Plasticization, Antiplasticization, and Fragility in Blends of Polyvinyl Butyral and Polyethylene Glycol Dimethyl Ether

Blends of polyvinyl butyral (PVB) and polyethylene glycol dimethyl ether (PEGDME) with low molecular weight (M over bar w${\bar M_{\mathrm{w}}}$= 250 g mol(-1)) show two calorimetric (for PEGDME content higher than 11% by weight) and mechanical glass transitions. Their substantial changes in the relative content of the two components are explained by considering the self-concentrations of both polymers determined by the connectivity of their own chains. Increasing content of PEGDME lower the glass transition temperature T-g of PVB (the component with the highest T-g) by about 100 K, also causing a progressive and significant increase of its fragility (following the Angell's strong/fragile liquids classification scheme). Strengthening of polymer blends is observed in the fully glassy region, quite below the T-g's of both the components, with the storage modulus E & PRIME; becoming more than a factor 2 higher than that of neat PVB. The progressive increase of E & PRIME;, without any change of slope, points to structural homogeneity of blends determined by compatibility of components, as a result of interchain interactions activated by the polar groups of both polymers. The present results reveal that PEGDME plasticizes PVB when the blend is in the fully rubbery state while acting as an anti-plasticizer in the fully glassy state.