1999 рік

High-temperature infrared spectroscopy to 1808C identifies irreversible chemical changes that occur in solid state complexes of 1,2polybutadiene and palladium chloride, prior to the onset of oxidation. The decrease in infrared absorption intensities at 910, 994, 1418 and 1640 cm 21 signifies the consumption of carbon–carbon double bonds in the polymer whose microstructure is 80% 1,2-vinyl. The loss of CyC functionality in the sidegroup at elevated temperatures can be explained by palladium-catalyzed dimerization reactions. Transient experiments between 1008C and 1408C reveal that the reduction in the CyC infrared signal at 1640 cm 21 follows an approximate 1st-order rate law which is consistent with a previous calorimetric study of exothermic kinetics over the same temperature range. Characteristic nthorder chemical reaction time constants for solid films of 1,2-polybutadiene with 4 mol% palladium chloride have been calculated at 1008C, 1258C and 1408C via infrared spectroscopy. These reaction time constants decrease at higher temperature with an apparent Arrhenius activation energy of < 43 kJ/mol. Palladium complexes with cis-polybutadiene reveal that p back-donation of electron density from the metal center into the antibonding orbitals of the alkene group in the main chain shifts the CyC absorption from 1653 to 1543 cm 21. The uncomplexed signal at 1653 cm 21 is insensitive to high-temperature annealing whereas the palladium-p -complexed signal at 1543 cm 21 is severely attenuated after annealing for a few minutes at 1508C. This suggests that the formation of a p -complex is required before hightemperature irreversible chemical reactions. Infrared-determined characteristic nth-order chemical reaction time constants for solid films of cis-polybutadiene with 4 mol% palladium chloride at 1008C, 1258C and 1408C are five-fold longer than the corresponding reaction time constants for 1,2-polybutadiene with 4 mol% PdCl2. This kinetic mismatch is consistent with the trend in reaction rates for mono-substituted vs. di-substituted small-molecule alkenes, and suggests that a mixing strategy is required to compatibilize 1,2-polybutadiene and cispolybutadiene via PdCl2 at high temperatures.

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The yielding and plastic behaviour of atactic poly(oxypropylene) (a-POP) was simulated under the uniaxial compression condition using atomistic modelling, and compared with the result under the uniaxial extension condition. Typical stress–strain curves showing yielding and plastic behaviour were obtained under the uniaxial compression condition. It was observed that the stress under uniaxial compression is greater than that under uniaxial extension. This observation suggests that the difference of stress level between the two conditions is not related intrinsically to the structural defects in the sample. When the energetic state of a-POP was analysed by monitoring the change of energy component with strain, it revealed that the change of total energy with strain was governed dominantly by non-bonded interaction, such as van der Waals and Coulombic interaction. The role of Coulombic interaction is more important under compression than under extension.

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Solid structures of the compositionally fractionated bacterial poly(3-hydroxybutyric acid-co-3-hydroxypropionic acid)s [P(3HB-co3HP)], bearing much narrower comonomer compositional distributions, were studied by high-resolution solid-state 13C n.m.r. 1H– 13C H ) of chain-carbon nuclei was found to strongly depend on the micro-environments cross-polarization relaxation behaviour (T CH and T 1r they were involved in, and the resonance contributions pertaining to different phases were therefore distinguished. Employing CP/MAS and PST/MAS methods, 13C resonance signals from the crystalline and non-crystalline regions were selectively enhanced. The observed chemical shifts demonstrated that co-crystallization did not occur in the P(3HB-co-3HP) system. Spin-lattice relaxation times (T 1C) of carbon nuclei attributed to 3HB and 3HP units were found to be considerably different, reflecting their distinguishable difference in local segmental dynamics. From the lineshape analyses of 3HB methyl carbon resonance measured by a DD/MAS method, it was revealed that the presence of minor 3HP comonomer units significantly suppressed the crystallization of a 3HB-rich semicrystalline copolyester. In addition, a correlation was found between average block length of 3HB sequences estimated by solution-state 13C n.m.r. spectra and crystallizability of semi-crystalline copolyesters.

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By curing of in water dispersed droplets of an aromatic or aliphatic epoxy resin, respectively, glassy or rubbery thermosetting epoxy spheres can be prepared in a relatively easy way. The rubbery epoxy particles can successfully be applied as a toughening agent for glassy epoxy matrices. The advantage of these preformed modifiers is the control over the final morphology as the size and concentration of the dispersed rubber phase can be chosen independently. The improvement in fracture toughness and the morphological features of the fracture surfaces are identical to standard, but also more complex, toughening routes, such as the application of liquid rubbers [Sultan JN, Laible RC, McGarry FJ. Appl. Polym. Symp. 1971;16:127; Sultan JN, McGarry FJ. Polym. Eng. Sci. 1973;13:29]. The use of this new class of rubber modifiers is not restricted to glassy epoxy resins, but may also be applied to produce impact-modified thermoplastics with a predetermined particle size and rubber content.

