Glass transition temperature of styrene-based ionomer controlled over a very wide temperature range by nonpolar plasticizer content and ion content

The plasticization effect by the addition of nonpolar bis(2-ethylhexyl) phthalate (dioctyl phthalate) (DOP) on the glass transition temperatures (T(g)s) of poly(styrene-Na methacrylate) (PSMANa) ionomers was investigated. The matrix T-g (T-g,T-m) and cluster T-g (T-g,T-c) of the ionomers dropped linearly as the DOP content in the PSMANa ionomers enhanced, only when the phase separation of DOP did not occur. Since the T-g,T-m and T-g,T-c of the ionomer increased somewhat linearly with increasing ion content of the ionomer, simple equations were obtained to express the T(g)s of the ionomers using the ion contents (x mol%) and the DOP contents (y wt%) of the ionomers; T-g,T-m (degrees C) = 121 + 3.0x + 2.8y and T-g,T-c (degrees C) = 171 + 6.3x + 2.6y. According to the x-ray scattering results, for the ionomer containing 6.4 mol% of ions, the distance between scattering centers increased from 21 to 22 angstrom when ca. 40 wt% of DOP was added. This suggested that the DOP promoted the mobility of the styrene chains, enhancing the formation of multiplets. On the other hand, for the ionomer containing 22.4 mol% of ions, when ca. 40 wt% was added, the distance between multiplets widened from 18 to 21 angstrom.