Apparent Activation Energy Of Degradation Research Articles

Kinetics of copolymerization and degradation of poly[acrylonitrile- co-(amino ethyl-2-methyl propenoate)

Amino ethyl-2-methyl propenoate was firstly used to successfully copolymerize with acrylonitrile in a H 2O/dimethylsulfoxide (DMSO) mixture between 50 °C and 70 °C under N 2 atmosphere. This was achieved by using azobisisobutyronitrile as the initiator. Kinetics of copolymerization of acrylonitrile with amino ethyl-2-methyl propenoate was investigated. The kinetic equation of copolymerization was obtained and the apparent activation energy of degradation of poly[acrylonitrile- co-(amino ethyl-2-methyl propenoate)] was determined. Increasing DMSO concentration in the solvent mixture leads to a rapid increase in the degradation apparent activation energy. The apparent activation energy decreases quickly with an increase in the comononer amino ethyl-2-methyl propenoate concentration, and such a change becomes less prominent as the molar ratio of amino ethyl-2-methyl propenoate/acrylonitrile goes beyond 2/100. The apparent activation energy also increases along with the copolymerization temperature. The resultant fibers prepared from poly[acrylonitrile- co-(amino ethyl-2-methyl propenoate)] were obtained with the fineness at 1.03 dtex and the tenacity at 6.18cN dtex −1.

Degradation of acrylonitrile–ammonium itaconate copolymers

AbstractAcrylonitrile–ammonium itaconate copolymers were prepared by H2O/dimethyl formamide suspension polymerization technique. Differential scanning calorimetry results of the degradation of acrylonitrile–ammonium itaconate copolymers in air are presented. The apparent activation energy of degradation of the copolymer was calculated using the Kissinger method. Effects of copolymerization conditions on the apparent activation energy of copolymer were studied. Increasing the dimethyl formamide concentration in the solvent mixture leads to a rapid increase in the degradation apparent activation energy of acrylonitrile–ammonium itaconate copolymer. The value of the degradation apparent activation energy of the copolymer synthesized in dimethyl formamide solvent increases up to 168.3 kJ mol−1. The apparent activation energy decreases quickly along with an increase in ammonium itaconate concentration, and this change becomes less prominent as the weight ratio of ammonium itaconate/acrylonitrile goes beyond 6/94, ΔEa = 89.4 ± 2.0 kJ mol−1. The apparent activation energy shows a trend of increase with increasing copolymerization temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1708–1711, 2005

Thermal and rheological behaviour of some random aromatic polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological behaviour of seven random Cl-ended aromatic PES/PEES copolymers ( M n ≈ 9500 g mol −1), at various PES/PEES repeating unit ratios, was studied. The glass transition temperatures ( T g), determined by DSC experiments, showed a dependence on copolymer composition significantly different from the ideal linear behaviour expected on the basis of Fox equation. Degradations were carried out in the scanning mode, under flowing nitrogen, in the temperature range 35–650 °C and a single degradation stage was observed for all copolymers. The initial decomposition temperatures ( T i) and the half decomposition temperatures ( T 1/2) were directly determined by TG curves, while the apparent activation energies of degradation ( E a) were obtained by the Kissinger method. In addition, the complex viscosity ( η ∗) of molten copolymers was determined in experimental conditions of linear viscoelasticity. T i, T 1/2, E a, and η ∗ values were depending on copolymer composition, showing a trend similar to that of T g values. The results obtained were discussed and interpreted.

Kinetic study of the degradation of acrylonitrile–acrylamide copolymers

AbstractDifferential scanning calorimetry was used to investigate the degradation of acrylonitrile–acrylamide copolymers in air. The apparent activation energy of degradation of the copolymers was calculated with the Kissinger method. The effects of the copolymerization conditions on the apparent activation energy of the copolymers were studied. Increasing the dimethylformamide concentration in the solvent mixture led to a rapid increase in the apparent activation energy of degradation of the acrylonitrile–acrylamide copolymers. The apparent activation energy decreased quickly as the comonomer acrylamide concentration increased, and this change became less prominent as the acrylamide/acrylonitrile weight ratio increased beyond 5/95. The apparent activation energy increased as the copolymerization temperature increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1017–1020, 2005

Apparent activation energy of degradation of poly[acrylonitrile‐co‐(N‐vinylpyrrolidone)

AbstractDifferential scanning calorimetry results of the degradation of poly[acrylonitrile‐co‐(N‐vinylpyrrolidone)] in air are presented. The apparent activation energy of degradation was calculated using Kissinger's method. The effect of copolymerization conditions on the apparent activation energy was studied. Increasing the dimethylformamide concentration in the solvent mixture led to a rapid increase in the degradation apparent activation energy. The apparent activation energy decreased rapidly with increase in the comononer N‐vinylpyrrolidone concentration, and this change becomes less prominent as the weight ratio of N‐vinylpyrrolidone/acrylonitrile rises above 5/95. The apparent activation energy also increases with increasing copolymerization temperature. Copyright © 2004 Society of Chemical Industry

Molecular dynamics in nanostructured polyimide–silica hybrid materials and their thermal stability

