Thermal decomposition studies on polyurethane elastomers reinforced with polyhedral silsesquioxanes by evolved gas analysis

In this work, we report on the thermal stability of nanohybrid polyurethane (PU)/polyhedral oligomeric silsesquioxanes (POSS) elastomers analyzed by evolved gas analysis (EGA). Functionalized POSS were chemically introduced into PU structure as pendant groups (1,2-propanediolizobutyl POSS (PDI-POSS), disilanollsobutyl POSS (DSI-POSS)) or as chemical crosslinks (octa(3-hydroxy-3-methylbutyldimethylsiloxy) POSS (OCTA-POSS)). EGA results of the thermal degradation of the PU/POSS hybrid elastomers have demonstrated that the hybrid systems are slightly more thermally stable when compared to the unmodified PU matrix, as evidenced by reduced amounts of volatile degradation products. It was found that the thermal decomposition of polyurethane materials reinforced with POSS starts from about 300 degrees C via urethane bonds breakage. In lower temperature region the modified polyurethanes decompose to some low molecular weight compounds and intermediates with hydroxyl and amine groups. At temperatures above 350 degrees C evolution of hydrocarbons, aldehydes, alcohols, amines, cyclic species and low molecular weight compounds - carbon monoxide, carbon dioxide, water and ammonia was recorded. Furthermore, the inclusion of POSS in the PU network directly influences the degradation pathways of both the soft and hard block components of the elastomers it has been observed that the POSS/PU hybrid systems show reduced levels of CO2 and changed levels of characteristic ion fragments, e.g. m/z 42 related to hydrocarbons and THF.