1999 рік

The morphology, deformation and failure behaviour of new high-performance polyimide (PI) fibres were examined by scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD) and tensile measurements. PI fibres were prepared from rigid aromatic diamines p-phenylenediamine (PPh) and 2,5-bis(4-aminophenyl)-pyrimidine (2,5PRM) and semi-rigid 4,4 0 -oxybis(phthalic anhydride) (DPhO) by wet-spinning of the N,N-dimethylacetamide solutions of their precursor poly(amic acids) in coagulation bath followed by thermal imidization at 4008C. The tensile properties and drawability of copolyimide (coPI) fibres were better than those of homopolyimides (homoPI). The improvement in fibre modulus and tensile strength of the coPI fibres can be explained by the microblock structure on the X-ray level and composed morphology on the macro level. Moreover, changes in the supermolecular structure and apparent fibril sizes, character of morphology, quantity of interfibrillar links, which affect the fracture mode were observed with the different composition of coPI.

Детальніше...  

Poly(2-trimethylsilyl-2-propyl methacrylate) was synthesized and evaluated as a potential dry-developable chemically amplified photoresist. The deprotection of 2-trimethylsilyl-2-propyl group of the polymer takes place in the exposed region after post-exposure bake. The difference of silicon content between the unexposed region and exposed regions is large enough to form patterns using oxygen reactive-ion etching. The etching selectivity of the unexposed region to the exposed region was 142.

Детальніше...  

The pulsed field gradient spin echo technique has been used to measure the self-diffusion coefficients of 7Li, 19F and protons in two electrolyte solutions, based on LiCF3SO3 in either tetraglyme or N,N-dimethylformamide, respectively. In addition, the ionic conductivities were determined by ac conductivity measurements and the viscosities with an Ostwald viscometer. Predicted values for the ionic conductivity were obtained from the n.m.r. diffusivities using the Nernst–Einstein equation and compared with those from direct measurements, to provide estimates of the degree of ionic association as a function of temperature and salt concentration. The possible correlations between solution viscosity and the self-diffusion coefficients of the ions were explored on the basis of the Stokes–Einstein equation. Finally, the results were considered in the light of previously reported Raman spectroscopy measurements and in terms of the Walden product of the molal conductivity and viscosity of the electrolyte.

Детальніше...  

The evolution of blend morphology during compounding in an internal mixer was investigated using transmission electron microscopy and scanning electron microscopy. Emphasis was placed on investigating the effects of viscosity ratio, blend composition, and processing variables (temperature, rotor speed, and mixing time) on the evolution of blend morphology in five blend systems: (i) nylon 6/high-density polyethylene (HDPE), (ii) poly(methyl methacrylate) (PMMA)/polystyrene (PS), (iii) polycarbonate (PC)/PS, (iv) PS/HDPE, and (v) PS/ polypropylene (PP). These blend systems were chosen on the basis of the difference in the melting temperature (Tm) between two crystalline polymers (nylon 6/HDPE pair), the difference in the 'critical flow temperature’ (Tcf) between two amorphous polymers (PMMA/PS and PC/ PS pairs), or the difference between the Tcf of an amorphous polymer and the Tm of a crystalline polymer (PS/HDPE and PS/PP pairs). The Tcf of an amorphous polymer is de facto equivalent to the Tm of a crystalline polymer in that from a rheological point of view an amorphous polymer may be regarded as being a 'rubber-like solid’ at temperatures below Tcf and a 'liquid’ at temperatures above Tcf, which is approximately 558C above the glass transition temperature (Tg) of an amorphous polymer. We observed a co-continuous morphology in PMMA/PS, PC/PS, PS/HDPE and PS/PP blends when the melt blend temperature was above the Tg, but below the Tcf of the constituent amorphous components, and a dispersed morphology when the melt blending temperature was increased far above the Tcf of the constituent amorphous components. Further, we found that the formation of a co-continuous morphology depends on blend composition and the viscosity ratio of the constituent components at a specified melt blending temperature. Most importantly, we have reached the conclusion that a co-continuous morphology is a transitory morphological structure that appears when a phase inversion takes place from one mode of dispersed morphology to another mode of dispersed morphology. The mode of a dispersed morphology is found to depend upon the blend composition and the viscosity ratio of the constituent components.

Детальніше...  

Syndiotactic polystyrenes (sPS) with different molecular weights were hydrogenated over the Ni/SiO 2 and Pd-BaSO 4 catalysts. Although the Ni catalyst yielded a completely hydrogenated sPS with a lower molecular weight, the hydrogenation of sPS with a high molecular weight was incomplete. On the other hand, the Pd catalyst was capable of hydrogenating sPS with a high molecular weight. However, the hydrogenated sPS (HsPS) was found to contained a small quantity of isolated styrene units. From a detailed analysis of the HsPS by differential scanning calorimetry (d.s.c.) and X-ray, it was revealed that this HsPS has a potential as a crystalline material with an excellent heat-resistance.

Детальніше...  

