L. Abate

Evaluation of the influence of various (ether, ketone and sulfone) groups on the apparent activation energy values of polymer degradation

Abstract The kinetics of degradation of four model polymers containing ether, carbonyl and sulfone groups was studied in both N 2 flow and static air atmosphere, with the aim of evaluating the influence of various groups on the apparent activation energy values ( E a ) of degradation. The initial temperatures of decomposition ( T i ) and the temperatures of half decomposition ( T 1/2 ), were also determined. The degradation of all polymers was carried out in the scanning mode and the Kissinger equation used to evaluate the E a values of the first degradation stage. The results allowed us to make a kinetic stability classification among various groups (sulfone>ketone>ether) which could be explained on the basis of the double-bond character of the polymer chain links. The E a values showed a trend analogous to the glass transition temperatures ( T g ), in agreement with literature reports. By contrast, the characteristic temperatures of decomposition showed a different trend which could not be interpreted on the basis of the experiments until now performed.

A Kinetic Study of the Thermal and Oxidative Degradations of a New Poly(arylene)ether Copolymer

The degradation of a new thermoplastic poly(arylene)ether copolymer was carried out in both dynamic and isothermal heating conditions, under nitrogen flow and in a static air atmosphere. The measurements showed that the copolymer degraded through two stages in both investigated environments with the formation of a stable residue in N2 and complete mass loss in air. The apparent activation energy values associated with the degradation processes were evaluated. The obtained results suggested different degradation mechanisms between N2and air. Results were discussed and compared with those obtained for several polymers previously investigated.

Determination of degradation apparent activation energy values of polymers

The isothermal degradation of three aromatic polyetherketones was studied in an inert environment at various temperatures in the range 683-803 K. In the first degradation stage (mass loss D£20%) a linear increase of D as a function of heating time (t) was observed and the corresponding kinetic D=Do+bt equations at various temperatures were directly drawn by smoothing the experimental TG data. The b values, which represent the mass loss rates during degradation, increased as a function of temperature according to Arrhenius-type equations, from which degradation Ea values were determined, which appear in agreement with those from literature methods. Some differences observed were discussed and interpreted.

Kinetic study of the thermal degradation of some poly(arylenether)s containing naphthalene units

Abstract The degradations of five aromatic thermoplastics, containing carbonyl, ether and sulfone linkages and in whose repeating units the –ArCONaphCOAr– moiety (where Ar=1,4 substituted phenylene; Naph=2,6 substituted naphthalene) was present, were performed under N 2 flow in dynamic heating conditions. The obtained results suggested that degradations occurred through random chain scission followed by branching and crosslinking, which partially superimposed with the initial process. The Kissinger method was used to determine the apparent activation energy ( E a ) associated with the first degradation stage, and double linear relationships, attributable to slow diffusion of degradation products in the melt, were found in some cases. A thermal stability classification among the studied polymers was made on the basis of the obtained E a values. This classification was compared with those previously obtained for two analogous groups of thermoplastics and some correlations between thermal stability and polymer chain structure were drawn.

Kinetic study of the thermal and oxidative degradations of poly(arylenether)s containing quinoline units

Abstract The degradations of five aromatic thermoplastics, in whose repeating units various structures are linked to the same -ArCOQCOAr- moiety (where Ar=1,4-substituted phenylene and Q=3,7-substituted quinoline), were performed in dynamic heating conditions in the temperature range 35–950°C, under nitrogen flow and in static air atmosphere. Experiments under nitrogen suggested that degradations started by random chain scissions, to which branching and crosslinking superimposed at higher temperature, with the formation of residues stable up to 950°C; those in oxidative environment indicated that degradations were due to several processes which were simultaneous at low heating rate and that oxidative stages were involved, as supported by the complete weight loss before the overall temperature scanning. The apparent activation energy values associated with the first degradation stage were obtained by the Kissinger method. Results in inert atmosphere suggested that different linkages were involved in the initial chain scission processes of various polymers and that the comprehensive degradation mechanisms were different from those in air. Anomalous double Kissinger straight lines were found for one of the polymers investigated. The results were discussed and compared with those previously obtained for a similar group of aromatic polymers.

Dumbbell-shaped polyhedral oligomeric silsesquioxanes/polystyrene nanocomposites: The influence of the bridge rigidity on the resistance to thermal degradation

A comparative study concerning the resistance to the thermal degradation of polystyrene-based nanocomposites loaded with five novel aromatic dumbbell-shaped polyhedral oligomeric silsesquioxanes was carried out in dynamic heating conditions. The fillers were formed by two identical silicon cages R7(SiO1.5)8 (R = isobutyl) linked to several aromatic bridges (Ar, Ar–Ar, Ar–O–Ar, Ar–S–Ar and Ar–SO2–Ar) where Ar = p-C6H4. Nanocomposites were prepared by in situ polymerization of styrene in the presence of 5% of appropriate polyhedral oligomeric silsesquioxanes. The actual filler content in the products obtained, which was checked by 1H NMR spectroscopy, resulted in all cases slightly higher than that in starting mixtures. Glass transition temperature (Tg) was determined by differential scanning calorimetry. Thermogravimetric (TG) and differential thermogravimetric (DTG) analysis were carried out in both flowing nitrogen and static air atmosphere, and temperatures at 5% mass loss (T5%) were determined to investigate the resistance to the thermal degradation. The results obtained were compared with each other and discussed. The resistance to the thermal degradation showed modest increments in respect to neat polystyrene, differently from analogous nanocomposites containing as fillers aliphatic bridged polyhedral oligomeric silsesquioxanes, as supported by scanning electron microscopy measurements which evidenced polyhedral oligomeric silsesquioxanes auto-aggregation phenomena. This behaviour was interpreted as due to the rigidity of polyhedral oligomeric silsesquioxanes aromatic bridges, which leads to low miscibility between filler and polymeric matrix.

