1999 рік

A study was made of the structure and physico-mechanical properties of epoxy polymers obtained using different curing agent–oligomer ratios. The results were analysed within the framework of the cluster model of structure of the polymer amorphous state. It was shown that the model under consideration can be used for determining the quantitative structure–property relationships for cross-linked polymers.

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The effect of surface treatment of glass beads with a silane coupling agent and the filler content on the notched Izod impact properties of the filled polypropylene (PP) composites has been investigated. It was found that the impact fracture energy of the composites, E IC, increased with increasing the volume fraction of glass beads, f f; the influence of surface treatment of glass beads on E IC was insignificant; the brittle– ductile transition (BDT) phenomenon occurred when f f was about 10%. A modified percolation model for BDT in thermoplastic–rigid particle blends is proposed under the basis of predecessors’ work. The results show that the BDT of the composites in impact can be considered as a percolation process.

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The influence of the chain extension in the glassy state on the glass transition temperature was investigated for poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) fibers. The extended samples were prepared by drawing at just above the glass transition temperature and subsequently cooling to the room temperature under a constant length condition. The glass transition temperature was measured using differential scanning calorimeter without externally applied stress to the sample. The depression of glass transition temperature with increasing the extension ratio was observed for both PET and PEN fibers. An equation for the depression of glass transition temperature is derived by modifying the DiMarzio’s theory and applied to the experimental data. In lower extension for PET fiber, the equation predicts successfully the depression of glass transition temperature in accordance with the empirical result. However, for the PEN fiber and the highly stretched PET fiber, the empirical data deviates from the prediction, because of the crystallinity increment of the fiber during the drawing process.

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The curing process of a dicyanate resin system was investigated by a positron-annihilation lifetime technique (PA). Based on the observation of PA, it was shown that the size of free volumes of cured resins became larger as the curing reaction proceeded. This result was supported by a change in the physical properties related to the size of free volumes, such as a decrease in the specific gravity, a decrease in the dielectric constant and an increase in the water pick-up rate with increasing the decree of the cure. It was therefore found that the curing reaction of dicyanate resin proceeded through a reaction of cyanate groups to form a larger size of free volumes.

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The influence of the bridging group between the mesogenic group and the oxirane ring on the curing behavior and the liquid crystalline phase of liquid crystalline epoxy (LCE) resins was investigated. Two LCE resins containing ether and ester bridging groups were synthesized for this purpose. The ether linkage stabilized the liquid crystalline phase of the LCE and the LCE network more than the ester linkage. The retardation effect of curing was observed in LCE with the ester linkage. The LCE with the ether bridge showed higher mechanical and thermal properties than that with the ester bridge. The liquid crystalline phase of the LCE monomer remained after the crosslinking reaction and it was stable up to 300°C.

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Mono-carboxy terminated polystyrene oligomer (MCPS) and di-carboxy terminated polystyrene oligomer (DCPS) were prepared by anionic polymerization. Viscometry and dynamic light scattering (DLS) studies show that both MCPS and DCPS can interact with poly(4vinyl pyridine) (PVPy) via hydrogen bonding to form soluble graft-like complexes in CHCl3. The marked differences in the viscosity– composition behaviour, intrinsic viscosities and hydrodynamic radius distributions f(Rh) between MCPS/PVPy and DCPS/PVPy blend solutions proved that the two carboxyl ends in DCPS provide much stronger ability for complex formation than the mono carboxyl end in MCPS does.

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Monte Carlo methods were tested with respect to their potentials and limitations for the modelling of the kinetics of polymerization reactions and especially with regard to the various distributions of the final product. Presented here is a model concept based on a critical comparison of algorithms already published in the literature. The concept can be used generally and guarantees a high level of formalism and, therefore, a minimum developing time. It is based on the simulation of the time behaviour of molecules in small volume increments of the reaction mass and permits the calculation of kinetics as well as different product distributions. In the case of free radical polymerization reactions, computation times may be reduced if the chain length of the polymer molecules are calculated from the lifetimes of the radicals. The model concept has been tested on the modelling of several different polymerization reactions, such as a heterogeneous polycondensation, an inverse emulsion polymerization and a thermal polymer degradation.

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Thiophene- and benzene-modified nickel poly-yne polymers 1–5 were characterized by gel permeation chromatography, infrared spectroscopy and X-ray photoelectron spectroscopy. The polymers, being highly soluble in common organic solvents, exhibit intense fluorescence upon excitation by ultraviolet–visible light at room temperature. The emission intensity of the polymers with thiophene-2,5-diyl is 8–277 times stronger than that of the analogous polymers without thiophene-2,5-diyl. Transient luminescence was also investigated.

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The application of heteronuclear chemical shift correlation (HETCOR) NMR allowed us to correlate the homodecoupled methine proton with the methine carbon signals of poly(rac-lactide) and poly(meso-lactide), and made it possible to perform a detailed analysis of 1H NMR spectra (homodecoupled) and to ascribe the signals to configurational pentads. The assumption made by Chisholm and coworkers [Chisholm et al., Chem. Comm. 1997, p. 1999] that the previous assignment of methine carbon signals in 13C NMR spectra was incorrect appeared to be wrong.

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A series of alkyl pyridinium bromide maleate diester surfmers were synthesised together with their saturated non-polymerisable succinate analogues. Each series consisted of four surfactants with the maleate or succinate function at different positions on the alkyl chain with the integrated length of the alkyl chain being more or less constant. The surface activity was evaluated and the critical micelle concentration (cmc) was found to be dramatically affected by the position of the maleate or succinate group. For the cases in which the pyridinium ring was close to the carboxylate group of the maleate or succinate, all the experimental observations could be explained if there was an interaction between the cationic N centre and the ester(s) reducing the charge density of the headgroup and, for example, allowing a closer packing of the molecules at the air–water interface. Overall, however, these species behaved similarly to conventional surfactants such as cetylpyridinium bromide. Those species in which the maleate or succinate group was placed in the terminal position of the hydrophobic tail showed abnormally high (⬃ х 10) critical micelle concentrations suggesting that the polar group in this position reduced considerably the overall hydrophobic nature of the surfactant tail. These molecules also appear to adopt a looped conformation at the air–water interface.

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