1999 рік

A Monte Carlo simulation on a high coordination lattice employing the RIS scheme for short-range interaction and a Lennard–Jones potential for long-range interaction was carried out on C120 polyethylene thin film adsorbed at an impenetrable solid wall as well as freestanding films at 443 and 343 K, respectively. The interaction between the solid wall and polymer chains was given by a step-like function whose well depth is e . Three e values, ⫺6.0, ⫺2.0, and 0.0 kJ/mol, were tested in order to study the influence of the solid wall on the static and dynamic properties of the film. Significant density increase near the solid wall with the strongest interaction was observed, giving rise to the contraction of film thickness, which is in accordance with experimental observation. The presence of the solid wall reduces the interfacial width relative to the free-standing film and the extent of the reduction shows a tendency to grow with the strength of the interaction and lowering temperature. The population of chain end groups is significantly depressed near the attractive solid wall. The chain mobility as a whole in the normal direction toward the film surface is retarded near the free surface and the solid wall, while the bead mobility is dependent on the nature of interactions.

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New hydrophobically modified pullulans were synthesized in two ways: (i) neutral derivatives (HMPFs) obtained by direct esterification of pullulan with a perfluoroalkyl carboxylic acid (C8F17CH2CH2COOH), and (ii) ionic derivatives (HMCMPs) obtained by amidation of carboxymethylpullulan with two perfluoroalkylamines (C7F15CH2NH2 and C8F17CH2CH2NH2). The molar hydrophobe contents ranged from 1.1 to 4.8% with respect to the anhydroglucose units. Associative properties in aqueous solutions were studied by rheological and sizeexclusion chromatography/light-scattering measurements. In dilute solution, the polymers form intermolecular aggregates with a more compact conformation than that of precursors. In semi-dilute solution, the ionic derivatives are more viscosifying than neutral because of their better solubility. This effect is significant as the alkylperfluorinated chain length increases.

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The organic-inorganic hybrid interpenetrating network (IPN) composed of an epoxide-amine network and silica was prepared and studied. Formation of the inorganic phase from tetraethoxysilane (TEOS) by sol-gel process was characterized by 29Si n.m.r. spectroscopy, gas chromatography, small-angle X-ray scattering and electron microscopy. Kinetics of the silica structure build-up in the organic matrix, its final structure and morphology depend on the method of IPN hybrid preparation. The large compact silica aggregates, 100-300 nm in diameter, are formed during the one-stage polymerization. The two-stage process with the acid prehydrolysis of TEOS leads to an acceleration of gelation and formation of more open and smaller silica structures: 50-100 nm in diameter. The most homogeneous hybrid morphology with the smallest silica domains of size lo-20 nm, appears in the sequential IPN. The development of the silica structure is restricted by a rigid reaction medium of the preformed epoxide network

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Phase diagrams were determined for poly(vinylidene fluoride) (PVDF) and a terpolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene (VDF/HFP/TFE) in solutions composed of 1-octanol and dimethylformamide at 25°C. From the measured gelation and liquid–liquid phase separation data, binary interaction parameters were computed using a modified Flory–Huggins theory. PVDF microporous membranes were then prepared by isothermal immersion precipitation processes in various doping conditions. The formed membrane exhibited a particulate morphology characterized by a uniform package of spherical particles of identical size. These particles were identified to be full spherulites of PVDF using scanning electron microscopy, differential scanning calorimetry and small angle light scattering techniques.

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Modified poly(butylene terephthalate)–poly(tetramethylene glycol) multiblock copolymers were prepared by including either siloxane or silane units within the terephthalate hard blocks or the glycol soft blocks. These materials were characterized in terms of their dynamicmechanical properties, glass transition temperatures Tg, and morphology (as obtained from small-angle X-ray scattering measurements). One interesting result was the finding that putting siloxane units into the terephthalate hard blocks significantly decreased the storage modulus, whereas placing them into the glycol soft blocks somewhat increased it. Other interesting results were the observation that the Tg of the soft segments increased if the siloxane units were placed into the hard blocks but slightly decreased if they were placed into the soft blocks, while the hard-segment Tg was not observed at all. Some of these results could be explained in terms of the phase separation suggested by the X-ray scattering results.