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The interfacial thickness between immiscible polymers, bisphenol A polycarbonate (PC) and styrene–acrylonitrile random copolymers (SAN), was measured by ellipsometry as a function of temperature and acrylonitrile content in SAN, in order to study the miscibility between PC and SAN. Both the temperature and copolymer composition (AN content) dependence of the interfacial thickness in the equilibrium state indicated a maximum. Using the values of the interfacial thickness, it is possible to calculate the polymer–polymer interaction parameter x AB between PC and SAN. The x AB exhibited the lowest positive value at about 200°C for each copolymer composition due to the maximum of the interfacial thickness, i.e. at low temperature range, x AB decreased with increasing temperature, then x AB increased at high temperature range. This behaviour implies the possibility of the coexistent behaviour of upper and lower critical solution temperature (UCST and LCST) in the phase diagram of the mixture consisting of polymers with suitable molecular weight. This coexistent behaviour of UCST and LCST was confirmed by measuring cloud point curves of the mixtures having lower molecular weight PC. On the other hand, the copolymer composition dependence of x AB also has a minimum in a certain copolymer composition, which leads to the miscibility window behaviour. From these results, it was shown that there appeared to be a loop-type miscibility window ('miscibility egg’) in the miscibility diagram of copolymer composition versus temperature of PC/SAN. From the calculation based on these results, it has also been shown that all three segmental interaction parameters x i/j of PC/SAN, i.e. x S/C, x AN/C and x S/AN, decreased with increasing temperature monotonically. It was predicted that the LCST behaviour in PC/SAN mixtures could occur due to the remarkable decrease of interaction x S/AN between comonomers in SAN at high temperature, without the free volume contribution.

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The phase-separated structure and molecular mobility for core-shell type polymer particles composed of poly(butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) have been examined by high-resolution solid-state 13 C n.m.r. spectroscopy. These types of polymer particles were prepared by the two-step emulsion polymerization of BA and MMA in the presence or absence of ally methacrylate (AMA) as a crosslinking agent. The analysis of the 1 H– 13C cross polarization process has revealed that molecular mobility of the main-chain of PBA is significantly restricted for sample BA2M prepared in the presence of 1.6 wt% AMA. 1 H spin–lattice relaxation time measurements in the rotating frame have also revealed that the PBA and PMMA phases are phase-separated in a scale of several nm for the polymer particles. Furthermore, the 1 H spin diffusion process, measured by the combined pulse sequence of the Goldman–Shen pulse sequence and the CP process, has been successfully analyzed in terms of the equation derived by the simple two-spin cross relaxation theory. The time constant TSD for the 1 H spin diffusion between two polymers obtained through this analysis has been found to be a useful parameter to elucidate the phase-separated structure. On the basis of these results, it is concluded that the PBA/PMMA polymer particles have a rather incompletely phase-separated core-shell type structure but the addition of an appropriate amount of AMA improves such a structure by confining the distribution of PMMA domains around the surface of the polymer particles probably as a result of the preferential crosslinking in the PBA phase.

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This study introduces a technique developed for the quantitative measurement of the kinetics of dispersed phase particle coalescence in polymer blends. The method has been shown to be useful and reproducible for the study of morphology development and stability in polymer melt blending. Using this technique, we examined the relative importance of reactive compatibilizers, shear history and matrix phase viscosity on the morphological stability of PC/SAN blends.

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Morphology and viscoelastic properties of a compatibilized epoxy/thermoplastic polymer blend were investigated. Transmission electron microscopy (TEM) showed that the introduction of the compatibilizer significantly reduces the size of the thermoplastic dispersed phase. Dynamic mechanical spectrometry (DMS) revealed an additional loss peak at about 333 K at 1 Hz in the compatibilized ternary blend spectrum which is detailed as the first unequivocal observation of a 'micromechanical transition’ in a compatibilized thermoset/thermoplastic blend. In addition, the influence of thermal treatments (which were established according to structural recovery considerations, i.e. accelerated physical aging at T g ¹ 20 K and 'refreshing’ process at T g þ 20 K) on the viscoelastic behavior (amplitude and temperature position) of the additional loss peak was studied. These investigations revealed that the occurrence of the 'micromechanical transition’ on DMS spectra depends significantly on the thermal history of the sample and leads to the assumption that the viscoelastic behavior of the interphase relaxation is associated with the conditions of confinement of the components in the interphase zone.

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The interaction of a sample of poly(methacrylic acid) with copper ions is investigated using various techniques: light and X-ray scattering, viscosimetry and fluorescence. The measurements were performed in the solubility domains and the regions where phase separation occurs were determined as a function of pH and copper/polymer ratio. We conclude that copper is mainly bound on the polymer through the formation of binuclear complexes implying pairs of adjacent carboxylates far along the chain. This induces a strong collapse of the chain at low ionisation degree and partially hinders the chain expansion at high pH. Fluorescence measurements can be interpreted through the existence of two different transitions: local and global transitions.

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The relationship between the diffusion behavior and the solvent induced crystallization (SINC) was investigated. We have also studied the crystalline structures of PEN crystallized by solvent and compared them with those of thermally crystallized PEN. The diffusion behavior of dioxane at 408C and 608C is not pure Fickian but apparent Fickian where diffusion is controlled by crystallization. The diffusion behavior at 258C is also not pure Case II. The diffusion behavior in DMF is similar to that in dioxane. The samples treated in dioxane above 408C, which show the Fickian diffusion behavior, exhibit a-crystal and spherulitic texture. The sample treated in dioxane at 258C, which show the Case II diffusion behavior, mainly exhibits b-crystal and the amoebae structure. The samples treated with DMF mainly show the a-crystal, irrespective of treatment temperature. The change of diffusion behavior by varying the treatment temperature affects the crystallization conditions, and crystalline form in SINC is changed by the characteristic of solvent.

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