1999 рік

Several b-polypropylene (b-PP) samples were stretched to various strains at room temperature. The morphologies of the deformed specimens were studied by scanning electron microscopy and transmission electron microscopy. The deformation was highly inhomogeneous in the b-PP specimens. In the early stage of deformation, horizontal lamellae were stretched to separation and deformation bands were formed within a spherulite in some regions. The deformation bands coalesced as strain increased. Near the yield point, some deformation bands developed into crazes across the spherulite boundaries. Meanwhile, melting spots and shear bands were found in the yielded sample. However, the main cause of failure was cracking across the specimen.

Детальніше...  

Time of flight mobility measurements were carried out in thin films of solid solution of amorphous polycarbonate molecularly doped with N-isopropylcarbazole by using electron beam bombardment. The dependence of the hole drift mobility (m ) with the applied electric field was analysed in the scope of both, the Poole–Frenkel emission model and a density of state model which does not invoke the existence of charged traps. The experimental results were in just agreement with the Poole–Frenkel model through the whole range of the electric field used during the experiment; however, the agreement with the density of state model was evident only at fields greater than 0.8 MV/cm. To justify this behaviour, an additional consideration in the Poole–Frenkel model was proposed which allowed to conclude, that the circumstantial agreement with the density of state model at the highest range of electric field results from the fact that the traps become inoperative at this range of field, and not because the traps were really absent.

Детальніше...  

The rheological properties of polystyrene/poly(vinylmethylether) (PS/PVME) blend near the critical region and in the homogeneous region were investigated. The blend had a lower critical solution temperature (LCST) of 112°C obtained by a turbidity experiment using a light scattering (LS) apparatus at a heating rate of 1°C/h. Four different blend compositions (critical (30/70 PS/PVME by weight) and three off-critical (10/90, 50/50, and 70/30) as well as neat PS and PVME were prepared. For the critical composition, logarithmic plots of shear modulus (G 0 ) versus loss modulus (G 00 ) showed temperature dependence even in the homogenous region determined by LS, while those plots become temperature independent in the homogeneous region for off-critical compositions. Logarithmic plots of blend viscosity versus composition exhibited a negative deviation at constant temperature; however, these showed a maximum at a certain composition when the reference temperature is taken as fixed T ⫺ Tg (under approximately iso-free volume condition).

Детальніше...  

The crystal structure of the clathrate d form of syndiotactic polystyrene containing 1,2-dichloroethane is presented. Polymer chains in s(2/ 1)2 helical conformation and 1,2-dichloroethane molecules are packed in the monoclinic unit cell with axes a ˆ 17.11 Å, b ˆ 12.17 Å, c ˆ 7.70 Å and g ˆ 120° according to the space group P21/a. The crystalline density of the clathrate d form is 1.23 g cm ⫺3 with two chains (eight monomer units) and two 1,2-dichloroethane molecules inside the unit cell. Molecules of 1,2-dichloroethane occupy isolated cavities between the benzene rings of adjacent polymer chains and are essentially only in the trans conformation. The location and the conformation of the 1,2dichloroethane molecule are such that both chlorine atoms are sandwiched between two benzene rings of the same polymer chain.

Детальніше...  

Three copolymers with different emulsification efficacies were used as potential interface modifiers for an immiscible blend of linear low density polyethylene (LLDPE) and poly(vinyl)chloride (PVC). The specific interaction between blend components and the modifying copolymers was determined by measurements of interfacial tension and by inverse gas chromatographic (IGC) data, characterizing the acid–base properties of the polymers. Additional information on modifier effectiveness was obtained from blend morphology data. Acid– base pair interaction parameters, computed from IGC results, predicted the modifying potential of the two copolymers which emulsified the system, and were consistent with the morphology and interfacial tension results. IGC, however, did not distinguish between the emulsification qualities of the two good modifiers. The best of the three modifiers (P4VP-PIP) also increased the impact strength of the modified LLDPE/PVC system. The results indicate that specific (acid–base) interactions at component interfaces may represent a promising strategy for the choice of emulsifying agents for some immiscible polymer blends.

Детальніше...  

Reactive blending of polysulfone (PSU) and polyamide 6 (PA) was carried out at 20/80 weight ratio using a gram-scale mixer at 260°C. Maleic anhydride-grafted PSU (PSU–MAH) and phthalic anhydride-terminated PSU (PSU–PhAH), having almost same molecular weight (Mw = 20 k) and functional group content (ca. 90 mmol/g) were prepared and used. The particle size reduction process was investigated by light scattering and transmission electron microscopy (TEM). Both reactive systems yielded finer particle size via faster particle size reduction process, compared with non-reactive system. Attainable particle size was in 10 nm-order in PSU–PhAH system, while in submm scale in PSU–MAH system. TEM observation at early stage of reactive blending in PSU–PhAH system showed that the in situ formed PSU–PA block copolymers escaped from interface to form micelle in PA matrix. Such micelle formation was observed only in the meltmixed blend but not in a quiescently annealed blend, suggesting that the block copolymer prefer to locate at the interface under static condition but they are easily pulled out when PA-brushes are subjected to external shear forces during melt-mixing. The micelle formation leads to the fine dispersion of 10 nm level in the final blend. By contrast, the micelles were never observed in the PSU–MAH blend, in situ graft copolymer forming system, even at the late stages of the reactive processing. It suggests that the graft copolymer is highly resistant to be pulled out by the external forces. Then the graft copolymer seems to act as a simple emulsifier to attain the size reduction to sub-mm level.

