1993 рік

Chemiluminescence imaging was successfully carried out for some polymer materials under heating or mechanical stress using a two-dimensional photoelectron detector. Oxidative degradation could be visualized for the press-moulded sheets of Nylon 6 (Ny6) and polystyrene (PS), and for the multilayered sheet composed of polyethylene (PE) and styrene-butadiene triblock copolymer (SBS) by heating samples at 50-154°C in air. The chemiluminescence intensity varied over the surface of the sample specimen; the surface trimmed with a razor blade and the cracked portion exhibited especially strong luminescence for Ny6 and PS samples. The difference in the oxidation reaction rate between the two kinds of materials could be visualized clearly for the multilayered sheet of PE and SBS. Stress-induced luminescence was observed on drawing Ny6 at room temperature, and it was found that the luminescence was remarkably strong around the stress-concentrated part of the specimen.

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Miscibility and phase behaviour in blends of poly(p-fluorostyrene) (PpFSt), poly(o-fluorostyrene) (PoFSt), poly(p-chlorostyrene) (PpCISt), poly(o-chlorostyrene) (PoC1St), poly(p-bromostyrene) (PpBrSt) and poly(o-bromostyrene) (PoBrSt) with partially sulfonylated poly(2,6-dimethyl-l,4-phenylene oxide) (SPPO) copolymers [i.e. systems of the type (A),J(CI_rDy),2] have been studied by d.s.c, as a function of temperature and degree of sulfonylation. For all the para-substituted styrene polymers/SPPO blends studied, limited miscibility regimes are found. A miscibility regime is also found for PoFSt/SPPO blends. However, PoC1St and PoBrSt are not miscible with any SPPO. Using the mean-field approach, we have calculated all the pertinent segmental interaction parameters for these blends. In several systems, certain blends have been found to exhibit lower critical solution temperature behaviour

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The microstructures of hydrogenated polybutadienes produced using different hydrogenation routes, namely the low-temperature hydrogenation using tris(triphenylphosphine)rhodium0) chloride or platinum black catalysts, have been studied by Raman spectroscopy. The same spectroscopic method has also been used to examine the products formed by a hydrobromination reaction. The selectivity of these methods towards the various microstructural units has been quantitatively examined from observation of the v(C~---C) stretching vibrations of the cis-l,4, trans-l,4 and vinyl-l,2 components in the polymer. The isolation and spectroscopic characterization of an intermediate formed during the hydrogenation of polybutadienes using tris(triphenylphosphine)rhodium0) chloride is also reported.

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Poly(p-phenylene vinylene) (PPV)-silica composite thin films were prepared via the sol-gel process incorporating a water-soluble PPV precursor. After solvent evaporation, the spin-coated or quiescently cast films were cured and the PPV precursor and the silica sol were completely converted into the PPV-silica composites. Quiescently cast films show an improved wave-guiding behaviour with a Z 3 value only slightly smaller than pure PPV films. Their structure consists of a nanophase-separated morphology composed of amorphous silica and paracrystalline PPV. Small-angle X-ray scattering and bright field transmission electron microscopy images indicate a random arrangement of the nanoscale domains with average domain size of approximately 4 nm. In contrast, spin-coated films show clusters and cluster-cluster aggregates approximately 100 nm in diameter. The clusters consist of particulate silica and pores, each about 3 nm in size, with the PPV contained in the pores and between the clusters. The observed morphologies are related to film preparation conditions in terms of sol-gel processing, taking the presence of the polymer into account.

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The miscibility of blends of poly(phenyl acrylate) (PPA) and poly(styrene-co-acrylonitrile) (SAN) of different copolymer compositions has been studied by a film clarity test, Tg and cloud-point (Tp) studies. It was revealed that the miscibility of solvent-cast blends varies greatly from solvent to solvent. Careful annealing of solvent-cast blends below the cloud temperature and above the Tg removed the solvent effect on the lower AN content side of the miscibility window. On the higher AN content side of the miscibility window the solvent effect could not be removed by annealing at the highest permissible temperature ( < Tp -~ 220°C). The phase diagrams of the blends were determined. The miscibility window at various temperatures has been constructed. It ranges between 11.5 and 32 wt% AN at 200°C. The various binary polymer segment interaction parameters have been evaluated using the composition of the miscibility window and the mean-field model.

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The deformation behaviour of thin films of poly(styrene-acrylonitrile) (SAN) and poly(styrene-acrylonitrile)/ poly(styrene-maleic anhydride) (SAN/SMA) blends was investigated at a range of different temperatures and strain rates. It is found that SAN shows a transition from shear yielding to disentanglement-induced crazing with rising temperature or decreasing strain rate. Addition of SMA leads, in the regime where SAN shows shear yielding, to more crazing and thus a more brittle behaviour. In the regime where SAN shows disentanglement crazing, addition of up to 50 wt% of SMA apparently leads to a rise in the monomeric friction coefficient in the blend, and therefore to a suppression of the disentanglement crazing mechanism. Still higher levels of SMA addition lead to pure crazing.

