1999 рік

Alginate is an attractive material for controlled drug delivery and cell transplantation applications. However, alginate hydrogels are not degradable, have limited mechanical properties, and lack the functional groups required for cell interaction. To address these limitations of alginate while maintaining their favorable characteristics, we have synthesized new polymers derived from sodium poly(guluronate), the portion of the alginate molecule that is responsible for its gelling behaviour. Sodium poly(guluronate) was isolated, oxidized with sodium periodate, and cross-linked with adipic dihydrazide to yield hydrogels with a wide range of mechanical properties, and with cell adhesion peptides coupled to their backbones.

Детальніше...  

The complete phase diagram of the poly(ethylene oxide)/lithium trifluoromethane sulfonate polymer electrolyte was determined by combined X-ray diffraction and differential scanning calorimetry. The sample preparation has dramatic effects on morphology and consequently on the phase diagram. The existence of three different molecular adducts involving the polymer and the salt was deduced from the phase diagram. These adducts transform into each other by peritectic reactions. Moreover, two different forms of pure lithium trifluoromethane sulfonate were observed. This polymorphism was studied by X-ray diffraction and differential scanning calorimetry. It was demonstrated that this salt undergoes a transition to a phase of higher symmetry at 1798C. An orthorhombic unit cell (a ˆ 1.496 nm, b ˆ 1.475 nm, c ˆ 1.425 nm) was proposed for the high temperature form of the salt.

Детальніше...  

A series of N-(substituted phenyl) maleimides was synthesized and their free radical chain polymerization examined. Polymerization of the N-(hydroxyphenyl) maleimides in DMF gave typically very low molecular weight polymers. Masking the phenolic functionality with an acetoxy group gave marginally higher molecular weights. Protection using a tetrahydropyranyl (THP) substituent gave a similar polymerization pattern to acetoxy. However, the THP protected monomers had increased solubility in non-polar solvents such as benzene, and when polymerized in this solvent gave very much higher molecular weight polymers. The reactivity of the maleimide monomers was also found to be dependent on the substitution pattern of the phenyl ring, with substituents in the ortho position tending to lower the molecular weight of the polymer formed. The THP substituent was readily removed to yield poly(N-(hydroxyphenyl) maleimides). The polymers were found to exhibit excellent thermal stability.

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We demonstrate that the interfacial tension between two molten polymers can be reduced significantly by the formation of graft copolymer at the interface by chemical reaction. If the grafting chains are short enough, the interface becomes unstable and roughens markedly, leading even to the formation of a polymer microemulsion. We investigate the onset of this roughening instability and find it that can be predicted satisfactorily by self-consistent mean field theory.

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Two samples of a single composition blend of PET and PEN were prepared by solution blending using different solvents such that the hydroxyl end groups in one blend were modified. The rate of transesterification in each blend was studied using proton NMR, an established technique for this system. The results indicate that the rate of transesterification is influenced dramatically by end group modification, providing clear evidence that hydroxyl end groups participate in the reaction mechanism.

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The main point of interest when discussing lubrication is to understand what lubricants do in a compound, particularly during processing. Among lubricants, we can find metal soaps, which are often heat stabilizers of PVC. In order to study the influence of lubricants on the flow properties, it is of particular interest to analyse the behaviour of the material at the die walls, where slip may be observed. Then, in the present paper, the lubricating ability of a lead stabilizer during extrusion of a plasticized PVC formulation was investigated through an instrumented die, which allowed us to have the apparent flow properties at the wall. Rough and smooth surfaces of the die were used in order to prevent or promote slip at the metal surface. From this method, it was possible to observe the slip phenomenon above a critical concentration, whereas the analysis of the die surface through SEM coupled energy dispersive x-ray spectroscopy shows that lead stabilizer migrates even at low concentration. So, slip occurs when the lubricant layer forms a continuous solid layer which modifies the polymer–metal interface properties.

Детальніше...  

Eudragit E, a copolymer of N,N-dimethylaminoethyl methacrylate and neutral methacrylic acid esters, has been found to form sixmembered cyclic anhydrides via intramolecular ester condensation by a heating process only, without adding any catalyst or initiator. A novel reflectance Fourier transform infrared microspectroscopy system equipped with differential scanning calorimetry (FTIR/DSC) was used to determine the thermal-dependent anhydride formation of Eudragit E film. The anhydride-related IR peaks at 1801, 1763 and 1007 cm -¹ appeared from 180°C and increased with the heating temperature, while the peaks at 2820 and 2770 cm -¹ for the dimethylamino group reduced gradually with the increase of temperature, strongly suggesting that the anhydride formation by ester condensation started above 180°C. The appearance of peaks at 1801 and 1763 cm -¹ not only illustrates the asymmetric and symmetric stretching vibration mode of the carbonyl group existing in the anhydride structure, but also exhibits the formation of six-membered cyclic anhydrides during the heating process. Moreover, the higher peak intensity ratio of 1763 cm -¹/1801 cm -¹ also reveals the predominant role of intramolecular ester condensation in anhydride formation in Eudragit E film.

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The orientation-induced conformational transition was studied on thin films of poly(methylhexylsilane) (PMHS). The orientation behavior of molecular chains was analyzed by the inclination-angle-dependence of the polarized UV spectrum and the FTIR reflection–absorption spectroscopy (RAS). The changes in conformation of PMHS chains were monitored with the UV absorption spectrum. It was shown that the structure of the spin-cast film depended upon the thickness of films. In thick film (408 nm), molecular chains are not oriented, and favor the disordered conformation, which shows absorption band at 300 nm. In contrast, extended conformation with trans-rich segments is produced in addition to the disordered conformation in thin spin-cast films (45–100 nm). The extended conformation gives rise to a sharp absorption band at 338 nm. The molecular chains with extended conformation are oriented parallel to the substrate surface. The uniaxially oriented films were prepared by drawing the film on supporting polymeric substrates and by crystallization on highly oriented polymer films. As the degree of orientation is increased, the 338 nm band increases in intensity relative to the 300 nm band. The 338 nm band dominated the UV spectrum of the highly oriented PMHS film instead of the 300 nm band. A conformational transition to the extended conformation from disordered state is induced by the molecular orientation, exhibiting a drastic spectral change in the UV spectrum.

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The effects of different molecular weight distribution of (methylmethacrylate N-phenylmaleimide) copolymers of various molecular weights and their blends on the melt flow index, the storage and loss modulus, and the zero shear viscosity are investigated. Copolymers with higher N-phenylmaleimide contents and definite molecular structure show a typical thermal stability shown by their rheological properties. These studies seem to be useful for first estimations in screening tests and production control.

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This communication presents results from dynamic mechanical analysis and measurement of charge-recombination luminescence showing that the vitrification process during isothermal cure of an acrylate resin appears to proceed in two steps. Glass formation, as determined by charge-recombination luminescence, is found to occur much before macroscopical gelation and vitrification are detected in dynamic mechanical analysis. This suggests the presence of a micro-vitrification transition in addition to the analogous micro-gelation process which has been reported in diacrylate polymerisations.

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