AbstractMolecular motion and thermal stability in two series of nanophase‐separated polyimide–silica (PI–SiO2) hybrid materials with chemically bound components were studied. The hybrids were synthesized from p‐aminophenyltrimethoxysilane‐terminated poly(amic acid)s as PI precursors and tetramethoxysilane as a silica precursor via a sol–gel process. The hybrids differed in their PI chemical structure and chain length (number‐average molecular weight = 5.000, 7.500, or 10.000) and in their SiO2 content, which ranged from 0 to 50 wt %. Differential scanning calorimetry, laser‐interferometric creep rate spectroscopy, and thermally stimulated depolarization current techniques were used for studying the dynamics from 100 to 650 K and from 10−3 to 10−2 Hz. Comparative thermogravimetric measurements were also carried out from 300 to 900 K. Silica nano‐ or submicrodomains that formed affected PI dynamics in two opposite directions. Because of the loosening of the molecular packing of PI chains confined to nanometer‐scale spaces between silica constraints, an enhancement of small‐scale motion, mostly at temperatures below the β‐relaxation region, occurred. However, a partial or total suppression of segmental motion could be observed above the β‐relaxation temperature, drastically so for the shortest PI chains at elevated silica contents and within or close to the glass‐transition range, because of the covalent anchoring of chain ends to silica domains. Large changes in thermal stability, including a 2.5‐fold increase in the apparent activation energy of degradation, were observed in the hybrids studied. A greater than 100 °C rise in long‐term thermal stability could be predicted for some hybrids with respect to pure PI. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1056–1069, 2002

Characterization and degradation of some silicon-containing polyimides

Polysiloxaneimides (PSI) were synthesized by polycondensation of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) with oxydianiline (ODA) and amino-terminated siloxanes of varying molecular weights. The structures of the PSI copolymers were characterized by infra-red (IR), 29Si and 13C nuclear magnetic resonance (NMR) spectroscopies. The dynamics in the interface of PSI copolymers were investigated by proton spin-spin relaxation measurements. The apparent activation energy for degradation of PSI copolymers both in nitrogen and air was studied by thermogravimetry and compared with that of the unmodified polyimide. The activation energies of the degradation process in nitrogen decreased approximately with increasing siloxane content, whereas those in air increased.

Thermogravimetric analysis of a polycyanurate thermosetting material

The thermal degradation of a fully cured polycyanurate thermosetting material was examined by monitoring the mass loss at various temperatures ranging from 200 to 220‡C. The effect of the copper naphthenate catalyst, generally used to facilitate curing, is also studied. A decrease in weight is observed with increasing time at elevated temperatures in the systems containing copper naphthenate, with the onset of degradation occurring sooner with higher concentrations of the copper compound. The apparent activation energy for degradation is 220±30 kJ mol−1.

Effect of catalyst on the thermal degradation of a polycyanurate thermosetting system

The thermal degradation of a polycyanurate thermosetting material was examined by monitoring glass temperature and weight loss at various temperatures ranging from 180 to 220°C. The effect of the cocatalysts, nonylphenol and copper naphthenate, which are generally used to facilitate curing, were also studied. A decrease in Tg is observed with increasing time at elevated temperatures in the systems containing copper naphthenate, with the onset of degradation occurring sooner with higher concentrations of the copper compound. No change in Tg occurred at long times in systems containing only nonylphenol. Weight loss studies were used to calculate an apparent activation energy of degradation. It was found to be approximately 50 kcal/mol. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 127–131, 1997

Poly(dialkoxyethyl itaconates)

The oxidative and non-oxidative degradation of poly(di-methoxy-), poly(di-ethoxy-), poly(di-iso-propoxy-) and poly(di-n-butoxyethyl itaconate) were investigated by thermogravimetry. Characteristic degradation temperatures and apparent activation energies of degradation were determined for the non-oxidative degradation of all the investigated polymers. It was not possible to determine these characteristics in the presence of oxygen as the degradation was accompanied by a secondary exothermic reaction. Based on examination of the monomers, it is supposed that the exothermic reaction is a repolymerisation of the monomers released during the earlier stages of polymer degradation.

Effect of lignin content on thermal degradation of wood pulp

A series of pulps containing between 3.6 and 23% of lignin was prepared by a careful delignification of a high-yield bisulfite pulp. The pulps were subjected to isothermal pyrolysis in a Perkin-Elmer TGS-1 thermobalance. The measurements were carried out at 8 different temperatures from 325 to 360°C under nitrogen atmosphere. The results obtained indicate that the effect of lignin on degradation depends strongly on temperature. Below 330°C, the rate of degradation varied only little with lignin. This variation becomes more important at temperatures above 330°C in that the rate of degradation increases with decreasing lignin content. The apparent activation energy of degradation ranges from 41.4 kcal mol −1 at 23% of lignin to 67.0 kcal mol −1 at 3.7% of lignin.

Thermal degradation of a polyphenylquinoxaline in air and vacuum

AbstractA series of poly[2,2′‐(1,4‐phenylene)‐6,6′‐bis(3‐phenylquinoxalines)] were prepared. These polymers had all the same repeating unit but differed in molecular weight and polymer chain endings. The thermal degradation characteristics in air and vacuum were determined by isothermal weight loss measurements. The temperature coefficients of thermal degradation (apparent activation energies) were also determined. Whereas the apparent activation energies for degradation in air showed a considerable dependency on the type of polymer chain endings, no such effect was observed upon pyrolysis in vacuo. A possible chain‐end unzipping mechanism of degradation in air is postulated to explain these results.