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

Abstract

The plasticization effect by the addition of nonpolar bis(2‐ethylhexyl) phthalate (dioctyl phthalate) (DOP) on the glass transition temperatures (Tgs) of poly(styrene‐Na methacrylate) (PSMANa) ionomers was investigated. The matrix Tg (Tg,m) and cluster Tg (Tg,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 Tg,m and Tg,c of the ionomer increased somewhat linearly with increasing ion content of the ionomer, simple equations were obtained to express the Tgs of the ionomers using the ion contents (x mol%) and the DOP contents (y wt%) of the ionomers; Tg,m (°C) = 121 + 3.0x + 2.8y and Tg,c (°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 Å 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 Å.