1993 рік

Homopolymer poly(ethylene terephthalate) (PET) and nylon-6 (PA-6) and a blend (1:1 by weight) of these polymers, are each extruded as strips and ultraquenched from the melt. After zone drawing and additional annealing at temperatures, T~, of 220 or 240°C for 5 or 25 h in vacuum, the samples are studied by differential scanning calorimetry, small-angle and wide-angle X-ray scattering, and mechanical testing. It is found that all components in the blend are oriented and that the perfection of the structure develops with increasing Ta up to 220°C. At T a = 240°C, isotropization of the PA-6 component is observed, while the orientation of the PET is preserved. A microfibrillar reinforced composite is obtained, with mechanical properties as high as those of glass-fibre-reinforced nylons and surprisingly large (about 100 x ) deformability. It is shown that during thermal treatment for longer time, in addition to physical processes (crystallization and relaxation), chemical interactions (additional condensation and exchange reactions) take place at the interfaces, resulting in the formation of PET-PA-6 block copolymers playing the role of compatibilizers. Further interaction between PET (partially) and PA-6 (completely) amorphous phases leads ultimately to the involvement of the entire amount of PA-6 in the block copolymers, thus converting the starting PA-6 matrix of the microfibrillar reinforced composite into a PET-PA-6 copolymer matrix

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The influence of reaction conditions on the preparation of poly(ether ketone) by Friedel-Crafts acylation of diphenyl ether and isophthaloyl chloride in 1,2-dichloroethane with aluminium trichloride as a catalyst was examined. The following factors were considered: catalyst quantity, reaction temperature, monomer ratio and polymer concentration. One of the characteristics of this reaction was precipitation of polymer/catalyst complexes. Polymerization proceeded even in the precipitate by the reaction between the chain-ends. At low polymer concentrations, crystalline grains appeared, and the reaction between the chain-ends was accelerated. As the polymerization of the precipitate proceeded, the precipitate could contact more effectively with fresh solvent because the hydrogen chloride formed by the acylation was easily removed from the reaction site.

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Copolyaramides with 2,5-di-n-hexyl terephthalic acid residues as comonomers were synthesized. Partial phase diagrams were measured for mixtures with concentrated sulfuric acid in the range between 8 and 20% w/w of polymer. Lyotropic phases were observed, but in comparison to homopoly(p-phenylene terephthalamide) the clearing temperatures are lower and the critical concentrations for the formation of the lyotropic nematic phase are increased. The existence of a master curve for the clearing temperature as it depends on the concentration of the components of both homo- and copolymers illustrates that the side chains act mainly as an 'attached solvent' to the rigid main chains.

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Reactive compatibilization of immiscible polymer blends has been attracting a very considerable research interest in the past few years. While a wide variety of functionalized polymers having acidic groups are commercially available, potentially reactive polymers containing basic functional groups have rarely been developed. In this study, glycidyl methacrylate (GMA), 2-hydroxyethyl methacrylate (HEMA), 2- hydroxypropyl methacrylate (HPMA), t-butylaminoethyl methacrylate (TBAEMA), dimethylaminoethyl methacrylate (DMAEMA), and 2-isopropenyl-2-oxazoline (IPO) were melt grafted onto a polypropylene (PP) homopolymer. The effectiveness of these functionalized PPs as compatibilizers for PP/(acrylonitrileco- butadiene-co-acrylic acid) rubber (NBR) blends was evaluated in terms of improvement in impact properties and blend morphology. It has been found that IPO and GMA are effective in compatibilizing the PP/NBR blends, with a nine-fold improvement in impact energy over pure PP and an uncompatibilized PP/NBR blend. The other functional groups are much less effective for the blend system where carboxylic acid is the coreactive group

