The thermal stability and thermal degradation of blends of syndiotactic polystyrene and polyphenylene ether

Abstract

Blends of syndiotactic polystyrene (sPS) and polyphenylene ether (PPE) have been prepared by co-precipitation from solution, followed by compression moulding. Three different molecular weight polystyrenes were used. Differential scanning calorimetry shows that partial crystallization of the sPS occurs, but a single glass transition indicates that the blend components are miscible in the amorphous phase. Thermogravimetry has been used to compare the thermal stability of the blends and the pure polymers, and IR spectroscopy used to give information on the structural changes consequent upon heating. The three different molecular weight polystyrenes degraded in an identical manner, suggesting that initiation is by random chain scission. The onset of sPS degradation in the blend occurs at higher temperatures than in the pure polymer indicating stabilisaton of that component, whilst degradation of PPE in the blends is accelerated relative to the pure polymer. IR spectroscopy shows that PPE undergoes structural rearrangement in which the ether link is broken and chain continuity is re-established through the methyl group before any mass loss is apparent. The sPS degradation temperatures are coincident with the temperature of this rearrangement and it is proposed that the PPE acts as a radical acceptor, interrupting the intermolecular transfer process in the degrading polystyrene. This cross-termination process limits the PPE rearrangement and consequently reduces the ultimate stability of that polymer.