1994 рік

The conformational and intermolecular contributions to the residual enthalpy AH o and entropy S~ at 0 K for amorphous nylon-6 and nylon-6,6 were investigated on the basis of the derivation of a new relationship between Cp and C,,. It was found that AH o contains only the intermolecular enthalpy for CONH residues in amorphous nylon-6 and nylon-6,6. The conformational contribution to S~ consists, on the basis of the conformations, of 49 kinds of rotational isomeric states for nylon-6 and 2401 (49 x 49) kinds for nylon-6,6, independently of temperature. The intermolecular contributions to S~ are only due to CONH residues in these polymers. Next, through the investigation of the conformational contributions to the glass transition, the possibility of ordered regions in nylon-6 and nylon-6,6 glasses was explored. The existence of localized and ordered parts with enthalpies of 40.1 kJ tool- ~ for nylon-6 and 80.7 kJ mol- ~ for nylon-6,6 is predicted. The enthalpies of the localized ordered parts are somewhat larger than the glass transition enthalpies of 37.6 kJ mol- 1 for nylon-6 and 75.2 kJ mol- i for nylon-6,6, respectively

Детальніше...  

Thermal ageing of hydroxyl-terminated polybutadiene propellant binders was carried out at various temperatures between 50 and 100°C. The changes caused by this treatment in properties such as melt viscosity, functional end-groups, molecular weight, tensile strength, elastic modulus and ultimate elongation were examined. The viscosity and average molecular weight increased with the ageing temperature and ageing period. A decrease in ultimate elongation and an increase in elastic modulus were observed. Tensile strength of the matrices prepared by curing hydroxyl-terminated polybutadiene with isophorone diisocyanate did not change. Lifetime for usability was predicted from the application of the Arrhenius equation to be 7 years.

Детальніше...  

Through novel metallation reactions of active hydrogen compounds by lithium diisopropylamide, followed by coupling reactions between the carbanion and organosilyl chloride, new organosilicon-containing oligomers with reactive double bonds were synthesized. The silicon-containing oligomers obtained have ultra-violet (u.v.) crosslinking ability and can be expected as ultrathin films for gas separation membranes. Using 4-methylstyrene (MST) and/or allyltrimethylsilane (AS) as active hydrogen compounds, organosilicon-containing oligomers with reactive double bonds in the main chain and/or in the side chains were synthesized. By changing the molar ratio of MST/AS, it was found that the stiffness of the oligomers can be controlled. U.v. irradiation induced the crosslinking reactions of the organosilicon-containing oligomers with pendent vinyl groups.

Детальніше...  

Poly(diaza-3n-crown-n)s having hydroxyethyl side arms (PDC,s: n = 5-7) were prepared, and their effects on the ionic conductivity of both inorganic salts and cation conductive polymers were analysed. A series of alkali metal perchlorates (MC10,,: M = Li, Na, K, Rb, and Cs) were mixed with the PDC. materials. However, although ionic conductivity better than 10-6Scm - ~ above 60°C was achieved, no effect was seen of any specific coupling of the cation and the crown cavity size on the ionic conductivity. This was probably due to the contribution of the anion conduction. In order to neglect the effect of anion migration, cation conductive polymers were mixed with the PDC, materials. K + and Na + showed the lowest ionic conductivity in PDC 6 and PDC 5, respectively, reflecting stronger interactions with crown ethers having more suitable cavity sizes. The presence of crown ether units in the polymer was also suggested as being responsible for accelerating the dissociation of salts with cations which were smaller than the size of the crown ether cavity.

Детальніше...  

