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The resistance to the thermal degradation of some polystyrene (PS)-based nanocomposites, loaded with 5% w/w of one of nine novel polyhedral oligomeric silsesquioxanes (POSSs) of general formulaR7R’(SiO1.5)8, whereR= isobutyl, cyclopentyl, or phenyl andR’ = -(CH2)5-CH3, -(CH2)7-CH3, or -(CH2)9-CH3, was studied in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Nanocomposites were prepared by in situ polymerization of styrene in the presence of the appropriate POSS and were characterized by differential scanning calorimetry, to determine the glass transition temperature (Tg), and by nuclear magnetic resonance spectroscopy, to determine the actual filler content which, in all cases, was slightly higher than in the starting mixtures. Nanocomposites were degraded in a thermobalance, in both selected atmospheres, in the 25–700°C temperature range with the formation of small quantities of solid residue at 700°C. The temperatures of 5% mass loss (T5%) were determined to evaluate the resistance to the thermal degradation; the results were higher than for PS. The data obtained were then compared with each other in order to verify if and how much the nature ofRandR’ can influence the thermal stability of the corresponding nanocomposites. [ABSTRACT FROM AUTHOR]

A comprehensive kinetics degradation study is carried out on novel multiple cages polyhedral oligomeric silsesquioxane (POSS)/polystyrene (PS) composites at 5% (w/w) of POSS to assess their thermal behavior with respect to the control PS and other similar POSS/PS systems studied in the past. The composites are synthesized by in situ polymerization of styrene in the presence of POSSs and characterized by 1H-NMR. The characteristics of thermal parameters are determined using kinetics literature methods, such as those developed by Kissinger and Flynn, Wall, and Ozawa (FWO), and discussed and compared with each other and with those obtained in the past for similar POSS/PS composites. A good improvement in the thermal stability with respect to neat polymer is found, but not with respect to those obtained in the past for polystyrene reinforced with single- or double-POSS cages. This behavior is attributed to the greater steric hindrance of the three-cages POSS compared with those of single- or double-cage POSS molecules. [ABSTRACT FROM AUTHOR]

Novel polystyrene (PS)/polyhedral oligomeric silsequioxanes (POSSs) nanocomposites were designed and prepared by in situ polymerization, using, for the first time, three-cage POSS molecules. The synthesized compounds were first characterized by Fourier transform infrared spectroscopy (FTIR) and 1H NMR spectroscopy to verify the obtaining of the designed products before their thermal performance was evaluated and compared with those of pristine PS and the corresponding single-cage POSSs nanocomposites. The thermal behaviour was checked by the means of the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) was also used to confirm the hypothesis about the dispersion/aggregation of the POSS molecules into the polymer matrix. The parameters chosen to evaluate the thermal stability of the investigated compounds, namely temperature at 5% of mass loss (T5%) and solid residue at 700 °C, showed a significant increase in the stability of the polymers reinforced with the three-cages POSS, in comparison to both PS and single-cage POSS reinforced PSs, which therefore turn out to be promising molecular fillers for nanocomposite production. [ABSTRACT FROM AUTHOR]

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]

Abstract: The thermal degradation of three Polyhedral Oligomeric Silsesquioxane/Polystyrene (POSS/PS) nanocomposites of formula R7 R′1 (SiO1.5)8/PS (where R = Cyclopentyl and R′ = Phenyl), at various (3%, 5% and 10%) POSS concentration, was studied in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Compounds were prepared by the polymerization of styrene in the presence of POSS. Degradation was carried out in a thermobalance, in the scanning mode, at various heating rates, and the obtained thermogravimetric (TG) curves are discussed and interpreted. The temperature at 5% mass loss (T 5%) and the activation energy (E a) of degradation of various nanocomposites were determined and compared with each other and with those of unfilled polystyrene (PS). The T 5% and degradation E a values of nanocomposites were higher than those of neat PS, thus indicating a better heat resistance and lower degradation rate, and then a better overall thermal stability. On the basis of the obtained thermal parameters the nanocomposite at 5% of molecular filler appears the most thermally stable. The results are also compared with literature data on similar PS based nanocomposites. [Copyright &y& Elsevier]

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]