1999 рік

Water and solute or drug transport in crosslinked polymeric materials was investigated to determine the effects of polymer morphology, composition and solute properties on transport behavior. Two crosslinked polymer systems, poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (P(HEMA-co-MMA)) and poly(vinyl alcohol) (PVA), were used in water transport and solute release experiments. Structural parameters of the polymers investigated in this work included the initial polymer molecular weight, the nominal crosslinking ratio, and the copolymer composition. Swelling rates, water diffusion coefficients and the diffusional Deborah number, De, were used to characterize the water uptake process. Swelling rates correlated well with the polymer network mesh sizes; the slowest rate of water uptake was observed in P(HEMA-co-MMA) samples containing large quantities of methyl methacrylate. Initial crosslinking ratios had a sizable effect on water uptake in crosslinked PVA samples but not in the P(HEMA-co-MMA) polymers. Drug release rates, drug diffusion coefficients and the swelling interface number, Sw, were used to characterize solute transport. Release experiments were conducted using eight solutes: theophylline, triamterene, oxprenolol HCl, buflomedil HCl, vitamin B 12, dextran, inulin and myoglobin. Release rates decreased with increasing solute molecular weight. A molecular weight cut-off, beyond which drug release was greatly hindered by the hydrogel mesh size, was established for each polymer tested.

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Gas separation membrane permselectivity is often improved by the introduction of stiffer polymeric backbone structures. This chain rigidity enables the polymeric segments to discriminate more selectively between penetrants of different size. Although not extensively reported in the literature, ladder and semi-ladder polymers formed from tetraamines and dianhydrides potentially provide rigid polymeric structures void of significant rotational mobility. This work examines the gas transport and sorption properties of BBL, a ladder polymer synthesized from 1,2,4,5-tetraaminobenzene tetrahydrochloride and 1,4,5,8-naphthalenetetracarboxylic acid. In addition, the behavior of He, CO2, O2, N2, and CH4 permeability, diffusion, and sorption coefficients with temperature is examined and shown to follow the Arrhenius and van’t Hoff relationships. The near-ambient permeation properties of BBL are also compared with other previously reported semi-ladder polymers formed using polypyrrolone chemistry. These semi-ladder polymers incorporate both flat, packable monomers such as those used to form BBL as well as bulky monomers to inhibit chain packing.

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Surface properties of two polyethers containing pyridine and pyrazine units, respectively, were compared with polysulfone. The polymers were investigated by inverse gas chromatography. The dispersive contributions of the surface free energy and the K A and K B parameters expressing the ability of the stationary phase to act as Lewis acid or Lewis base were calculated. It was shown that the polymer with pyridine units possessed extraordinarily high K B values whereas the polysulfone showed amphoteric behaviour with predominant Lewis basicity.

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The effect of adding diblock copolymer poly(styrene-b-4-vinylpyridine) (P(S-b-4VPy), to immiscible blends of syndiotactic polystyrene (sPS)/thermoplastic polyurethane (TPU) on the morphology, thermal transition, crystalline structure, and rheological and mechanical properties of the blends has been investigated. The diblock copolymer was synthesized by sequential anionic copolymerization and was melt-blended with sPS and TPU. Scanning electron microscopy (SEM) showed that the added block copolymer reduced the domain size of the dispersed phase in the blends. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the extent of compatibility between sPS and TPU affected the crystallization of the sPS in the blends. Tensile strength and elongation at break increased, while the dynamic modulus and complex viscosity decreased with the amount of P(S-b-4VPy) in the blend. The compatibilizing effect of the diblock copolymer is the result of its location at the interface between the sPS and the TPU phases and penetration of the blocks into the corresponding phases, i.e. the polystyrene block enters the noncrystalline regions of the sPS, and the poly(4-vinylpyridine) block interacts with TPU through intermolecular hydrogen bonding.