In order to elucidate the structure of poly(vinyl alcohol) (PVA) gels, the gels studied were aged for as long as 500 days at 30°C. The original gel was formed from PVA solutions in a mixed solvent of dimethylsulfoxide (DMSO) and water by chilling at -34°C for one day. The aged gel was shown to have a well grown crystal phase, in that the melting endotherm from differential scanning calorimetry could be clearly separated into two or three components, which were named A, B and C, in order of melting temperature. The enhancement of the gel modulus and the solvent exclusion observed in the aged DMSO/water gels could be atrributed to phase separation, which facilitates crystallization into the B and C components. The A component was shown not to bear a strong relationship to the high modulus and the exclusion of solvent, although it may be the most common crystallite grown from PVA solutions.

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The effect of compression on the fluorescence and Raman spectra of poly(p-phenylene benzobisoxazole) (PBO) fibre and a PBO/amorphous nylon blend has been investigated qualitatively at various excitation wavelengths. A substantial red-shift in the fluorescence maxima is observed upon increasing pressure both in PBO fibres as well as in the PBO/amorphous nylon blend. The shift is consistent with that observed for aromatic molecular crystals. This observation strongly suggests that certain features in the fluorescence emission are due to interchain interactions.

Детальніше...  

Optically active copolymers of racemic 4-acryloyloxy-~-methylbenzoin methyl ether (AMBE) with ( - )-menthyl acrylate (MtA) have been radically prepared. The reactivity of the comonomers suggests that the copolymers display a certain tendency to an alternating distribution of the co-units. Optical activity at 589 nm of the copolymers seems to exclude any stereoselectivity and stereoelectivity during the copolymerization process. Chiroptical properties indicate that an induced optical activity on benzoin methyl ether chromophores occurs. Circular dichroism Ic.d.) data, connected with n--,rr* and rt--,Tt* electronic transitions of the benzoin methyl ether moiety, suggest that the observed ellipticity is substantially due to isolated AMBE units. C.d. features indicate that the macromolecules, due to the presence of optically active MtA co-units, assume conformations with a prevailing handedness for sections not sufficiently long to provide cooperative interactions between side-chain benzoin methyl ether chromophores disposed along the backbone with a mutual chiral geometry suitable for exciton couplings.

Детальніше...  

Dynamically cured blends of butyl rubber (IIR; isoprene-isobutylene rubber) and anhydride-grafted polypropylene (PP) of various component ratios and curative loadings were prepared by melt mixing. Evidence from dynamic mechanical analysis and phase-contrast microscopy suggested that these blends were heterogeneous, with the PP phase being continuous. Damping characteristics of these blends in the temperature range of - 60 to 0°C were strongly affected by a liquid-state relaxation peak of the IIR phase. It was observed that the presence of a continuous PP phase tends to suppress the intensity of this characteristic loss peak and shift it towards lower temperatures; on the other hand, the crosslinking of IIR has little effect on the intensity of the broad loss peak but tends to shift it towards higher temperatures. These observations were interpreted in terms of effects of thermal misfit stress and crosslinking on the liquid-liquid transition of the IIR phase

Детальніше...  

The crystal transformation of styrene-butadiene block copolymer, which has the attribute of shape-memory, has been studied. It is demonstrated from differential scanning calorimetry and wide-angle X-ray diffraction measurements that reversible crystal transformation takes place with temperature; two distinct crystal forms exist above and below the crystal transformation temperature of ~45°C.

Детальніше...  

Transketalization reactions between the diketals of 1,4-cyclohexanedione and the diketonides of pentaerythritol yield a spiropolymer which is insoluble in all solvents tried, but which can be hydrolysed to 1,4-cyclohexanedione and pentaerythritol. At short reaction times, oligomers such as 3,3,21,2 l-tetrameth yl- 1,5,10,14,19,23,26,29-octaoxapentaspiro['5.2.2.2.2.5.2.2.2.2] untriacontane can be isolated. However, all attempts to achieve a genuine equilibrium between the monomers, oligomers and polymer were fruitless. The 13C cross-polarization/magic angle spinning (CP/MAS) n.m.r, spectrum of the polymer shows extra lines relative to those of soluble model compounds; this is probably due to a slow ring inversion of the 1,3-dioxane rings in the solid polymer

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