1993 рік

The two series of polyether polyurethane anionomers discussed in part I, undergo emulsification on addition of water to solutions in methyl ethyl ketone. The phase inversion mechanism depends on the structure of the counterion, ionic content and dispersion temperature. The dispersion process can be divided into three stages: separation of hard segment aggregates due to adsorption of water on their surface, water entering into more disordered and then less disordered hard domains, and finally a rearrangement of agglomerates to form microspheres. Films cast from emulsions have crystallizable soft domains, as do films cast directly from solutions. The dispersion can cause a disruption of the packing arrangement in the hard domains, leading to an increased phase separation for the TEA system and an increased phase mixing for the EDEA system. Films cast from solutions have hard domains dispersed in the continuous phase of soft domains. After dispersion, the hard segments originally distributed in the dispersed phase can be inverted to become a hard domain network or a continuous phase.

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Various functions describing the anisotropy of segmental dynamics such as mean mobility-amplitude term, orientation-mobility correlation, directivity and sense of mobility are determined for chains with different degrees of extension using the results from Brownian dynamics simulation. Strong dependence of these properties on chain deformation is observed

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A new imide-containing phthalonitrile resin has been synthesized and studied by thermal analysis. The initially formed di(amic acid) phthalonitrile intermediate, which was synthesized from reaction of 4-(3-aminophenoxy)phthalonitrile with 3,3',4,4'-benzophenonetetracarboxylic dianhydride, is readily converted into the imide linkages before commencing with the polymerization reaction. The monomer was polymerized in the presence of a minute quantity of 1,3-bis(3-aminophenoxy)benzene by an addition polymerization reaction. Thermal properties were determined by differential scanning calorimetry and thermogravimetric analysis.

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Rolled high density polyethylene with various molecular weights was used to study the effect of primary structure on the properties of the material. Keeping the molecular weight distribution at 2, and with similar processing conditions, it was found that the structure, morphology and anisotropic mechanical behaviour depended strongly on the molecular weight. The low molecular weight samples possessed high modulus and yield stress in the roll direction and showed brittle fracture in the direction perpendicular to the roll direction. The high molecular weight samples showed high modulus and yield stress in the direction perpendicular to the roll direction. The morphology of the internal surface showed a transitional change from fibrillar structure for low molecular weight samples to a smooth surface for high molecular weight samples. Wide angle X-ray diffraction revealed that, for samples with high molecular weight, the crystallographic axes were selectively correlated with the coordinate axes used in defining the samples. Small angle X-ray scattering showed four-point patterns for high molecular weight samples. It is suggested that samples with high molecular weight possess more entanglements among the tie chains connecting the lamella blocks. This results in higher orientation of the three crystallographic axes, a, b and c, along the thickness, transverse and roll directions of the sample, respectively. Entanglement also reduces the anisotropic behaviour in the roll-transverse plane

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A single specimen J-integral method has been used to evaluate the critical energy for crack initiation in rubber-toughened poly(methyi methacrylate). An abrupt transition is observed in the evolution of J~c as a function of particle volume fraction and the sudden increase in toughness appears to be directly related to a comparable change in the materials's ability to nucleate plasticity.

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Poly(vinyl alcohol) (PVA) films prepared by gelation/crystallization from dimethyl sulphoxide/water solutions were drawn in an oven at 125°C under nitrogen. Two PVA samples with degrees of polymerization of 2000 and 4400 were used. The drawability was affected by the composition of the solvent mixture as well as by the quenching temperature. This interesting phenomenon is discussed in terms of the morphology of the gels and dried films, as studied by crystallinity, wide-angle X-ray diffraction, birefringence and small-angle light scattering under Hv polarization. Thus, it turned out that crystallinity plays an important role in assuring facile drawability, while the solution concentration and the degree of polymerization have little effect on the drawability. The maximum draw ratio could be achieved only for specimens with the lowest crystallinity. This indicates that the deformation mechanism of PVA gel films is quite different from those of polyethylene and polypropylene gel films.