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In this article, a phosphorus containing bismaleimide (V) based on 2-(6-oxido-6H-dibenz kc,el k1,2l6-yl)-1,4-dihydroxy phenylene (I) was synthesized and copolymerized with 4,4 0 -bismaleimidodiphenylmethane (BMDM) in various weight ratio (0–33 phr). DSC scans show that the introduction of V into BMDM has increased the processing window for the resulted copoly(bismaleimide). DMA scans show these cured BMIs exhibit good modulus ( , 2 GPa) up to 4008C. There is no tangent peak for these cured BMIs implying that there is no relaxation below 4008C. TMA scans show introduction of V into BMDM increase the coefficient of thermal expansion (CTE). However, CTE of these cured BMIs are less than 50 ppm, which is much less than common epoxy. There is no second transition during TMA heating scans up to 4408C, so Tgs of these cured BMIs are higher than 4408C, which is consistent with the DMA measurement. TGA heating scans also indicate that they have high thermal stability and their char yields increase with the content of V. Char yields at 8008C shift from 48 to 63 in nitrogen and from 0 to 18 in air when 25 phr of V was introduced into BMDM. TGA isothermal experiments show that these cured BMIs are thermally more stable in air than in nitrogen below 4508C. Char yields also increase with the content of V.

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Deuterium n.m.r. is used to observe the change in segmental dynamics and orientation at the crystallization temperature T c in a uniaxially stretched poly(dimethylsiloxane) (PDMS) network. Experiments are performed over a wide temperature range (235–294 K). The amorphous parts of the chains are probed via perdeuterated n-octane probe molecules dissolved in the network. 2H n.m.r. spectra change drastically within a small temperature interval of 4 K in the vicinity of T c. Above T c, the spectra reflect the uniaxial dynamics of the octane probes. In the vicinity of T c, the spectra are sensitive to the internal dynamics of the octane probe and indicate a heterogeneity in the mobility of the network chains. The isotropic lines obtained for T ⱕ T c confirm that the local constraints introduced by the external deformation disappear in the amorphous part of the sample in the presence of the crystalline phase.

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Three compositionally different copolymers derived from N-vinylcarbazole and N-phenyl-2-(5⬘-vinyl-2⬘-thienyl)-5-(2⬙-thienyl)-pyrrole were synthesised chemically and characterised. The composition of the copolymers was estimated using FT-IR spectroscopy and in situ spectroelectrochemistry and spectrocolorimetric measurements were performed on the solid state electrochromic devices fabricated using these copolymers as working electrodes. The colour contrasts of these devices in both the neutral and the doped states were measured by spectrocolorimetry conforming to the Commission International de l’Eclairage (CIE) methods. The CIE colour coordinate values in the pdoped state of the devices could be correlated to the comonomer ratios in these copolymers.

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Reactive diluents for cationic cycloaliphatic epoxide UV coatings were synthesized using caprolactone polyols and tetraethyl orthosilicate (TEOS). The structures of the TEOS functionalized polyols were characterized using IR, 1H-NMR, 29Si-NMR, and ESI-FTMS spectroscopy. The resulting siloxane functionalized polyols were used to formulate cationic UV coatings with 3, 4-epoxycyclohexylmethyl-3, 4-epoxycyclohexane carboxylate (a cycloaliphatic diepoxide). The crosslinking reactions were monitored using IR and 29Si-NMR spectroscopy. The cured films were evaluated in terms of tensile properties and glass transition temperature. The resultant coatings showed greater tensile modulus, lower elongation, and higher glass transition temperature. In addition, the siloxane functionalized polyols also effectively reduced the viscosity of the coatings formulations. Based on the curing behaviors and spectroscopic data, possible crosslinking reaction(s) were postulated.

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Polypyrrole films containing different dopant ions were electrochemically synthesized and the interaction between polypyrrole and water was evaluated by means of sorption isotherm, cluster function and d.s.c. It was found that the water sorbed in the polypyrrole behaved as a non-freezing bound water which was rather isolated and prevented from clustering over the whole experimental range of the relative water vapour pressure from 0.1 to 0.95. This might be associated with the nature of the conductive polymers having a p-conjugated system where the delocalization of carbonium charges would lower the ionic polarity and hydrophilicity of the polymeric chains.

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After thermal poling, pyroelectricity and a pronounced dielectric hysteresis have been observed on films of a poly(vinyl alcohol) with azobenzene-alkoxy side chains (Az-PVA). Based on dielectric spectroscopy data and structural information from differential thermal analysis, the pyroelectricity can be explained with reversible dipole–density changes during thermal expansion, whereas the dielectric hysteresis is proposed to result from the polarisation caused by charge carriers, probably ions. These findings are also significant for the interpretation of dielectric hysteresis measurements on other polymer-electret materials.

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