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The effect of various compatibilizing compounds on the viscoelastic behaviour of semi-interpenetrating polymer networks (IPNs) based on cross-linked polyurethane and poly(n-butyl methacrylate) was investigated. It was established that in many cases, because of the specific chemical structure of compatibilizing compounds, the modified system reveals only one maximum of mechanical losses instead of two for initial semi-IPNs. This effect may be called compatibilization throughout the whole volume of the initially phase separated system. The disappearance of two maxima, revealing only one shows that the segregation degree in the IPN diminishes and in some cases miscible systems are formed.

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The structural relaxation process of poly(viny1 acetate) has been studied by differential scanning calorimetry. The sample was subjected to different thermal treatments including an isothermal annealing at temperature Ta for a time ta. The heat capacity cp(T) was measured during a heating scan. Thus, the experimental results consist of a series of cp(T) curves determined after thermal histories with different values of Ta and ta. The experimental results were compared with the prediction of a multiparameter phenomenological model described in references [15,16]. This model follows the evolution of the configurational entropy of the sample during the whole thermal history. The parameters of the model were calculated by simultaneous fits to five cp(T) curves, corresponding to different thermal histories (the parameters of the model have the character of material parameters, independent of the thermal history). This allows the determination of the temperature dependence of the relaxation times and the /3 parameter of the Kohlrausch-Williams-Watts equation. From these parameters and an estimate of the internal rotational barrier obtained by molecular mechanics calculations, the size of the smallest cooperative rearranging region in the Adam-Gibbs theory was calculated. This result is compared with the length of cooperativity calculated from the temperature fluctuation theory proposed by Donth

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The inverse gas chromatography (IGC) method was applied to poly(isobornyl methacrylate) (PIBORNMA) as a method for polymer characterisation and for the study of thermodynamic interactions. Six groups of solvents with different chemical natures and polarities were used to obtain information about PIBORNMA–solvent interactions. The PIBORNMA–solvent interaction parameters and the free energy of mixing were determined at a series of temperatures. The glass transition temperature (T g) of PIBORNMA was found to be about 105°C by differential scanning calorimetry. The thermodynamic sorption functions for the sorption process of probes of differing chemical nature into PIBORNMA solution were obtained and discussed in terms of the probes’ interactions with PIBORNMA. Furthermore, the contributions of –CH 2, –CyO, –CyO–OR, aromatic, cyclic ether and –OH functional groups in the six series of solvents to the sorption process were also obtained. Acetates, THF and ketones were found to be good solvents for PIBORNMA, whereas alkanes, aromatics and methanol were found to be non-solvents. Also the solubility parameter for PIBORNMA at infinite dilution was found by plotting the graph of [(d21 /RT) ¹ x⬁12 /V 1] versus solubility parameters, d 1, of some probes.

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Proton T2 relaxation and n.m.r. imaging experiments were utilized to study the molecular mobility and heterogeneity of cis-1,4-polyisoprene crosslinked with dicumyl peroxide in the presence of triallyl cyanurate (TAC) and zinc diacrylate (ZDA) as coagents. It was observed that the long T2 relaxation times of the rubber protons in peroxide/TAC or peroxide/ZDA crosslinked elastomers decrease with the increase in the crosslink density resulting from the addition of peroxide or coagent. The T2 relaxation times of protic solvent in swollen rubber are also affected by the physical property changes of the networks induced by peroxide and coagent addition. It was concluded that the solvent T2 relaxation times depend on solvent-polymer interactions as well as the crosslink density of the networks.

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The fracture of thin (3.18 mm) and thick (6.35 mm) specimens of polycarbonate (PC), acrylonitrile–butadiene–styrene (ABS) and PC/ ABS blends with both standard and sharp notches was examined by standard Izod and single edge notch three point bend (SEN3PB) instrumented Dynatup tests. Ligament lengths were varied for SEN3PB samples and the corresponding fracture data were represented by plotting the specific fracture energy (U/A) as a function of ligament length ('). The slope of these plots was found to be closely related to both the Izod impact strength and the size of the process (or stress whitened) zones surrounding the crack surface. Significant morphology coarsening was seen in some PC/ABS (70/30) blends for thick (6.35 mm) injection molded parts; blends compatibilized with 1% of an SANamine polymer exhibited well-dispersed, stable morphologies. The effects of blend composition, ABS type, sample geometry, PC molecular weight, temperature, rubber concentration and reactive compatibilization on the fracture properties of these materials were examined.

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