Binding of glyphosate by open‐chain polyammonium cations

Interaction of glyphosate (N-(phosphonomethyl)-glycine) with six polyamines (ethylendiamine, cadaverine, putrescine, triethylenetetramine, spermine, and tetraethylenepentamine) was studied potentiometrically. Several species of different stoichiometry are formed in the various systems, according to the general formation reaction [Formula: see text] (where A = amine and glp = glyphosate). The complex species formed are always [Formula: see text] with r = 1 … (n + 2) (n = maximum degree of protonation of amines). The stability of various complexes is a linear function of charges involved in the formation reaction, and can be expressed as logKij = 0.9(±0.2)ζ (where ζ = i [3 - j]). From the temperature dependence of formation constants, ΔH° (and TΔS°) values have been obtained. Formation percentages of mixed glyphosate-polyammonium cation complexes are relevant also in low concentration conditions, and this means that these species may play a significant role in the speciation of natural fluids containing the reactants.

Thermal behaviour of uranium(VI) complexes. Uranyl acetate dihydrate-thiourea system: Synthesis and decomposition

The solid-state syntheses of uranyl acetate adducts with thiourea were attempted directly in a DSC apparatus according to the scheme: UO2Ac2·2 H2O(s)+n thiourea(s) → → UO2Ac2·thiourean(s)+2 H2O(v) (n=1–6), and the correspondingδH values were evaluated. At all stoichiometric ratios the same UO2Ac2·thÌourea product was obtained, to which a pentagonal bipyramidal structure was attributed. Thermoanalytical (TG and DTG) and infrared spectra measurements were also performed and agree with the DSC results.ZusammenfassungIn einer DSC-Apparatur wurde die Synthese von Uranylacetat-Thioharnstoff-Addukten in situ durch Festkörperreaktion entsprechend dem Schema UO2AC2 (n=1−6) ausgeführt. Die entsprechenden δH-Werte wurden berechnet. Für alle stöchiometrischen VerhÄltnisse wurde das gleiche UO2Ac2 · Thioharnstoff-Produkt erhalten, dem eine pentagonale bipyramidale Struktur zuzuordnen ist. Die Ergebnisse thermoanalytischer (TG und DTG) und infrarotspektrophotometrischer Messungen stimmen mit den DSC-Ergebnissen überein.РЕжУМЕНЕпОсРЕДстВЕННО В пР ИБОРЕ Дск Был пРОВЕДЕ Н тВЕРДОтЕльНыИ сИНтЕ ж АДДУктОВ АцЕтАтА УРАНИлА с тИО МОЧЕВИНОИ пО слЕДУУЩ ЕИ схЕМЕ РЕАкцИИ: UO2Ac2 · 2 H2O (тВ) +n тИОМОЧЕВИНА (тВ.) → → UO2Ac2 · тИОМОЧЕВИНА (тВ.) +2H2O(пАРы), rДЕп=1−6. ОпРЕДЕлЕНы жНАЧЕНИьδН. НЕсМОтРь НА РАжлИ ЧНыЕ стЕхИОМЕтРИЧЕскИЕ с ООтНОшЕНИь Вжьтых ИсхОДНых ВЕЩЕстВ, Был пОлУЧЕН ОДИН И тОт жЕ п РОДУкт UO2Ac2 · тИОМОЧЕВИНА, кОтО РОМУ БылА пРИпИсАНА стРУк тУРА пьтИУгОльНОИ БИ пИРАМИДы.

Heat capacities of sixteen small peptides (N-acetyl-N'-methylamino acid amides) measured by differential scanning calorimetry

Abstract The molar heat capacities at constant pressure of N -acetyl- N′ -methylamides of glycine, l -and dl -alanine, dl -2-aminobutyric acid, l - and dl -proline, l - and dl -valine, dl -norvaline, l - and dl -leucine, dl -norleucine, l - and dl -isoleucine and l - and dl -phenylalanine have been measured by differential scanning calorimetry from 318 K to about 20 K below their melting points. Values at 298.15 K have been obtained by extrapolating the smoothed fitting equations. The C * p ,m values at 298.15 K of both l - and dl -amino acid derivatives, including that of glycine, increase very linearly as a function of their molar masses. Slopes, giving 25±1 J K −1 mol −1 per methylene group, are coincident with those of the corresponding amino acids. Isomeric compounds (iso- and noramino acid derivatives) show a small departure from linearity, whereas proline and phenylalanine derivatives present somewhat larger and decidedly strong deviations, respectively.

Complex formation between imidazole and carboxylate ligands in aqueous solution

We report the results of a potentiometric study on the formation of weak complexes between imidazole (im) and acetate, malonate, and citrate (L), at T=25°C. Formation of protonated species Hj (im)(L), in which j=1 for acetate, j=1, 2 for malonate and j=1, 2, 3 for citrate, was found. The formation of weak complexes between N-ligands and O-ligands may be used to interpret the behavior of these classes of compounds in natural fluid and/or in biological systems, as regards inter-or intra-molecular interactions.