1999 рік

Pseudopolyrotaxanes and polyrotaxanes of polyamide and the macrocycle cucurbituril are synthesized easily by interfacial polycondensation. With different diammonium ions and diacid chlorides a great variety of poly(amide rotaxane)s is obtained. The structure of the diacid chloride influences the possible motion of cucurbituril on the polymer chain. First attempts to characterize these polyrotaxanes using IR, DTA, 1H-NMR and elemental analyses are reported.

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The Young’s modulus or crystallite modulus of ca. 10 GPa has been obtained experimentally by the X-ray diffraction method for isotactic poly(methyl methacrylate) (it-PMMA) crystal along the chain direction. The modulus, calculated by the energy minimization method, for the double-stranded helix model of it-PMMA was 19 GPa, which was about twice as high as that of the single helix model, 11 GPa. This calculation indicated clearly a role for the intertwining of the two chains on the mechanical toughening of the polymer crystal along the chain axis, although the calculated value was an overestimation compared with the observed value.

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The relationship between glass transition temperature (Tg) and lateral force of amorphous polymer blends composed of components having Tg’s lower and higher than room temperature (295 K) was studied on the basis of lateral force microscopy (LFM). Although the lateral force for the homopolymer is deeply related to its surface viscoelastic property or Tg, the LFM results revealed that the lateral force dependence on the scan rate of the miscible polymer blends, [poly(methylacrylate)/poly(vinylacetate)] and [polystyrene/poly(vinylmethylether)], was similar with that of the component whose lateral force behavior shows the dependence on the scan rate, regardless of their Tg. This result suggests that the lateral force of miscible polymer blend reflects the sum of each component contribution, depending on the surface structure of the blend. Therefore, it was concluded that the information about surface structure can be obtained from the measured lateral force behavior of a miscible polymer blend.

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The extent of poly ε-caprolactone (PCL) incorporation into silica networks prepared by the sol-gel process depends on the HCl:tetraethoxysilane (TEOS) molar ratio and the H 2O:TEOS molar ratio, as well. The PCL incorporation increases with the concentration of the acid used as the catalyst. Dynamic mechanical analysis (DMA) indicates that increasing the acid concentration or decreasing the water content results in a higher glass transition temperature for the organic component in the hybrid materials, whereas the modulus does not change significantly. Small-angle X-ray scattering (SAXS) data agree with a nanoscopic phase separation of the two constitutive components: the organic polymer and the silica network. The characteristic length of this two-phase structure increases with acid content (except for the lower HCl:TEOS molar ratio of 0.05) and with water content (except for the higher H 2O:TEOS molar ratio of 2.0). The structure of the PCL/SiO 2 interface is mass fractal and the structure is more open when the acid content is lower or the water content higher.

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The fracture properties of blends of poly(butylene terephthalate), PBT, with acrylonitrile-butadiene-styrene materials, ABS, compatibilized by a methyl methacrylate–glycidyl methacrylate–ethyl acrylate terpolymer, MGE, have been characterized by Izod impact and singleedge notch, three-point bend (SEN3PB) type tests. The impact properties have been shown to be very sensitive to specimen thickness and mildly sensitive to notch sharpness. Blends containing 30 wt% ABS and molded into 3.18 mm samples are super tough in the absence of a compatibilizer; however, 6.35 mm specimens require higher ABS contents and compatibilization to achieve significant toughness. Low quantities of MGE (1 wt%) are required to produce super tough blends of 6.35 mm thickness; whereas, higher quantities of MGE result in a decrease in the impact strength. A dual mode of deformation during Izod impact testing has been observed for uncompatibilized blends molded into 6.35 mm samples where brittle failure occurs in the region of fracture initiation and ductile failure occurs in the region of crack termination. Similarly, a more brittle mode of failure occurs for SEN3PB samples with long ligament lengths and ductile failure for samples with short ligament lengths. The distance a crack can propagate and the size of the stress whitened zone created during Izod impact testing have been shown to be related to the impact properties determined by Izod and SEN3PB tests.

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Amorphous films of poly(ethylene 2,6-naphthalate) (PEN) were drawn isothermally at temperatures between 1308C and 1608C, more specially at 1458C up to the desired draw ratios, mainly to study structure formation during uniaxial drawing by differential scanning calorimetry. During drawing, a rigid phase structure was induced and the results were analyzed in comparison with stress–strain curves in order to relate the amount of induced rigid phase structure at the earlier-mentioned temperatures with the observed stretching behaviour. During the uniaxial drawing of PEN at temperatures between 1308C and 1608C, the amount of amorphous phase was linearly related to the square root of the extra first strain invariant. The stress–strain curves were characterized by a necking behaviour and the end of the yielding or necking was reached when the amount of induced rigid phase attained 50%. The rigid phase then acted as the continuous phase and the stress increased very strongly. The stretching behaviour of PEN was characterized more by the strain induced rigid phase formation than by the stress or strain induced crystallization.

