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Thermal Characteristics of Poly(ethylene oxide)/Polyhedral Oligomeric Silsesquioxanes Nanocomposites

Poly(ethylene oxide) (PEO) is a semi- crystalline, biocompatible, water-soluble polyether, commercially available in wide range of molecular weights (20 000 – 8 000 000). Depending on molecular weight, PEO finds considerable application in many different branches of industry. PEO based electrolytes are among the most extensively studied polymer ionic conductors, but high crystallinity of PEO limits ionic conductivity of these electrolytes at room temperatures. One of the possible ways to reduce the crystallinity of PEO is the incorporation of nanoparticles such as polyhedral oligomeric silsesquioxanes (POSSs) in the PEO matrix. POSSs are nanoparticles composed of inorganic Si8O12 skeleton surrounded by eight organic groups. In this case the general formula is R7R'(SiO1.5)8 where R is isobutyl group and R' is phenyl group or monosupstituted phenyl group. The various POSS nanoparticles were prepared by corner capping reaction of isobutyltrisilanol with the suitable aryltrimethoxysilane. Substituents on phenyl group are methyl, metoxy, fluorine and chlorine. In this work, the series of PEO nanocomposites with different hepta isobutyl polyhedral oligomeric silsesquioxanes were prepared and the influence of POSSs on PEO melting was investigated by means of differential scanning calorimetry (DSC). It was observed that the glass transition temperature, melting temperature and crystallinity of PEO decrease when POSSs with methyl, fluorine or chlorine substituent on phenyl groups are present. Since polymer nanocomposites can be subjected to thermal degradation during processing and application as well, a good knowledge of thermal stability is important. To investigate the thermal behaviour of PEO/POSSs nanocomposites accelerated thermal degradation was performed by means of dynamic thermogravimetric analysis in an inert atmosphere. From the thermogravimetric curves (TG) it is evident that the thermal degradation of PEO matrix occurs through one basic degradation step. To estimate the influence of POSSs nanoparticles on the thermal stability of the PEO matrix, the following characteristics of TG curves were determined: the temperature at 5% mass loss (T5%), the temperature at the maximal degradation rate(Tmax), the maximal degradation rate (Rmax), the conversion at the maximal degradation rate (αmax) and the final mass loss (mf).

nanocomposite, poly(ethylene oxide), POSS

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