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Numerous phosphorus-containing aromatic polyesters were prepared by polycondensation of silylated diphenols with dicarboxylic or phosphoric acid dichlorides. Phenyl phosphate and naphthyl phosphate, phenyl- or methylphosphonate groups were incorporated into poly (phenylhydroquinone terephthalate). Regardless of the substituent attached to the phosphorus atom the nematic phase disappeared when more than 20 mol% of the terephthalic acid was replaced by phosphoric or phosphonic acid units. Furthermore, phenylphosphonic acid was incorporated into various thermotropic copolyesters. It was found in all cases that the stability of the mesophase depends on the percentage of phosphorus and on the length of the repeating unit

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Application of dielectric, mechanical and rheological measurements to the characterization of cure and phase separation in a thermoplastic modified epoxy resin is reported. These data indicate that the dielectric technique is not only useful for monitoring changes in network dynamics during the process of cure, but can also provide valuable information on the phase separation of the occluded phase. The paper discusses the modelling of the dielectric data, and considers the importance of understanding the relationship between morphology and mechanical properties

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The physical properties of the nylon with the longest number of methylene segments, nylon 13,13 have been characterized. Studies are reported of thermal analysis, X-ray scattering and for mechanical properties includin~ hardness. The crystal of nylon 13,13 has been found to have a monoclinic form with a=4.9 A, b=9.22A, c=34.40A and fl= 121.08 °. Also, studies were carried out on the mechanical properties of nylon 13,13 that had been uniaxially drawn by solid-state extrusion at 125 and 135°C. The highest draw ratio obtained was 4.5. The maximum melting point, heat of fusion and amorphous density were estimated to be ~> 183°C, 230J g-1 and 1.01 g cm -3, respectively. The crystallinity, melting temperature and tensile modulus increased with draw ratio. The glass transition temperature of the undrawn polymer was 56°C. For the sample with a draw ratio of 4.0, the tensile modulus and the X-ray crystal orientation function reached 2 GPa and 0.94, respectively.

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In highly oriented polymers, stress can stabilize fibres against melting by favouring the low entropy fibrillar state against the high entropy melt. In this work we have investigated the thermal stability of gel-spun ultra-high modulus polyethylene subjected to tensile stress. The Daresbury X-ray synchrotron radiation source and optical microscopy have been utilized to follow dynamically the transformation, melting and recrystallization of fibres, under optimum conditions of controlled stress. The orthorhombic phase is stable up to 164°C, after which the crystals transform into a hexagonal phase which can be stable up to temperatures as high as 179°C. Whilst this is the greatest thermal stability reported for the orthorhombic phase, the question of the ultimate stability is still unanswered and is presently limited by the effectiveness of the stress transfer to the fibrils.

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Grafting of maleic anhydride (MAH) onto isotactic polypropylene (PP) was performed by melt mixing in a laboratory-scale internal mixer with the addition of dicumyl peroxide (DCP) as an initiator. The efficiency of the graft reaction (estimated by use of Fourier-transform infra-red spectroscopy) tends to decrease with increasing MAH or DCP content; the optimal composition for the present reaction system appeared to be at a low DCP level and a moderate MAH loading. Concurrent with the grafting reaction, PP undergoes significant chain scission as indicated by the decrease in mixing torque and supported by the dynamic rheological evidence. The first addition of MAH to the reaction mixture enhanced the DCP-initiated chain scission; upon further addition of MAH, the scission reaction became less severe. These observations were explained in terms of competition between chain transfer/fl scission and bimolecular coupling of radical intermediates

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The effects of physical ageing on the mechanical properties of a liquid-crystalline copolyester (LCP) were determined. Creep measurements in torsion as a function of ageing time were performed on macroscopically unoriented samples in the temperature range of -60 to 180°C. Below the glass transition temperature (Tg-~ 100°C), the results indicate physical ageing effects analogous to those of flexible polymers. However, the curvature exponent of the compliance as a function of creep time of the LCP is distinctly smaller. Above Tg, physical ageing remains present while additional annealing effects arise. The molecular interpretation of the time dependence of mechanical properties in LCPs cannot rely upon free-volume concepts as in flexible polymers, but might be based on new structural models that were recently introduced

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