1999 рік

An acrylic-modified polyolefin type ionomer (Ion., Zn 2⫹), was successfully applied to compatibilize poly(ethylene terephthalate) (PET)/ polyamide-6 (PA-6) blends. Melt-mixed blends were prepared at various PET/PA-6 ratios and at constant main component ratio, with various amounts of Ion., Zn 2⫹. The techniques applied to characterize compatibilization were tensile testing, dynamic mechanical analysis, d.s.c. and morphology of cryofractured and etched specimens using electron microscopy (SEM). The effects of thermal history and physical ageing were also examined. Compatibilization was attained at Ion., Zn 2⫹ levels higher than 10 wt%. Good tensile and impact properties were obtained in quenched blends, while in annealed samples crystallization of main components reduced ductility drastically.

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A high-temperature non-aqueous dispersion polymerisation (NAD) route to poly(4-oxybenzoate-co-4-phenylene isophthalate) liquid crystal polymers (LCP) is described. Stable dispersions were obtained in the presence of organo-clay stabilisers. The use of organo-clay stabilisers is discussed and the advantages of the NAD route are contrasted with traditional melt polycondensation routes.

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The curing reaction of the system diglycidyl ether of bisphenol A (DGEBA) with different amine concentrations (TETA) has been studied by means of thermal scanning rheometer (TSR) and dynamic mechanical thermal analyser (DMTA). The aim of this work was focused on studying the effect of the amine concentration on the kinetic, the rheologic characteristics during the crosslinking process, and the dynamicmechanical properties of the system. Through TSR measurements, the gel time was observed to vary with amine concentration and cure temperature when measurements were carried out under isothermal conditions. The gel time also was found to depend on the heating rate when the measurements were done varying the temperature. The apparent activation energy (Eu) of each system was calculated from two different methods; the gel time (rg) and the complex viscosity (n*) measurements, respectively. The study of the dynamic-mechanical properties of the resins such as epoxy by means of the three-point bending mode in DMTA, gives information of their viscoelastic properties allowing the calculation of the glass transition temperature (Tg) and the apparent activation energy of the relaxation process (Ea*)

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We observed, via transmission electron microscopy, the evolution of a dispersed morphology from a modulated co-continuous morphology in immiscible blends of two amorphous polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS). Upon rapid precipitation of a homogeneous solution, which can be regarded as being equivalent to spinodal decomposition via temperature quenching, we observed a modulated co-continuous morphology for all three blend compositions, 70/30, 50/50, and 30/70 PMMA/PS blends. This observation is interpreted with the Cahn’s linearized theory, which has been found to be accurate in describing phase separation in the early stage of spinodal decomposition. When a rapidly precipitated PMMA/PS blend specimen having asymmetric (70/30, 60/40, 55/45 or 30/70) blend composition was annealed under isothermal conditions at 170°C for varying periods, the modulated co-continuous morphology evolved into a dispersed morphology, in which the major component formed the continuous phase and the minor component formed the discrete phase, and into a 'dual mode’ of dispersed morphology in the symmetric (50/50) PMMA/PS blend. This observation is interpreted in terms of the percolation-to-cluster transition mechanism proposed by Hashimoto and co-workers. The morphology evolution, during isothermal annealing, of a rapidly precipitated blend may be regarded as being equivalent to late stages of spinodal decomposition, which is controlled by diffusion and coalescence. The rate of morphology development in PMMA/PS blend during isothermal annealing was found to depend on the zero-shear viscosity ratio of the constituent components. This observation is interpreted in terms of Siggia’s theory for late stages of spinodal decomposition.

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Poly(ether-urethanes) based on 4,4 0 -methylene bis (4-phenylisocyanate) or toluene diisocyanate and poly(tetramethylene oxide) have been synthesised varying the molecular weight of the soft segment. The hard/soft segment mixing has been studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. The polymers have been exposed to UV radiation, and the changes in the chemical structure have been analysed by FTir spectroscopy. The extent of the photodegradation in the urethane linkage increases with soft segment molecular weight. The phase separated structure is a critical factor which must be taken into account in order to study the photodegradation of the hard segments in poly(ether-urethanes).

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Copolymer membranes composed of chloromethylstyrene and divinylbenzene were reacted with 4-vinylpyridine and then trimethylamine to prepare highly tight anion exchange membranes. When 4-vinylpyridine reacted with chloromethyl groups of the copolymer membranes, 4vinylpyridine polymerized in the membrane matrix to form a ladder-like polymer, of which one polymer was cross-linked. Consequently, relationships of ion exchange capacity and water content to electrical resistance of the obtained membranes were completely different from those of the anion exchange membranes with benzyl trimethylammonium groups cross-linked with divinylbenzene. With increasing reaction time of the copolymer membranes with 4-vinylpyridine, the electrical resistance of the membranes markedly increased with a small decrease in ion exchange capacity and with the decrease in water content. And fixed ion concentration of the membranes reacted with 4-vinylpyridine and then trimethylamine was higher than that of the membranes with benzyl trimethylammonium groups. These are thought to be because of the formation of a ladder-like polymer in the membrane matrix and the introduction of pyridine unit, which is more hydrophobic and bulkier than trimethylamine. The remarkable decrease in the pore size of the membranes was confirmed by the measurement of the diffusion coefficient of neutral molecules, urea and glucose, through the membranes.

