1999 рік

The mechanisms controlling the elution of carboxylated polyurethanes (CPUs) and polyurethane ionomers (PUIs) during the size exclusion chromatography (SEC) separation process in tetrahydrofuran (THF) were investigated. In order to elucidate the elution process, their dilute solution viscosity behaviour was studied as well. Sample molar mass averages were determined by SEC using polystyrene calibration (SEC-PS) and in the case of CPUs also by SEC coupled with a multi-angle light scattering detector (SEC-MALS). The molar mass averages and intrinsic viscosities of CPUs decrease with increasing degree of carboxylation as a consequence of side-reactions. The large difference in reduced viscosity between non-carboxylated PU and CPUs can be attributed to different macromolecular conformations in THF solution. The molar mass averages of PUIs determined by SEC-PS were much lower than those of the parent CPU and showed a slight dependence on the type of counterion used. In the selected series, the molar mass averages and intrinsic viscosities increased in the order Ca 2þ < Li þ < Na þ < K þ. The addition of CF 3COONa had no influence on the solution viscosity of CPUs, while it prevented the association of PUIs.

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Atomistic molecular modelling has been utilized to construct a proton-conducting polymer electrolyte system consisting of poly(ethylene oxide) sulfonic acid anion (PEO sulfonic acid anion), water, hydronium ion and proton in an amorphous cell. The forcefield was parametrized to simulate proton transport as accurately as possible in an atomistic model. The coordination study was made and found to be mainly in accordance with experimental data. The diffusion coefficients for the PEO sulfonic acid anion, water, the proton and for the hydronium ion were determined. The ion conductivities of the whole system and of the ions were estimated and found to be in accordance with experimental values. The good correlation between the experimental and simulated results shows that the used model may provide guidance for evaluating new materials by experimentalists.

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Phenomena displaying the behaviour expected when molecular species segregated at the growth front lower the supercooling for continued growth have been observed using linear low-density polyethylene (LLDPE) nucleated on a fibre to form a macroscopic row structure. Initially, a close-packed array of lamellae grows epitaxially from the fibre, with the lamellae too close together for other parallel lamellae to form between them, so that rejected species can only accumulate ahead of the growth envelope. The more-branched molecular sequences rejected in this polymer lower the equilibrium melting temperature and with it the isothermal supercooling. In consequence, the texture coarsens and lamellae become thicker, both for the rows and in adjacent spherulites. During this process the isothermal growth rate declines continuously as the impurity layer develops, but spherulites always grow faster than rows because their more open crystal-melt interfaces give lower concentrations of impurities. The habit of the rows is then prone to change abruptly as spherulitic growth nucleates sporadically at points around the instantaneous growth envelope and grows faster than, and hence ahead of, the remainder of the row. The depth to instability and the average distance between spherulitic nuclei both increase with crystallization temperature but the former only slightly. It is suggested that nucleation occurs where fluctuations have reduced the concentration of segregated species and we found that the internuclear distance scales approximately as the inverse one-third power of the growth rate. No such instability or cellulation is found for spherulites growing adjacent to the rows even though their characteristic microstructure develops from the start, thereby confirming in a particularly clear way that morphological instability is not the cause of spherulitic growth in polymers.

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The effect of the poly(acrylic acid) homopolymer [PAA] existing in poly(propylene-graft-acrylic acid) [PP-g-AA] on the morphology and rheological properties of a PP-g-AA and polystyrene [PS] blend with varying amounts of poly(styrene-ran-glycidyl methacrylate) [PSGMA] was investigated. Two different PP-g-AAs, one with PAA, [PP-g-AA(O)] and the other without PAA, [PP-g-AA(T)], were used. We have shown that when the amount of PS-GMA is increased, the dispersed domain size of PP-g-AA(O) in the PP-g-AA(O)/PS blend does not decrease, even when the amount of PS-GMA in the blend is as large as 25 wt%. Conversely, the dispersed domain size of PP-g-AA(T) in the PP-g-AA(T)/PS blend does decrease gradually and reaches a steady value. However, the reduction in the dispersed domain size (D r) for PP-gAA(T) in the PP-g-AA (T)/PS blend with PS-GMA was just 30%. Here, D r is defined by the dispersed domain size of the blend without PSGMA minus that with 15 wt% of PS-GMA divided by the former. The changes in rheological properties with the proportion of PS-GMA content in the PP-g-AA(T)/PS blend were different to those for the PP-g-AA(O)/PS blend, thus demonstrating that the presence of PAA significantly affects the rheological as well as the morphological blend properties.

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A hot-air (HA) drawing method has been applied to poly(ethylene-2,6-naphthalate) (PEN) fibers in order to improve their mechanical properties. The HA drawing was carried out by blowing hot-air controlled at a constant temperature against an original PEN fiber connected to a weight. As the hot-air blew against the fiber at a flow rate of 90 l/min, the fiber elongated instantaneously at a strain rate in the range from 15.9 to 25.2 s 21. The strain rate during the HA drawing increased with increasing drawing temperature and applied tension. When the HA drawing was carried out at a drawing temperature of 2508C under an applied tension of 17.4 MPa, the strain rate had the highest value of 25.2 s 21. Draw ratio, birefringence, crystallite orientation factor, and mechanical properties increased as the strain rate increased. The fiber drawn at the highest strain rate had a birefringence of 0.436, degree of crystallinity of 45%, tensile modulus of 29 GPa, and dynamic storage modulus of 30 GPa at 258C. The mechanical properties of the fiber obtained had almost the same values as those of zone-annealed PEN fibers.