Детальніше...  

Pentadiene-functional macromonomers based on poly (methyl methacrylate) (PMMA) and polystyrene (PS), obtained through a free radical addition-fragmentation reaction were copolymerized with styrene, methyl methacrylate (MMA) and methacrylic acid (MAA) to synthesise well defined graft copolymers. Thus, PMMA-g-PS, PS-g-PMMA and PS-g-PMAA of varying compositions and graft lengths were synthesised. The copolymerization kinetics revealed diminished reactivity of the pentadiene function of the macromonomer towards a given comonomer vis-à-vis the reactivities of the pentadiene monomer or the pentadiene function on the addition-fragmentation agent used to prepare the macromonomers. Methacrylic acid showed apparently reduced reactivity than MMA and the copolymerization of the former with PS-based macromonomer gave amphiphilic graft copolymers with different solubility characteristics. The reactivity of the terminal pentadiene-function of the macromonomer was found to be independent of its molar mass, although its reactivity was marginally diminished in comparison with pentadiene monomer. Low concentrations of high molar mass macromonomer led to the concomitant formation of homopolymers of the small monomer in the case of copolymerization with reactive monomers like MMA and MAA. The graft copolymers have been characterized by chemical methods and by GPC using multiple detectors.

Детальніше...  

Unique thermal treatments were performed and differential scanning calorimetry (DSC) and X-ray diffraction analysis were used to characterize the dominating crystal form(s) being developed in cold-crystallized syndiotactic polystyrene (s-PS) in comparison with meltcrystallized polystyrene. The DSC results revealed that there are three (or fewer depending on the temperature of melt-crystallization) sharp melting peaks (Peak-1, -2, and -3) for the melt-crystallized s-PS samples, but only one peak (broad-based) for the cold-crystallized s-PS (when scanned at 10°C/min). The X-ray result suggested that cold-crystallization at higher than 200°C (200 ⬃ 250°C) produced only a -type crystal (or majority). This is in distinct contrast with melt-crystallization, which produced a combination of a -type (Peak-2 and Peak-3) and b -type (Peak-1) crystals at lower temperatures (240°C or lower), or majority of b -type if at temperatures higher than 260°C.

Детальніше...  

Frequency-dependent dielectric measurements have been used to monitor and characterize the phase separation process in high-performance thermoplastic–thermoset blends of 2,6-dimethyl-1,4-phenylene ether (PPE) with an epoxy diglycidylether of bisphenol A (DGEBA) and 4,4-methylene bis(3-chloro-2,6-diethylamine) (MCDEA). The systems studied are 30, 45 and 60% PPE/DGEBA–MCDEA blends. The results are compared with dynamical mechanical measurements and the developing morphology. Both dielectric and mechanical measurements are shown to be good techniques to monitor the phase-separation process and the reaction advancement. Dielectric measurements monitor the buildup in Tg in both the PPE-rich continuous phase and in the epoxy-rich occluded phases. Dielectric measurements are advantageous as they can be made in situ continuously on a single sample throughout the entire cure process. The results show that the phase separation process initially occurs rapidly involving a large amount of the epoxy–amine diffusing into the occluded phase. The rate of the epoxy–amine reaction in the epoxy-rich 30% PPE mixture is approximately equal to that in the neat epoxy–amine system due to two opposing effects, a slower reaction rate due to dilution and a lower level of conversion at vitrification due to the presence of high Tg PPE. In the 60% PPE mixture, the dilution effect of the PPE has a large affect on the decreasing the reaction rate and achievement of vitrification. The continuous thermoplastic-rich phase is observed to vitrify first, followed by vitrification of the thermoset as occluded particles. Finally, the results show as evidenced by the size of the occluded particles and the composition of the continuous phase that the morphology is strongly influenced by the kinetics, diffusion, and viscosity conditions during phase separation.

Детальніше...  

Two quaternary equimolar alloys (C 22/C 26/C 30/C 34 and C 24/C 28/C 32/C 36) and three commercial products, which respectively consist of 23 and 33 consecutive n-alkanes with chain lengths between 20 and 52 carbon atoms, are studied by X-ray diffraction analyses. A single orthorhombic solid solution, identical to one of the two intermediate phases seen in binary n-alkane systems, is observed in two commercial products and in their 50–50 wt% mixture. The n-alkane molar concentrations and the long crystallographic c parameters have been determined and allow us to demonstrate that the molecule layer stacking periodicity is quasi-equal to the average length of n-alkane chains of these complicated mixtures: this periodicity corresponds to that of a hypothetical orthorhombic pure n-alkane whose equivalent carbon atom number is quasi-equal to the average carbon atom number of commercial multi-n-alkane mixtures. Discontinuous distributions of chain lengths lead to the observation of two or three orthorhombic phases in the quaternary alloys and the presence of an orthorhombic solid solution and of an amorphous solid in the third commercial multi-n-alkane product.

Детальніше...