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Polystyrene (PS) was completely immiscible with a liquid crystalline polymer (LCP), a copolyester of p-hydroxybenzoic acid and poly(ethylene terephthalate). As revealed by differential scanning calorimetry and scanning electron microscopy (SEM), chemically modified PS, sulfonated PS (SPS) and four of its salts, were miscible with the LCP. Each LCP/SPS blend had only one composition-dependent glass transition temperature (T g), from which and from the T gs of the SPS compounds, the T gs of the LCP component were found to be almost the same via the Fox equation. SEM observation showed that LCP/SPS 75/25 blends had a homogeneous texture with no discernible dispersed particles, while LCP/SPS 25/75 blends had dispersed, nanometre-sized particles which were aggregates of SPS anions as confirmed by X-ray photoelectron spectroscopy. Characteristic absorption shifts in the Fourier transform infra-red spectra of LCP/HSPS revealed that miscibility enhancement was caused by specific interactions between the carbonyl groups of LCP and sulfonate groups of the acid form of SPS.

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The effects of bromine substitution on the physical and gas transport properties were examined for five families of tetra-substituted glassy polymers: bisphenol A polycarbonates (PC), hexafluoro-polycarbonates (HFPC), hexafluorobisphenol-tertiary butyl isophthalates (HFBPtBIA), fluorenebisphenol-t-butyl isophthalates (FBP-tBIA) and bisphenol A-t-butyl isophthalates (BPA-tBIA). Additionally, the thermal response of the substituted BPA-tBIA polymers was explored to elucidate the effects of bromine substitution on the activation energies of permeation and diffusion and on the heat of gas sorption. Compared to its methyl-substituted analog, each bromine-substituted polymer had a higher cohesive energy density, a higher glass transition temperature and a lower oxygen-specific fractional free volume. Bromine substitution significantly reduced O 2 and CO 2 permeability and substantially increased both O 2/N 2 and CO 2/CH 4 selectivity. An increase in the activation energy of diffusion for N 2 compared to O 2, and for CH 4 compared to CO 2, may be credited for the majority of the selectivity gain. A new method for evaluating penetrant-dependent fractional free volume proved to be a valuable tool in determining the effects of structural changes on gas transport behavior.

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The mechanism for the conversion of the 13/4 helix into the 4/1 helix of poly(a -isobutyl b -L-aspartate) was simulated at the atomic level. A computational procedure based on a potential of mean force capable of creating multiple conformation states compatible with a given helical symmetry was used. Intermediate helical arrangements differing in 0.1 residues/turn were modeled and energetically evaluated to delineate the reaction coordinate. The conversion was found to proceed through poorly defined hydrogen bonded structures having an energy surplus of about 6 kcal/mol·residue. Results were consistent with experimental data and helpful for understanding fundamental aspects of the transition as it is observed in the solid state.

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Both viscoelastic and plastic properties were investigated on random copolymers of methylmethacrylate (MMA) and N-methyl-glutarimide (GIM) in the range 0–76 mol%. All the measurements were performed on samples quenched from the melt in order to break free from physical aging effects. Dynamic mechanical experiments were performed at very low deformation and temperatures ranging from - 150°C up to the glass transition temperature (T g) region. Increase in GIM amount improves the thermomechanical stability of the copolymers, as revealed by the increase of both T g and a relaxation temperature. In the b relaxation region, the E⬙ loss peak first decreases in amplitude with increasing GIM content and then broadens further and finally spreads out till the onset of the a peak at the largest GIM amounts. A quantitative analysis of the b relaxation phenomena was performed by considering the loss compliance J⬙ instead of the loss modulus E⬙. It turns out that in the low temperature range (¹80°C–0°C) the mechanical damping associated with the MMA motions is stronger for MMA– GIM than for MMA–MMA linkages; in addition, the mechanical damping associated with the motions of the GIM units is very low. By contrast, in the high temperature range (30°C to about 100°C), the mechanical damping associated with the MMA motions drops with increasing GIM amount, whereas a significant damping coming from the GIM units is observed. These results suggest that the b relaxation would mainly consist of MMA isolated motions at low temperature and of cooperative motions at higher temperature, involving the MMA units at GIM amounts lower or equal to 58 mol% and the GIM units at higher GIM content. The stress–strain curves were determined at low strain rate (2 х 10 -3 s -1) and temperatures ranging from - 120°C to T g. Analysis of the plastic deformation region shows that the yield stress decreases with increasing GIM amount at low temperatures. The opposite trend shows up on the high temperature side of the b relaxation, where strain softening peaks at intermediate GIM amounts. As a plausible explanation, the cooperative b motions, whenever they exist, are suspected to be responsible for the decrease of both yield stress and strain softening. These conclusions agree well with those of a previous study on methylmethacrylate-co-maleimide copolymers. They are also consistent with our earlier identification of the microdeformation mechanisms involved in the stretching of methylmethacrylate-co-N-methylglutarimide thin films.

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