1999 рік

A novel type of poly(urethane–imide) was prepared by a reaction of a polyurethane prepolymer and a soluble polyimide containing hydroxyl functional group. Polyurethane prepolymer was prepared by a reaction of polyester polyol and 2,4-tolylenediisocyanate and then end-capped with phenol. Soluble polyimide was prepared by the two-step synthesis from 2,2 0 -bis (3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3 0 -diamino-4,4 0 -dihydroxybiphenyl (AHBP). Soluble polyimides having various content of hydroxyl functional groups were prepared similarly by using diamine mixtures of AHBP and oxydianiline. Cast films were obtained from blend solutions of the polyurethane prepolymer and the polyimide. The cast films were thermally treated at various temperatures to give a series of transparent poly(urethane–imide) films. By changing the ratio of polyurethane and polyimide components, poly(urethane–imide) films having various properties from plastic to elastomer were prepared. Dynamic mechanical analysis showed that lower glass transition temperature (Tg) of the films shift to high temperature with the increase of polyimide component, suggesting that the two polymer components are miscible to some extent. Thermogravimetric analyses indicated that the thermal degradation of poly(urethane–imide) occurs at ca. 2708C, which is ca. 308C higher than the conventional polyurethane, confirming that the introduction of polyimide component improved the thermal stability of polyurethane.

Детальніше...  

7Li nuclear magnetic resonance (n.m.r.) spectra obtained in static mode were used to characterize blends of polyamide-6 (PA6) and lithium sulfonated polystyrene ionomers (LiSPS) with 5.4 and 9.7 mol% sulfonate groups; for the blends with the higher degree of sulfonation a linear relation was found between full n.m.r. line width at half-maximum (PWHM) and the glass transition temperature (T,, as determined by differential scanning calorimetry, d.s.c.). Magic angle spinning (MAS) spectra were also recorded and it was shown, in particular, that the line width of the central transition provides information on polymer miscibility on a scale smaller than 2 nm. Based on simulations of the 'Li spectral data, it is suggested that three lithium species are present, whose concentration is determined by the sulfonated polystyrene/PA6 ratio in the blend; the miscibility of the blend is shown to be mainly correlated with one of the species.

Детальніше...  

Blend films of poly(ε-caprolactone) (PCL) and poly(dl-lactide) (PDLLA) with 0.5 weight fraction of PCL were prepared by means of solution casting and their degradation behavior was studied in phosphate buffer solution containing Pseudomonas (PS) lipase. Enzymatic degradation of the blend films occurred continuously within the first 6 days and finally stopped when the film weight loss reached 50%, showing that only PCL in the blends degraded under the action of PS lipase in the buffer solution. These results indicate the selectivity of PS lipase on the promotion of degradation for PCL and PDLLA. The thermal properties and morphology of the blend films were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and scanning electron microscopy (SEM). The morphology resulting from aggregate structures of PCL in the blends was destroyed in the enzymatic degradation process, as observed by SEM. These results confirm again the enzymatic degradation of PCL in the blends in the presence of PS lipase.

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A series of water-soluble pendent oligo(ethylene glycol)-based statistical copolymers and terpolymers were synthesised using group transfer polymerisation (GTP). More specifically, oligo(ethylene glycol) monomethyl ether monomethacrylate (OEGMA) macromonomers containing 6, 21 or 44 ethylene glycol units were copolymerised with either benzyl methacrylate (BzMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA) or tetrahydropyranyl methacrylate (THPMA) to give statistical copolymers. The analogous terpolymers were obtained by copolymerising the oligo(ethylene glycol) monomethyl ether monomethacrylates with n-butyl methacrylate (nBuMA) and either BzMA or DMAEMA. Gel permeation chromatography was used to determine copolymer molecular weights and polydispersities, while proton NMR spectroscopy was used to assess their compositions. In all cases, the final copolymers were near-monodisperse (Mw/Mn’s , 1.2) and good molecular weight control was achieved. The BzMA-containing copolymers were deprotected via catalytic hydrogenolysis to selectively remove the benzyl groups, giving polymers containing carboxylic acid groups. Similarly, the THPMA-containing polymers were deprotected by acidic hydrolysis to remove the tetrahydropyranyl groups, also resulting in acidic statistical polymers. Comparison of the degrees of deprotection achieved using the BzMA and THPMA protected monomers suggests that THP is the preferred protecting group since it is removed quantitatively regardless of the copolymer composition. In contrast, incomplete deprotection was obtained for the copolymers containing more than 67 mol% BzMA.

Детальніше...  

Polyurethanes prepared from 1,6-diisocyanate hexane (HDI) and 2,4-tolylene diisocyanate (2,4-TDI) with liquid crystalline chain extender 4,4’-bis(n-hydroxyalkyloxy)biphenyl (n-PBP, n = 2, 3, 6) were reported. Characterizations of monomers and polymers were performed by infrared spectroscopy (IR), 'H-NMR, solid-state C13-NMR, and elemental analysis. The phase transition behaviors of polyurethanes were investigated by Global TSC, DSC, and polarized microscopy (POM). Our results showed that monomers 4,4’-bis(n-hydroxyalkyloxy) biphenyl exhibit smectic type mesophase. It was observed that the longer the spacer length of polyurethanes, the higher the chain mobility, the larger DOD (degree of disorder) value and the lower the relaxation time. Also the phase transition temperature of polyurethanes decreases with increasing spacer length. DSC measurements and texture observations indicated that H2, H3, H6 and T6 exist in both mesophase and crystal phase. Quantitative analysis of temperature dependence hydrogen bonding revealed that hydrogen bonded content (Xb) of the C=O group for all samples decreased with increasing temperature. For the H series, both Xb and AH decrease with increasing spacer length of the mesogenic diol.

