1994 рік

The deformation behaviour of multilayered tapes based on polystyrene-poly(2,6-dimethyl-l,4-phenylene ether) (PS-PPE) and polyethylene (PE) layers is investigated for PS-PPE layer thicknesses varying from 50 down to 0.05/~m. Two (rather than one) transitions can be observed in decreasing the PS-PPE layer thickness (d). The first transition at d~ 1/~m is enabled by a stress transfer mechanism that is similar to the mechanism operating in fragmentation tests in fibre reinforced composites and is operative through the non-zero but still low level of interlayer adhesion (Gic~5Jm -2) between PS-PPE and PE. This can be exploited practically by the introduction of a significant level of interlayer adhesion via the incorporation of a diblock copolymer between the PS-PPE and PE layers which, finally, results in a multilayered system with a strain-to-break of pure PE. The second transition at 0.5/~m > d > 0.05/~m (dependent on the network density) is associated with a change in deformation mechanism from crazing to shear deformation as revealed by optical light microscopy during tensile testing. The strain-to-break below the second transition corresponds to a value comparable with the stretching of the entanglement network to its full extension (2max). The critical layer thickness found coincides with the experimentally determined critical thickness as already reported for the non-adhering core-shell rubber-modified PS-PPE systems in part 2 of this series. The absolute value of the critical layer/ligament thickness and its dependence on the network density can be explained by the previously introduced energy-based model or, alternatively, by the detailed micromechanical analysis of the craze growth mechanism as proposed by Kramer.

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A new ionic diol, 1,2-dihydroxypropylphosphonic acid (DPPA), was synthesized from epibromohydrin and triethyl phosphite. DPPA was used subsequently as a chain extender diol in the two-step synthesis of polyurethane ionomers. Both DPPA and the polyurethane ionomers were characterized by Fouriertransform infra-red and 'H and 31p nuclear magnetic resonance spectroscopy. Thermal analysis by differential scanning calorimetry was performed on the ionomers.

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4-Carboxybenzaldehyde was condensed with cyanoacetic acid to afford 1-carboxy-4-(2-cyano-2- carboxyvinyl)benzene (1). Homopolyamides were prepared from the polycondensation of I with aromatic diamines utilizing triphenyl phosphite and pyridine as condensing agents. In addition, various copolyamides were prepared by reacting a mixture consisting of 1 and terephthalic acid with an aromatic diamine. The synthesized polyamides contained olefinic bonds and pendent cyano groups. The homopolyamides showed higher solubility in common solvents than did the reference polyamide prepared from terephthalic acid and an aromatic diamine. Their differential thermal analysis traces revealed that they softened between 200°C and 300°C. Upon curing at 300°C for 70 h, they yielded heat-resistant crosslinked polymers. The thermal stabilities of the cured polymers were correlated with the curing conditions and their composition. They displayed higher thermal stability than the reference polyamide and were stable up to 372-405°C in N2. Furthermore, they are noteworthy for their high char yield at 800°C, namely, 68-78% in N2 and 58-69% in air.

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Relationships between the microscopic structure (chemical composition and topology) and the macroscopic properties, especially the toughness, of well defined polymeric networks below Tg, were investigated. Model networks were prepared from a triisocyanate, i.e. tris(4-isocyanatophenyl)-thiophosphate (Desmodur RFE) and well defined polymeric diols, namely poly(propylene glycol)s (PPGs) of various molecular weights (425, 725, 1000, 2000, and 4000). The experimental equilibrium rubber moduli of the various Desmodur-PPG networks are in good agreement with those calculated by means of the theory of branching processes. These networks are therefore considered to behave as model polymeric networks. Toughness was measured as a function of the crosslink density at temperatures well below the T~. The model networks are surprisingly tough. A linear dependence of the critical stress intensity factor, K~c, on the strand density is observed. The size of the plastic zone is related to the maximum extensibility of the network chain. Other properties of the glassy state (e.g. glass modulus and yield stress) have only a very slight dependence on the crosslink density.

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We report here structural and photophysical studies on polyacetylene prepared by various precursor routes. We find that control of stereoregularity, molecular weight and molecular weight distribution of the precursor allows improvements in ordering parameters, such as molecular orientation and crystallographic order of the final polymer. The photophysical properties of polyacetylene also depend on the particular precursor preparation route. The peak in the n-n* absorption lies between 2.15 and 2.65eV, depending on the precursor; also, photoinduced metastable band-gap states vary in position, shape and strength.

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Segmented block copolymers of polyisobutylene (PIB) and poly(butylene terephthalate) (PBT) were made by condensation polymerization of ~,og-di-anhydride telechelic PIB, with 1,4-butanediol and dimethyl terephthalate. The inherent viscosity of the polymers was between 0.35 and 2.0 dl g- 1. The extractability of the polymers with hexane was studied. The thermal behaviour of these polymers was studied by differential scanning calorimetry and dynamic mechanical thermal analysis. PBT-b-PIB had a glass transition temperature of -62°C and a melting temperature of 200-220°C. A shear modulus was found which, at room temperature, increased from 0.4 to 900 MPa with increasing PBT content in the block copolymer. The degradation was followed by measuring the change of inherent viscosity during thermal and hydrolytic treatment. The PBT-b-PIB showed good resistance to thermal and hydrolytic degradation

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Two types of poly(vinyl chloride) (PVC) samples are studied by mechanical spectroscopy, namely (i) a commercially available PVC that is submitted to different heat treatments and (ii) the same PVC but slightly crosslinked in order to compare the effect of this chemical crosslinking with the effect of the physical crosslinking obtained after ageing at T> Tg. The comparison is made by means of a theoretical approach for the non-elastic deformation of polymers

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The synthesis of a new poly[aryl ether(ketone-co-sulfone)] proceeds through a chemical mechanism similar to that in the poly(ether ether ketone) and poly(ether sulfone) polymerizations. It is basically a nucleophilic substitution of a dihalogenated species by two alkaline bisphenates. This paper considers the possibility of the occurrence of some side reactions previously observed during the synthesis of poly(ether ether ketone), poly(ether ketone) or poly(ether sulfone). Unwanted nucleophilic substitutions either by phenates (transetherifications) or by fluoride or hydroxyl anions are considered. Their effectiveness during the copolymer synthesis is demonstrated by different techniques and their influence on the final sequence distribution in the chain is discussed

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The styrene-arsenic sulfide complex initiated radical copolymerization of acrylonitrile (AN) with chromium acrylate (CrA3) at 85 +0.1°C, using dimethylformamide (DMF) as an inert solvent, yields an alternating copolymer as evidenced by the reactivity ratios rt =0.18 and r2=0.03 (Mr =AN, M2 =CrAa). The kinetic equation for the system is Rpoc[As2Sa]°'5[AN]t'°[CrA3] L°. The value of the activation energy and the average value of k2/kt are 96.2 kJ mol- 1 and 1.0 x 10- 51 mol- t s- t, respectively. The properties of the resulting copolymer were studied in the form of films. Nitric acid was strongly absorbed by these films, while the absorption of hydrochloric acid was comparatively low.

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The sorption properties of CO2 in several side-chain liquid crystalline polymers (side-chain LCPs) with various mesophases have been investigated. The equilibrium concentrations of the sorbed CO2 were measured over a wide temperature range, covering the whole of the phase states of the side-chain LCPs. The concentrations have been found to depend strongly on the phase state of the polymers. They increase significantly at the various phase transitions, i.e. crystalline to smectic, smectic to nematic, and liquid crystalline (smectic or nematic) to isotropic. A correlation between the solubility changes and the enthalpies of the transitions has been established.

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