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Four random, differently ended (-CI, [-NH.sub.2], -OH, and -[COO.sup.-]), polyethersulfone/polyetherethersulfone (PES/PEES) copolymers were studied to investigate the influence of chain ends on thermal and rheological behaviors. The number average molar mass ([M.sub.n] ≅ 9500 [g.mol.sup.-1]) and the PES/PEES ratio (40/60) of all copolymers investigated were checked by [sup.1.H] NMR spectra. Thermal degradations were carried out in the scanning mode and initial decomposition temperatures ([T.sub.i]) and activation energy values of degradation ([E.sub.a]) were obtained. Glass transition temperature ([T.sub.g]) was determined by differential scanning calorimetry and complex viscosity (η*) rheological measurements in isothermal heating conditions (T = 270°C). All parameters determined were largely affected by copolymer chain ends and decreased according to the same order, -OH >[-NH.sub.2] > -CI gt; [-COO.sup.-]. The results were discussed and interpreted. POLYM. ENG. SCI., 49:1477-1483, 2009. (C) 2009 Society of Plastics Engineers, INTRODUCTION In recent years our group has been interested in the investigation of aromatic thermoplastic polymers containing ether, ketone, and sulfone groups (1-9). These polymers show usually good thermal and [...]

Five novel bridged heptaphenyl polyhedral oligomeric silsesquioxanes (POSSs), in which two identical silicon cages R7(SiO1.5)8 (with R = Phenyl) are linked to various aliphatic [(CH2)n with n = 2, 6 and 10] and aromatic (Ar–Ar and Ar–O–Ar, where Ar = p-C6H4) bridges, were synthesized. The obtained compounds were characterized by elemental analysis and 1H NMR spectroscopy, and the results were in very good agreement with those of expected products. The synthesized heptaphenyl POSSs were thermally degraded, in dynamic heating conditions (25–700 °C), in both flowing nitrogen and static air atmosphere. The temperatures at 5% mass loss (T5%) and residues at 700 °C were thus determined to evaluate their resistance to thermal degradation, but no substantial difference was found between the values in the two studied environments. The obtained T5% values were much higher than those of the corresponding isobutyl and cyclopentyl POSSs we investigated in the past. Also, the T5% values of the phenyl POSSs with aliphatic bridges decreased quite linearly on increasing the number of bridge carbon atoms (nC). This behaviour was interpreted and attributed to the presence of the external corona formed by voluminous phenyl groups. The residue at 700 °C, which was largely higher than those of the corresponding isobutyl and cyclopentyl POSSs, was a further confirmation of the better thermal stability of the compounds here studied. [ABSTRACT FROM AUTHOR]

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 silsesquioxane's aromatic bridges, which leads to low miscibility between filler and polymeric matrix. [ABSTRACT FROM AUTHOR]

Abstract: The kinetics of the isothermal degradation in static air atmosphere of four well known polymers, polyethylene (PE), polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA) was studied by both a long-term (more than three years) experiment at relatively low temperature (423 K) and a set of short-term experiments at higher temperatures. The activation energy (E a) values of degradation were determined by both the MacCallum and Wilkinson literature methods, and were compared with those obtained through a new very simple method we set up, based on the direct regression of TG mass loss data. About two years ago we published the results concerning PE and PS because their mass losses during long-term experiments were sufficiently high. The long-term degradation experiments were continued until now and in this second part we report the results concerning PC and PMMA. The degradation E a values calculated from short-term experimental data through the three different methods were in good agreement with each other for both PC and PMMA, thus confirming the general applicability of our simple method for the determination of E a. The experimental data at lower temperature of PC were not in agreement with those at higher temperatures, thus confirming the low reliability of the kinetic parameters (and then of lifetime predictions) at low temperature determined by experiments at higher temperatures. Partially disagreeing results were obtained for PMMA, which were discussed and interpreted. [Copyright &y& Elsevier]

Abstract: The thermooxidative degradation of four well known polymers, polyethylene (PE), polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA), was carried out in a thermogravimetric (TG) analyser, at various temperatures (in the 473–533 K range), in isothermal heating conditions. The resulting set of experimental TG data was used to determine the apparent activation energy (E a) of degradation through two isothermal literature methods, as well as through a very simple method we set up, based on the direct regression of the experimental mass loss data, in order to verify the general applicability of our method to various polymers. The results from different methods were in good agreement. Degradation experiments in dynamic heating conditions, which were also performed, gave E a values in good agreement with those in isothermal heating conditions for PS, PC and PMMA, while for PE a large discrepancy was observed, which was discussed and interpreted. The results suggested the general applicability of our method to all polymers, independently on their structure and degradation mechanism. A long-term (about 13 months) isothermal degradation experiment was also carried out with the same polymers at relatively low temperature (423 K). Only PE and PS evidenced appreciable mass loss in the investigated period, but the experimental data were not in agreement with those from the short-term degradations at higher temperatures, thus suggesting different degradation kinetics, and a low reliability of the lifetime predictions for polymers in service based on experiments at higher temperatures. [Copyright &y& Elsevier]

Two series of novel dumbbell-shaped polyhedral oligomeric silsesquioxanes (POSSs), fully functionalized with phenyl groups at the corner of the silicon cages, were used to prepare polystyrene (PS) nanocomposites through the method of in situ polymerization. The percentage of the molecular filler reinforcement was set as 5% w/w of POSS and was checked by 1H-NMR spectroscopy. The obtained nanocomposites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Thermal and morphological properties were evaluated and compared among the nanocomposites obtained using the two different series of dumbbell-shaped POSSs and with the net PS. The thermal parameters for the prepared nanocomposites were very high when compared with those of neat PS, and they evidenced significant differences when an aliphatic or aromatic bridge was used to link the silicon cages. SEM analysis results allow us to hypothesize a justification for the different resistance to thermal degradation showed by the two series of molecular reinforcement. [ABSTRACT FROM AUTHOR]