1999 рік

The isochronal mechanical relaxation spectra of lightly cross-linked epoxidized natural rubbers (ENR) were measured at a frequency of 1 Hz and the results analyzed using the empirical Havriliak-Negami (HN) equation. The HN equation fitted the relaxation spectra very well. The fitting parameters, (Yand /3, obtained from the data fitting were used to interpret the relationship between molecular motions and structure of polymers based on the model proposed by Schonhals and Schlosser. Near the glass transition, the molecular motions of ENR in both the high and low frequency regions were not influenced by the level of cross-linking due to the low cross-linking density. Comparing with the natural rubber (NR), the epoxide groups of ENR promoted steric interactions and enhanced the inter-molecular cooperative motion. The activation energy of molecular motions for ENR was larger than observed for NR. The values of a! and o/3 of ENR were less than observed for NR. According to the model proposed by Schonhals and Schlosser, alp was correlated with the local intra-molecular motions and 01was correlated with the inter-molecular motions. The results suggest that the epoxide groups broaden the intra- and inter-molecular relaxation dispersion.

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Poly[4-amino-2,6-pyrimidinodithiocarbamate] (PPT) is prepared from the reaction of 2-mercapto-4,6-diaminopyrimidine with carbon disulfide followed by condensation through the removal of H 2S gas. The polymer is then used as a ligand to form polymer–metal complexes with the 3d-elements Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II). The DC electrical conductivity as a function of temperature is measured in the temperature range 300–500 K. The mechanism of conduction, the role of adsorbed water and complexation are explained on an energy diagram. This is carried out in accordance with the u.v.–VIS spectrum, TGA and DTA measurements. For comparison with 5d-elements, measurements are carried out also on Hg(II)–polymer complex.

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Studies examining the structure of monolayers formed by polymer chains grafted to a surface typically focus on chains attached at one end (tails). Bond fluctuation simulations are performed here to probe monolayers composed of equimolar mixtures of tails and double-grafted loops in which the looped chain length (Nloop) is varied at constant surface density and tail length (Ntail). Loops force the tails to adopt an extended trajectory normal to the surface, resulting in monolayer stratification. As Nloop increases, the height of the tail sublayer increases to a maximum, and then decreases to converge with the loop sublayer as Nloop ! 2Ntail. These results are compared to predictions from a selfconsistent field theory for bidisperse mixtures of grafted tails.

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of a seven-ring model for the crystalline polyetherketone known as 'PK99’, has been determined by single crystal X-ray The central benzene-1,3-dicarbonyl group in this oligomer adopts an 'open’ conformation, approximately in agreement with that proposed earlier for PK99 on the basis of X-ray powder and fibre diffraction data. The present oligomer structure (and a polymer structure simulated by extrapolation from the oligomer) do not, however, require the benzene-1,3-dicarbonyl group to adopt the previously assumed coplanar conformation. A single crystal X-ray study of a cyclic ether-ketone oligomer, also based on the benzene-1,3-dicarbonyl unit, demonstrates the potential of this group to act as a site for sharply re-entrant chain-folding.

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The formation of coordination complexes between the nitrogen lone pair on poly(4-vinylpyridine) and the metal center in dichlorotricarbonylruthenium(II) is described in this research contribution. {RuCl 2(CO) 3} 2 was chosen because octahedral d 6 heavy-metal centers with p-acid carbonyl ligands exhibit very large ligand field stabilization energies which enhance the glass transition temperatures of polymeric coordination complexes. Relative to undiluted poly(4-vinylpyridine), which exhibits a glass transition at 145°C, T g increases by 27°C at 3 mol% Ru 2þ. When the concentration of Ru 2þ is greater than 5 mol%, detection of a diffuse T g above 200°C is difficult via calorimetry because the discontinuity in specific heat decreases considerably. Ambient-temperature infrared spectroscopic data for the pyridine sidegroup in the polymer suggest that the pyridine nitrogen coordinates to ruthenium. Symmetry considerations and high-temperature infrared data for the carbonyl stretching vibrations are consistent with structural models which contain two CO ligands and two pyridine sidegroups or three CO ligands and 1 pyridine sidegroup in the coordination sphere of ruthenium. Hence, it is possible that the transition-metal salt bridges two different chains via the pyridine nitrogen lone pair, forming coordination crosslinks. Hindered mobility of this nature provides a reasonable explanation for the enhancement in T g by 9°C/mol% Ru 2þ, up to 3 mol% Ru 2þ. Ambient temperature infrared signals in the carbonyl region suggest that as many as five different ligand arrangements of the following pseudo-octahedral complex, RuCl 2(CO) 2(Py) 2, exist simultaneously at low Ru 2þ concentrations and could be responsible for coordination crosslinks. Upon heating, the highly symmetric isomers with trans-CO ligands transform irreversibly to pseudo-octahedral structures with lower symmetry (i.e., cis-CO ligands). Octahedral ruthenium d 6 salts are attractive physical property modifiers when polymeric ligands coordinate to the metal center.