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A C 60 derivative, benzylaminofullerene (BZAF) with a stoichiometry of [C 60H 1.9(NHC 6H 5) 1.9] was synthesized by nucleophilic addition of fullerene with benzylamine in DMSO/o-dichlorobenzene. Free radical copolymerization of BZAF with methyl methacrylate or ethyl methacrylate gave high yields of copolymers. The optical limiting threshold of BZAF is comparable with that of C 60 and stronger than those of the copolymers.

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The carbonyl groups in eight high-performance polyaryl-etherketones and -thioetherketones were reduced to methylene linkages in high yield by treatment at room temperature with triethylsilane in a mixture of trifluoroacetic acid or methanesulphonic acid with either dichloromethane or chloroform. When the starting polyketone is readily-crystallizable, the reduced polymer also tends to crystallize during workup. Amorphous polyketones likewise give amorphous reduction products. The methylene-bridged polymers in general have significantly lower melting points and/or glass transition temperatures than their parent polyketones.

Детальніше...  

Phenylacetylene (PA) and 1-hexyne (HX) were copolymerized in solution using two kinds of Ziegler-Natta catalysts, Ti(On-Bu),-AlEts and Fe(acac)s-AlEt,, in toluene and by metathesis with the WC16-Ph$n initiating system in toluene and 1, 4-dioxan. The compositions of copolymers, obtained under various monomer charge ratios in the range of 5-95 mol% of PA or HX, were determined from their 200 MHz 'H n.m.r. spectra. The experimental data processed according to the Kelen-Ttidos approach and, for comparison, by using a non-linear least squares curve-fitting procedure indicated that, for the four investigated systems, the copolymerization process of the PA/HX-pair can be adequately described by the terminal-unit model. The reactivity ratio values calculated from both methods were the same. Based on these findings, the relative reactivity of two acetylenic monomers was discussed. Interestingly, the results obtained with the Ziegler-Natta catalysts showed that the propagation step mechanisms changed greatly not only with the type of transition metal compound [Ti(On-Bu)4 and Fe(acac)J, but also with the chemical nature of ligands bonded to transition metal [Fe(acac)s and Fe(propionate)s]. On the other hand, the reaction promoted by W-containing metathesis initiator was found to be strongly dependent on the polymerization solvent. The numberaverage molecular weights of copolymer samples and the number-average sequence lengths of PA and HX-units were also reported.

Детальніше...  

The rheological characteristics of a particle-suspended Boger fluid are reported. Non-shear thinning, highly elastic polymer solutions were obtained from a mixture of high-molecular-weight polyisobutylene (PIB) and low-molecular-weight polybutene (PB). Kaolinite was chosen as the suspended particles. The shear viscosity and first normal stress difference of the kaolinite-suspended PIB/PB solution exhibit characteristics similar to those of Boger fluids. In contrast to polymer melts with nearly spherical particles, the elasticity of this system increases with the addition of particles, and a qualitative interpretation based on PB (the solvent) as a 'shielding’ agent is given.

Детальніше...  

In 1964 Kovacs (Kovacs, AJ, Transition vitreuse dans les polymères amorphes. Etude phénoménologique. Fortschr Hochpolym-Forsch 1964;3:394–507) published a paper in which he analyzed structural (volume) recovery data in asymmetry of approach experiments. Kovacs 21 used a parameter referred to as t -effective (t eff) which is defined in terms of the volume departure from equilibrium d as t eff ˆ 2 1/d dd /dt. In plots of the log(1/t eff) vs. d Kovacs observed an apparent paradox in that the values of t eff did not converge to the same point as d approached zero (i.e. equilibrium). Hence the equilibrium mobility of the structural recovery seemed path dependent. Also, the apparent paradox was accompanied by a spreading of the curves for t eff in the up-jump experiments which has come to be known as the expansion gap. While it is currently accepted that the paradox itself does not exist because the curves will converge if the measurements are made closer to d ˆ 0 (Kovacs’ estimates of t eff were made for values as small as d < 1.6 × 10 24), the existence of the expansion gap is still a subject of dispute. This is particularly relevant today because recent models of structural recovery have claimed 'success’ specifically because the expansion gap was predicted. Here we take the data Kovacs published in 1964, unpublished data from his notebooks taken at the same time, as well as more recent data obtained at the Institut Charles Sadron under his tutelage in the late 1960s and early 1980s. We then examine them using several different statistical analyses to test the following hypothesis: the value of t eff as ud u ! 1.6 × 10 24 for a temperature jump from Ti to T0 is significantly different from the value obtained for the temperature jump from Tj to T0. The temperatures Ti or Tj can be either greater or less than T0. If the hypothesis is rejected, the t eff-paradox and expansion gap need to be rethought. If the hypothesis is accepted, then the argument that reproduction of the expansion gap is an important test of structural recovery models is strengthened. Our analysis leads to the conclusion that the extensive set of data obtained at 408C support the existence of an expansion gap, hence an apparently paradoxical value of t eff, for values of ud u $ 1.6 × 10 24. However, at smaller values of ud u it appears that the values of t eff are no longer statistically different and, in fact, the data suggest that as ud u ! 0 all of the t eff values converge. In addition, data for experiments at 358C do not have sufficient accuracy to support the expansion gap for such small values of ud u because the duration of the experiments is significantly longer than those at 408C. Consequently the data readings taken at 358C were made at longer time intervals and this leads to dramatically reduced error correlations.

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