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In a previous paper, the effect of molecular weight on the structure, morphology and anisotropic behaviour of high density polyethylene (HDPE) has been studied. Entanglements among tie chains connecting the lamella blocks were believed to be the factor that initiated the intrinsic differences. A further study of the fracture behaviour was carried out. It was found that samples with low molecular weight showed brittle fracture with only a small amount of fracture energy being consumed. For high molecular weight samples, a large plastic deformation was associated with the crack extension. The energy consumed for crack extension was almost proportional to the molecular weight. Further stretching of the samples after rolling resulted in a different fracture mechanism and samples showing ductile fracture changed into brittle failure. The morphology of the fracture surface was also studied. It was found that two types of fracture surface existed even for samples with brittle fracture. The fractography was strongly related to the fracture energy. The fracture surface of the ductile failure type samples showed a fibrillar structure. It is suggested that peeling the plastically deformed part off the undeformed surface was the fracture mechanism for the high molecular weight samples. The fracture energy of HDPE without the effect of entanglement was obtained by extrapolating the fracture energy down to zero molecular weight to yield a value of ,-, 370 J m-2

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Plasma polymers (PPs) have been prepared from methacrylate precursors and analysed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (X.p.s.). The negative SIMS data for plasma polymerized methyl methacrylate (ppMMA) were compared with that of a low molecular weight oligomer and a high molecular weight conventional poly(methyl methacrylate). This facilitated the interpretation of the SIMS data and has enabled a qualitative structure for ppMMA to be proposed. The secondary ion mass spectra from PPs of ethyl methacrylate and butyl methacrylate are shown to be very similar to ppMMA, where the methyl group is replaced by an ethyl and a butyl group, respectively. The X.p.s. data for ppMMA showed that the PP had retained ~ 80% of the oxygen from the monomer. Much of this was present as the ester group which indicates that extensive fragmentation of the monomer had not occurred during plasma polymerization. Evidence that the monomer structure had been retained in the PP was also provided by the SIMS data; a number of negative ions (e.g. at m/z = 85, 87, 101 and 187) have structures which contain a complete monomer unit.

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A range of simultaneous fully interpenetrating polymer networks (IPNs) based on polyurethane (PU) and poly(methyl methacrylate) (PMMA) were prepared and evaluated using dynamic mechanical analysis. The tests were conducted at resonance frequencies over a wide temperature range. The IPNs produced broad glass transitions, with a unique tan 6 peak of rectangular waveform occurring at approximately 70/30 by weight PU/PMMA composition. Tan ~ broadening was explained in terms of the patterns of behaviour of the dynamic loss and real moduli during the transition. The type of tan 6 broadening was not experienced in PU by crosslinking variation alone. Multiplexed dynamic mechanical runs for the time-temperature superposition were conducted at various frequencies. The Williams-Landel-Ferry (WLF) equation fitted the experimental shift factors over the wide transition regions. The resultant WLF coefficients indicated the presence of larger-than-expected free volumes in the PU-dominated IPN compositions, which, in turn, precipitated glass transitions

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The crystallization from the melt, the morphology and the miscibility of syndiotactic polystyrene/poly(vinyl methyl ether) (SPS/PVME) blends and syndiotactic polystyrene/poly(2,6-dimethyl-l,4-diphenylene oxide) (SPS/PPO) blends have been analysed by differential scanning calorimetry and optical microscopy. It was found that the kinetic parameters are strongly altered by the blending and by the crystallization conditions. In particular, the spherulite growth rate of SPS decreases if PPO is added, whereas it increases in the case of SPS/PVME blends. The half-time of crystallization is drastically increased by the presence of both PPO and PVME. The PVME segregated into spherical domains in the SPS intraspherulitic region, whereas there is no microscopic evidence that the PPO forms segregated domains. These results were correlated to the viscosity of the melt and the degree of miscibility of the blends. It was concluded that the SPS/PPO system is completely miscible in the amorphous phase, whereas PVME forms with SPS a two-phase separated system. This conclusion results in agreement with the presence of one Tg, composition-dependent, for the SPS/PPO blend, and of two Tg for the SPS/PVME blends.

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