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The synthesis of a new series of aromatic bis(ether acid)s and bis(ether acid chloride)s by fluorodisplacement with catechol or its derivatives has been developed and exemplified. These monomers allow the synthesis of new aramids (poly(ether amide)s), polyarylates (poly(ether ester)s) and copolyarylates in which o&o-phenylene units are enchained through ether linkages. These polymers are signifi- cantly more flexible and, therefore, more soluble than conventional aromatic polyamides and polyesters. They have useful levels of thermal stability, associated with relatively high glass-transition temperatures ( > 2OO”Q are processable from solution or the melt, and are potentially crystallizable. Liquid crystalline poly(ether ester)s were prepared. Polyamides prepared from bis(ether acid)s in which all three aromatic rings, separated by ether linkages, are all ortho-substituted gave low-molecular weight polymers.

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Melt rheology, phase morphology and properties of (60/40) isotactic polypropylene/ethylene-co-propylene (iPP/EPR) blends containing EPR copolymer synthesized by means of a titanium based catalyst with very high stereospecific activity (EPR Ti) were compared to that of (60/40) iPP/EPR blends containing EPR copolymer synthesized by using a traditional vanadium based catalyst (EPR V). It was found that both the melts are to be classified 'negative deviation blends’ and that for such a composition the copolymer represents the dispersed phase. SEM investigations showed in fact that the EPR phase segregate in to irregular shaped domains localized in the core of the bars, the dispersion coarseness increasing with an increase in the ratio between the EPR viscosity and iPP viscosity. At low temperatures the iPP impact strength was improved, comparatively better properties being shown by the blends containing the EPR V copolymer. The different behaviour of EPR Ti and EPR V phases as impact modifiers was ascribed to their both different dispersion degree and microstructure. For test temperatures higher than EPR T g the ethylenic crystallinity exhibited by the EPR Ti phase was considered to induce toughening deterioration by decreasing tie molecules density in the EPR Ti domains, notwithstanding the beneficial effect of the ethylenic build-up. The reduction in iPP crystallinity index (X c) value found for iPP/EPR Ti blends indicated a strong interference of the crystallization process of EPR Ti ethylenic sequences with the iPP crystallization process. SAXS investigations revealed in addition that the iPP/EPR Ti materials are characterized by an amorphous interlamellar layer (L a) higher than that shown by plain iPP and iPP phase crystallized in presence of EPR V copolymer. Taking also into account results obtained studying blends containing lower content of such EPR phases composition effects were investigated. WAXS studies showed that with increasing copolymer content the ratio between the apparent crystal size of iPP phase grown in a direction perpendicular to the (110) crystallographic plane [D (110)] and that grown in direction perpendicular to the (040) crystallographic plane [D (040)] increases. Such an effect was related to an increased iPP nucleation density according to DSC results.

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Processing of a SMA/PMMA blend through a capillary results in a complex change of phase behaviour with deformation rate. Both deformation induced demixing and remixing are observed. This complex phase behaviour as a function of apparent shear rate, is in qualitative agreement with experimental and theoretical results found for a polystyrene/poly vinyl methyl ether (PS/PVME) blend (Fernandez ML, Higgins JS, Horst R, Wolf BA. J. Polym. Sci. Polym. Lett. 1995;36(1)). In addition a different tongue shaped area of partially demixed material is observed in the current work (type b). This sample appearance is proposed to be related to the occurrence of vortices near the entrance of the capillary. This is a phenomenon which only occurs in contraction flow experiments. Pure shear rheological experiments, such as parallel plate or cone and plate, will not show such behaviour. The deformation induced demixing is spinodal phase separation. This is concluded from light microscopy experiments and via reheating experiments, showing that the blend needed only 15–25 s to remix. Preliminary results suggest that in addition to shear, elongation can cause dramatic changes in the blend phase behaviour. Capillary experiments are difficult to interpret because of the combination of shear, elongation, pressure and viscous heating. However, industrial scale blend processing such as injection moulding shows similar complexity. Hence capillary measurements are the best comparable small scale experiment. Future experiments will focus on modifying the capillary geometry, in order to discriminate between the influence of shear and elongation.

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The effect of short polyethylene terephthalate (PET) and nylon 66 (PA) fibres, and their chemical treatment with an azide derivative, on the PP crystallization kinetics and thermodynamics has been investigated. Both fibres are effective nucleant agents for polypropylene (PP) crystallization, giving rise to the phenomenon of PP transcrystallinity on their surface. However, the presence of azide groups on the chemical structure of the fibres produces a different effect on the PP crystallization kinetics. Azide-modified PET fibres give rise to an additional increase of the global rate of the PP crystallization process, but in this case the transcrystalline development of the PP is not so sensible as in the presence of the unmodified fibres. An opposite behaviour is observed with the azide-modified PA fibres. In general, it can be established for the studied composites that the spherulitic development of the polymer matrix comes from an instantaneous and athermal nucleation whose growth is not constant. It is also suggested that transcrystallinity and a good adhesion at the interface may take place independently one of each other.

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Poly(vinyl alcohol) (PVA) was esterified with 10-undecenoyl chloride to give polymers with different degrees of modification which were studied in order to find how the concentration of reactive sites can influence the crosslinking process. The polymers obtained were characterized by spectroscopic techniques, elemental analysis and thermal methods. Weight average molecular weights and viscosities were determined. Thermal crosslinking of the double bonds on the side chain took place in all cases, but was overlapped by the degradation process. Thus, dicumyl peroxide had to be used to obtain the cured material and avoid degradation. Activation energies for radical initiated crosslinking were determined by means of dynamic DSC studies. Isoconversional kinetic analysis was applied to DSC data and the dependences of activation energies on conversion degrees were obtained and compared with those obtained from polymers with the same pendant chain but a more flexible polyether main chain.

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