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The phenomenological and structural aspects of biaxial drawing of a vinyl alcohol-rich ethylene/vinyl-alcohol copolymer is studied as a function of temperature. For draw temperature above the crystalline mechanical relaxation, T,, sharp necks accompanied with catastrophic fissures develop during simultaneous biaxial drawing as well as in the first step of sequential biaxial drawing. For draw temperature below T,, simultaneous biaxial drawing can be successfully achieved via propagation of diffuse necking so that a minimum macroscopic draw ratio of about 3 X 3 is required to obtain a uniform plastic strain. The strong interaction anisotropy of the sheet-like structure of the monoclinic phase is responsible for the fissuring trend at T > T,. In contrast, the isotropic mesomorphic phase that is strain-induced at T < T, enables simultaneous biaxial drawing. The development of a planar texture suggests that the transformation results from transverse crystal slip. However, the random distribution of the H-bonds in the mesomorphic phase is rather consistent with an accumulation process of conformational defects that remain frozen in the crystal

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Dendrimers are a new class of three-dimensional, man-made molecules produced by an unusual synthetic route which incorporates repetitive branching sequences to create a unique novel architecture. Exceptional features of the dendritic architecture include a high degree of structural symmetry, a density gradient displaying an intra-molecular minimum value and a well defined number of terminal groups which may be chemically different from the interior. The combination of these features creates an environment within the dendrimer molecule which facilitates trapping of guest species. Recently, dendritic polymers have been used as soluble templates/unimolecular reactors from which nano-clusters of inorganic compounds or elements can be synthesized. The basic concept involves using dendrimers as hosts to preorganize small molecules or metal ions, followed by a simple in situ reaction which will immobilize and stabilize domains of atomic or molecular guest components (inorganic compounds as well as elemental metals). In one of these examples poly(amidoamine) (PAMAM) dendrimers have been used, to attract copper(II) ions inside the macromolecules where they are subsequently reacted with solubilized H 2S to form metal sulfides. These organic/inorganic, dendrimer-based hybrid species have been termed 'nanocomposites’ and display unusual properties. For example, solubility of the nanocomposites is determined by the properties of the host dendrimer molecules. This allows for solubilization of the inorganic guest compounds in environments in which they are inherently insoluble. Since it has been established that there is no covalent bond between host and guest, these observations suggest that the inorganics are physically and spatially restricted by the dendrimer shell. However, this structure has not been verified. In this investigation a preliminary understanding of the physical structure of these dendrimer-based nanocomposites was sought. A model system of PAMAM dendrimer–copper sulfide nanocomposites was studied in various stages of its formation using a combination of small angle X-ray and neutron scattering experiments. The results suggest that little perturbation of the dendritic species occurs on complexation, but indicate that a secondary super-molecular aggregation phenomena occurs within nanocomposite solutions.

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Poly(amide–imide)/TiO2 (PAI/TiO2) composite films were prepared by an in situ sol–gel process. These composite films exhibited high optical transparency, having nanosized TiO2 rich domains well dispersed within the PAI matrix. The size of the domains increased from 5 to 50 nm when the TiO2 content was increased from 3.7 to 17.9% by weight. Hydrogen bonding interactions between the amide groups in the PAI and the hydroxyl groups on the inorganic oxide were observed. In comparison to the pure PAI polymer, the PAI/TiO2 composite films exhibited higher glass transition temperature, an increase and flattening of the rubbery plateau modulus, and a decrease in crystallinity.

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The thermodynamic fusion theory of strength of perfect polymer fibers of finite molecular weight is extended to include imperfect (i.e. real) fibers of incomplete crystallinity and orientation. Approximate equations for failure strength, strain, and work of failure are derived by extracting from the real visco-elastic fiber an equivalent reversible component suitable for thermodynamic analysis. This is facilitated by an explicit relationship between fiber breaking stress, σ* , and breaking strain, ε* , which is shown to be σ* ˆ 0:632Kε* (K ˆ modulus) for constant strain-rate deformations. It is shown that fiber breaking time is equivalent to the fiber visco-elastic mechanical relaxation time. Experimental data shows that the activation energy of rupture of polyethylene fibers is not the activation energy of covalent bond rupture. Instead it agrees with the activation energy expected of crystal melting in accordance with the fusion theory of rupture. The activation volume of the polyethylene fibers also agrees with the value expected from this theory.

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