Melting Behavior of Poly(Ethylene Oxide)/POSS Nanocomposites

Poly(ethylene oxide) (PEO) is a semi-crystalline, biocompatible, water-soluble polyether commercially available in wide range of molecular weights (20000 – 8000000). Depending on molecular weight, PEO finds considerable application in many different branches of industry [1-3]. Since the discovery of the ionic conductivity of poly (ethylene oxide) complexes with alkali metal salts, polymer electrolytes have been extensively investigated as promising candidates to prepare thinner, lighter and safer lithium ion batteries [4]. However, the typical linear PEO does not meet the production requirements because of its insufficient ionic conductivity due to the high crystallinity of the PEO chains. Solid polymer electrolyte (SPE) based on PEO usually shows low ionic conductivity at room temperature which is not suitable for practical applications. PEO shows significant conductivity above the melting point. There are a lot of different approaches to reduce the crystallinity and hence to improve the ionic conductivity of PEO-based electrolytes, including blending, modifying or making PEO derivatives. One possible way is introducing the nanofillers, such as polyhedral oligomeric silsesquioxanes (POSS) in polymer matrix [5]. 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 mono-substituted phenyl group. The various POSS nanoparticles were prepared by corner capping reaction of isobutyltrisilanol with the suitable aryltrimethoxysilane. Substituents on the phenyl group are methyl, methoxy, 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. It was observed that the glass transition temperature (Tg), melting temperature (Tonset) and crystallinity (%C) of PEO decrease when POSSs with methyl, fluorine or chlorine substituent on phenyl groups are present.