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The morphology and rheological behaviour of binary mixtures of poly(styrene-b-ethylene-co-butylenestyrene) (SEBS) block copolymer (Kraton G1651) and poly(2,6-dimethyl-l,4-phenylene ether) (PPE), prepared by melt blending using a twin-screw extruder, were investigated. It was found that the cylindrical microdomains of the PS phase in Kraton G1651 were changed into lamellar microdomains in a mixture containing 14.3 wt% PPE. However, when the amount of PPE in a mixture was greater than 28 wt%, we found that part of the PPE was solubilized into the PS block of the copolymer, and the rest underwent macrophase separation. For a Kraton G1651/PPE mixture containing 28.6 wt% PPE, the microdomain structure in a melt blended sample was different from that found in a sample prepared by solution casting followed by annealing, although macrophase-separated PPE regions were observed in both samples. This observation led us to conclude that the morphology of mixtures of block copolymers and homopolymers depended upon the sample preparation method. In addition, it was found that plots of the dynamic shear modulus versus the loss modulus for these mixtures was a very useful method of monitoring the morphological change in mixtures of block copolymers and homopolymers as a function of composition or temperature

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The effect of block copolymers on the interfacial tension tr was investigated for poly(ethylene oxide) (PEO)/poly(dimethylsiloxane) (PDMS) and for PDMS/polystyrene (PS). With PEO/PDMS the additives were the triblock copolymers PDMS-block-PEO-block-PDMS [P(DMS-EO-DMS)] and PEO-block- PDMS-block-PEO [P(EO-DMS-EO)]. For the former additive the number of monomeric units of the end blocks varied between 4 and 32 and that of the middle block between 23 and 77; these numbers are 70 and 52, respectively, for the latter. In the case of the system PS/PDMS, the diblock copolymer PS-block-PDMS [P(S-DMS)], consisting of 430 S and 68 DMS units, was studied. The effects turned out to be largest for the system PDMS/PEO/P(DMS-EO-DMS); it was therefore studied in greater detail within the temperature range of 70-150°C. Upon addition of increasing amounts of copolymer, tr falls rapidly to ~ 10% of its initial value and levels off as the critical micelle concentration (<0.5 wt% in the PEO phase at 100°C) is surpassed. Similarly, at a given concentration of the additive, tr approaches a limiting value as the number of monomeric units in the PDMS block is increased above 15. In contrast to the value of a of the pure blend, which is practically independent of temperature, that of the ternary system increases markedly with temperature. The results are compared with the predictions of Vilgis and Noolandi.

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The fatigue crack growth performance of injection moulded poly(aryl ether ether ketone) (PEEK) has been characterized using standard compact tension specimens and computer controlled photomicroscopy for crack length measurement. The influence of the materials parameters molecular weight and degree of crystallinity have been assessed together with experimental variables such as loading waveform shape and specimen orientation. Plots of crack growth rate against stress intensity factor range have been constructed from the experimental measurements. A quantitative measure of degree of crystallinity was obtained for each material using wide-angle X-ray diffraction. Post-fracture investigations using scanning electron microscopy were carried out to elucidate fatigue crack growth mechanisms. The results indicated that waveform shape had no effect on fatigue crack growth response. No anisotropic behaviour was evident, but an increase in molecular weight significantly improved the resistance of PEEK to fatigue crack growth. Similarly, increased crystallinity enhanced fatigue performance to a small extent. It is suggested that cyclic modes dominate fatigue crack growth at low rates of crack growth. However, with increasing speed, static processes begin to interact with cyclic mechanisms. At the onset of instability, failure is essentially dominated by static fracture modes.

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We experimentally examined the scaling relationship between correlation length ~ and polymer concentration c in homogeneous gels at swelling equilibrium. Polyacrylamide gels having various crosslink densities were synthesized and brought to swell in water/acetone mixtures with various mixing ratios. Their correlation lengths ~ were determined by small-angle X-ray scattering. A -3/4 power law (~ oc c-3/4) was found for the gels swollen in pure water, where c varied with the crosslink density as expressed by r in the as-prepared state. Here r denotes the ratio of the concentration of the monomer to that of the bifunctional monomer at the stage of specimen preparation. On the other hand, a -1/3 power law (~occ-1/3) was obtained for the gels having similar values oft when swollen in water/acetone mixtures with various mixing ratios. Both of the power laws are in accord with the predictions given by the c* theorem introduced by de Gennes for a homogeneous gel swollen in a good solvent.

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