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Poly(2-trimethylsilyl-2-propyl methacrylate-co- g -butyrolactone-2-yl methacrylate) was synthesized and evaluated as a chemically amplified resist for ArF lithography. The polymer has excellent transmittance at 248 nm and also has a good transmittance at 193 nm. In addition, the polymer possesses good thermal stability up to 2008C, whereas in the presence of an acid the cleavage of the 2-trimethylsilyl-2-propyl ester group begins at about 808C in a catalytic manner. Patterns of 0.24 mm line/space were obtained with a conventional developer, 2.38 wt.% tetramethylammonium hydroxide aqueous solution, using an ArF excimer laser exposure system.

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The ratio of the unperturbed mean-square end-to-end distance to the molecular weight in the random-coil limit, ((R2)0f/m) in the freerotation approximation was calculated for chains of linear polyurethanes PUR-DI: prepared from 4,4’-methylenediphenyl diisocyanates and low-molecular-weight diols HO-(CH2)k-OH (k = 2, 3, 4 and 6). It was found that the experimental values of (R2)0f/m), estimated in the previous paper are very close to the values of (R2)0f/m), calculated under the assumption that the groups of bonds CH2-C&-NH NH-CO-0-CH2 can be replaced by rigid virtual bonds.

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We have derived a generalized equation for correlating the morphological parameters (matrix ligament thickness, particle spatial distribution parameter, mean particle size, particle size distribution and particle volume fraction) of polymer blends with particles obeying the log-normal size distribution. The particle spatial distribution parameters for eight regular lattices and three actual morphologies have been calculated. The particle spatial distribution parameter for the morphology of well-dispersed particles is between 1 and ca. 1.2, and is larger than those for the pseudonetwork morphology and the morphology of agglomerated particles. The relationships between the particle spatial distribution parameters defined in this work and those given in the literature are discussed.

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A new transamidation reaction, between an aliphatic secondary amide and an aromatic nitrile, leading to an aromatic amide and an aliphatic nitrile is described in this article. The best conditions have been established: 3008C, no solvent, 2 h, 1 wt.% PPA as catalyst. Yields were found to be independent of the nature of para substituents, but strongly decrease for an ortho substituted compound. NMR studies support the mechanisms such as hydration of the nitrile, amidolysis, dehydration of the aliphatic amide leading to the aromatic amide and the aliphatic nitrile.

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Several aromatic 1,3,4-oxadiazole derivatives have been investigated as thermal stabilizers for rigid poly(viny1 chloride) (PVC) at 180°C in air. Their stabilizing efficiencies are evaluated by measuring the rate of dehydrochlorination and the extent of discoloration of the degraded polymer. The results obtained show the greater stabilizing efficiency of the investigated compounds as compared with dibasic lead carbonate (DBLC), barium-cadmium-zinc stearate (Ba-Cd-Zn stearate) and n-octyltin mercaptide (n-OTM), which are commonly used industrial stabilizers. Their higher efficiencies are indicated not only by their longer induction periods during which no detectable amounts of hydrogen chloride gas are liberated, but also by their lower dehydrochlorination rates during the subsequent stages of degradation. The stabilizing efficiency of these compounds is influenced by the number of the 1,3,4-oxadiazole rings as well as by the introduction of electron donating substituents in the phenyl ring of the stabilizer molecule. This can be attributed to the replacement of the labile chlorine atoms on the polymer chains by more stable groups derived from the stabilizer. This substitution reaction proceeds most probably through an ionic mechanism. Moreover, stabilization with the investigated compounds results in an improvement in the extent of discoloration of the degraded PVC relative to the reference stabilizers. This may be attributed to the ability of these compounds to disrupt the formation of the conjugated double bonds which are responsible for discoloration. Combination of the investigated compounds with industrial stabilizers greatly improves the stabilizer of 3: 1. This synergism occurs stabilizing efficiency which reaches its maximum at a molar ratio of oxadiazole stabilizer/reference due to the interaction between the residual investigated stabilizers with the reference metallic stabilizers’ by-products, metal chlorides, thus protecting the polymer from the deleterious effect of these chlorides that accumulate when the metallic stabilizers are used alone.

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