Cyclo dehydration reaction of polyhydrazides. II. Kinetic parameters obtained from isothermal thermogravimetry

The kinetics of the thermal conversion reaction of poly-(1,3-phenyl-1,4-phenyl)-hydrazide into poly-(1,3-phenyl-1,4-phenyl)-1,3,4-oxadiazole have been studied with isothermal thermogravimetry in continuation of a study with nonisothermal thermogravimetry described in a previous paper. Although the isothermal measurements are much more time-consuming, they provide some new information and insight about the cyclo dehydration reaction of the polyhydrazide. The physical state of the sample, rubbery or glassy, seems to influence the kinetics considerably. The kinetic parameters determined with the isothermal method for the polymer in its glassy state agree well with the parameters derived from the previously reported nonisothermal measurements, while the kinetic parameters for the expected rubbery state differ considerably. The morphological state or the history of the polymer has also a considerable influence on the kinetics of the isothermal conversion process. The powder form of the polymer has a much lower isothermal conversion rate than the film form

Gas separation properties of a thermally stable and chemically resistant polytriazole membrane

The polymer poly (1,3-phenyl-1,4-phenyl)-4-phenyl-1,3,4-triazole has been investigated for its gas separation properties. This thermally stable and chemically resistant polymer can be processed into membranes by the phase-inversion technique because of its unexpectedly good solubility in formic acid. Homogeneous membranes have been tested with respect to their permeability for several gases, and the influence of time and temperature upon permeation has been investigated. The polymer shows reasonable permeabilities for several gases and excellent selectivities. After a conditioning time of several days in which the permeability of the faster-moving gases increases by a factor of about 2, the permeation properties of the polymer remain constant for at least two months. A thermal treatment at 295°C, just above the glass transition temperature, can reduce the conditioning time and can prevent the film from shrinkage at high permeation temperatures without affecting the permeation properties

Cyclo dehydration reaction of polyhydrazides. I. Kinetic parameters obtained with nonisothermal thermogravimetry

The thermal conversion reaction of poly-(1,3-phenyl-1,4-phenyl)-hydrazide into poly-(1,3-phenyl-1,4-phenyl)-1,3,4-oxadiazole has been studied using thermogravimetry (TG). For the evaluation of the energie of activation and other kinetic parameters of this cyclo dehydration reaction a method developed by Ozawa was used, where polymer samples are heated with different constant heating rates. With this method the energy of activation can be determined accurately as a function of the degree of conversion. In this way a parallel reaction could be observed starting at the end of the nonisothermal conversion process. The polymer was used in two different morphological states, a powder and a film. A slightly higher energy of activation and a considerably higher pre-exponential factor were observed for the film indicating a dependency of the kinetics on the morphological state or on the history of the polymer sample

Thermal behavior of polytriazole films: a thermal analysis study

The thermal behavior of poly(1,3-phenyl-1,4-phenyl)-4-phenyl-1,2,4-triazole has been investigated using different scanning calorimetry (DSC) and thermogravimetry (TG). Processes are studied for this thermally stable polymer that take place between 200 and 500°C. While the polycondensation reaction product in powder from appeared to be partially crystalline, films prepared by casting from a formic acid solution appeared to be completely amorphous. A thermal treatment between Tg(~ 270°C) and Tm(~430°C) can introduce crystallinity in the films because of the polymer's ability to cold crystallize. The cold crystallization temperature Tc seems to be dependent on the preparation history of the solid polymer phase. Thermal annealing of the films just below Tg does not introduce crystallinity but inhibits subsequent cold crystallization at higher temperatures. Crystallization upon cooling from the crystalline melt has not been observed either. At temperatures just above the crystalline melting point the polymer starts to decompose in an exothermic reaction

Cyclodehydration reaction of polyhydrazides. III. Influence of the sample history

The influence of preparation history upon the thermal cyclodehydration reaction of polyhydrazide samples has been investigated. Solid polyhydrazide samples were prepared from DMSO solutions using the phase-inversion technique. Significant differences in conversion rates were observed between samples prepared by nonsolvent immersion precipitation and by evaporation of solvent. It appeared that contact with the nonsolvent water during the sample preparation process has considerable influence on the conversion rate. Not only does the immersion in and washing with water lead to a better removal of the solvent also the pH of the water determines the rate of conversion. A distinct change in the conversion rate is found for washing water at a pH of 7. Basic washing solutions showing lower conversion rates than acid ones. A mechanism explaining these phenomena is proposed

Protein separation using affinity binding. 1. Polystyrene core-shell latex as ligand carrier

Polystyrene core-shell latex particles are introduced as affinity ligand carriers for affinity separations. The particles, prepared by a seeded emulsion polymerisation process, are submicron in size and composed of a hard polystyrene core surrounded by a hydrophilic shell to which affinity ligands can be covalently coupled. The reactive dye Cibacron Blue is studied as model ligand. This dye ligand, which is covalently coupled directly to hydroxyl groups on the particle surface, is studied and the amount of coupled dye is determined quantitatively by diffuse reflection spectroscopy. The degree of coupling can be controlled by the ionic strength of the reaction medium. The adsorption of bovine serum albumin to the latices appears to be proportional to the ligand density. The functionalised core-shell latices show a high colloidal stability, fast protein adsorption/desorption kinetics and a low non-specific adsorption. The latex particles can find use in affinity separation techniques such as affinity chromatography and affinity membrane filtration