The mechanical properties and phase morphology of ternary blends of nylon 6 with rubber, e.g., maleated ethylene-propylene random copolymer (EPR-g-MA) or maleated styrene-(ethylene-co-butylene)-styrene (SEBS-g-MA), and a rigid but brittle imidized acrylic polymer (IA) are explored. The objective was to investigate blends which have independently dispersed rubber and rigid polymer particles in a nylon 6 matrix. The amount of rubber was fixed at 20%, while the IA to nylon 6 ratio was varied. Addition of imidized acrylic polymer particles to nylon 6 toughened by EPR-g-MA particles leads to increased stiffness and room-temperature impact strength and does not change the ductile-to-brittle transition temperatures up to a critical level. Similar improvements in stiffness and room temperature impact strength were found for nylon 6 toughened by SEBS-type rubber; however, the low temperature impact properties were not as good.

Детальніше...  

High resolution solid state 13C and 29Si CP/MAS NMR was used to investigate the grafting mechanism, morphology and interfacial mobility of polycarbonate (PC) oligomer and bisphenol A grafted onto silica surfaces. It was previously shown that interface modification via grafting led to composites with increased hydrolytic stability and interfacial toughness. The NMR experiments were carried out to determine the nature of the bonding of the reactants to the glass surface and to characterize the relaxation properties of the reacted species. The NMR spectra demonstrate differences between the neat and grafted PC oligomer that suggest strong bonding. A model compound, bisphenol A, was used to resolve signal overlaps caused by repeat units and to verify the formation of primary bonding at the silica surface by the existence of a downfield shift of the C4 resonance peak and other changes in the spectrum. Proton spin-lattice relaxation times in the rotating frame offer secondary evidence of the formation of Si–O–C bonds on the silica surface. The proton spin-lattice relaxation of the grafted molecules were characterized by a bimodal distribution of relaxation times, while unreacted molecules were represented by a single relaxation time. Temperature dependent studies show that the oligomer loses mobility as a result of grafting, and that the transition responses of the material are lost. The grafted material is visualized as a low density monomolecular layer of covalently bonded material.

Детальніше...  

Characterisation of the role of an active environment of use in an industrial Environmental Stress Crack Resistance (ESCR) test has been carried out during the tensile deformation of polyethylene samples. We intended to map the presence of the active environment within the material using Raman and infrared spectroscopy. We found Raman not suitable for the detection of this environment inside the sample while by IR the environment seemed to be predominantly present within the transition fronts of the material. A stress-induced environment diffusion mechanism is suggested. By scanning electron microscopy (SEM) differences in the deformation process between drawing in air or in detergent became apparent. These results suggest that the environment penetrates into the sample during the necking process, stabilising crazing. At the molecular level it is likely that chain slip and unravelling of molecular disentanglements are facilitated. All these observations may also be operative during the ESC phenomenon as samples are subjected to stress, resulting in crazing.

Детальніше...  

A series of the ruthenium(II) complex and viologen-containing partially quaternized poly(1-vinylimidazole)s with various degrees of quaternization (RuVQPIms) and various lengths of the alkyl side-chains [CnRuVQPIms:n ˆ 4(butyl),8(octyl),12(dodecyl),16(hexadecyl)] have been synthesized and characterized using UV–Vis absorption and luminescence spectroscopies. The effects of quaternization and length of the alkyl side-chains on the photosensitized charge separation using these metallopolymers have been investigated in methanol. The photosensitized charge separation reaction took place through an intrapolymer process for all systems. In the cases of the RuVQPIms having a low degree of quaternization and short alkyl side-chain, the initial rate of the viologen radical formation linearly depended on the polymer concentration with two stages, while the RuVQPIm having a high degree of quaternization and long alkyl side-chain showed only one-stage dependence. Further, the rate of the second stage was larger than that of the first stage. The dependence with two stages would be caused by aggregation at a high polymer concentration through the interpolymer van der Waals interaction. The stronger interaction induced by increases in the number and length of the alkyl side-chains on the polymer backbone decreased the flexibility of the viologen residues; consequently, the enhancement of the rate in the second stage was not observed.

Детальніше...  

The influence of drying methods on the micromeritics, phase transition, deswelling/reswelling process and surface topography of poly (Nisopropyl-acrylamide) (PNIPAAM) microgel beads was investigated. Three different drying methods (quick-freezing, slow-freezing and oven-drying) were applied to prepare the dried PNIPAAM microgel beads. Undried PNIPAAM microgel beads were used as control. The results indicate that although different drying methods significantly influenced the particle size distribution, deswelling/reswelling volume, surface topography and morphology of PNIPAAM microgel beads, it did not seem to affect the lower critical solution temperature (LCST) of 328C–348C and molecular interaction in PNIPAAM microgel beads. According to ATR/FT-IR/DSC microscopic study, above the LCST, the free form of non-hydrogen bonded CyO band and intra-molecular hydrogen bonding played a dominant role in the molecular structure of PNIPAAM microgel beads, which was contrary to our previous study in which the non-hydrogen bonding contributed less to the molecular structure of PNIPAAM aqueous solution without a cross-linking agent.

Детальніше...