylene, non-nucleated polypropylene, nucleated composite and non-nucleated composite was carried out over a temperature range of 370-398 K. Comparison of the shift in the bulk crystallization peak temperatures, as well as the rate of isothermal crystallization of the samples, showed that the incorporation of the nucleating agent resulted in a significant improvement in the crystallization of the polypropylene homopolymer. The short glass fibres nucleated the polypropylene matrix to the extent that the crystallization and morphology of the matrix differ appreciably from those of the homopolymer. Detailed Avrami kinetic analysis was carried out at 390 K for the samples and values of the Avrami constants K and n, ranging from 2.3 x 10 5 to 2.4 x 10 -3 and 2.01 to 1.66 for the polypropylene homopolymer to the nucleated composite, respectively, were obtained. Optical microscopic analysis showed spherulitic crystallization for the homopolymer, crystallitic crystallization for the nucleated polypropylene, and mixed crystallitic and axialitic crystallization for the discontinuous composite.

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Ellipsometry is used to obtain the first measurements of the adsorption kinetics and adsorption isotherm of a doubly end-attaching polymer. A triblock copolymer of poly(ethylene oxide)-polystyrene-poly(ethylene oxide) is adsorbed onto silicon dioxide from toluene; only the polar-end blocks adsorb. At short times, the kinetics of adsorption follow Fickian behaviour. At small bulk concentrations, the surface saturation is approached monotonically but as the bulk concentration is increased an 'overshoot' in the adsorbed amount is observed. The adsorbed amount of triblock copolymer is less than the amount found for a corresponding diblock copolymer. This difference is attributed to the presence of triblock copolymers adsorbed in a loop-like conformation.

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Steady state fluorescence was used to examine the interdiffusion of polymer molecules during annealing of a latex film at and above the glass transition temperature. The film was prepared from a mixture of poly(methyl methacrylate) latex particles labelled with naphthalene (donor) and pyrene (acceptor). It was observed that the optical density (index of refraction) of the latex film changed considerably during the annealing process. Donor and acceptor intensities were required to compensate for this effect. The activation energy for polymer chain interdiffusion was found to be 34 kcal mol 1

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We investigated the spherulite growth rate (G) in a 40/60 isotactic polypropylene (PP)/liquid paraffin (LP) mixture under a polarized microscope with a TV video recording system. The molecular weight of LP (M) was changed. Subtracting the supercooling contribution from the overall G, we obtained the chain mobility (fig) factor, as a function of M and crystallization temperature (To). As T~ increased, a transition from regime III to II was found to occur. An Arrhenius plot of the fig term showed that the activation energy in regime II is much larger than that in regime III, suggesting different diffusion modes. The fig term in regime III was found to depend strongly on M (fls~:M-1), indicating a mutual-diffusion mode. In contrast, the fls term in regime II weakly depends on M, indicating a self-diffusion mode (flg~:M-1/2).

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