Control of Guest Thermal Release by Crystalline Host Orientation

Thermal release of guest molecules from poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films, exhibiting host-guest co-crystalline (CC) phases with orientation of their chain axes being preferentially parallel or perpendicular to the film plane (c≈ and c⊥ orientations), is studied. TGA analyses show that, for all the considered CC PPO films, temperatures of guest release for CC films with c≈ orientation are definitely higher than those for CC films with c⊥ orientation, with differences even higher than 100 °C. Correspondingly, DSC scans of CC films with c⊥ orientation show separated endothermic peaks of guest release and melting, while CC films with c≈ orientation only exhibit one broad endothermic peak with superimposed guest release, glass transition (Tg), and melting (Tm) phenomena. This control of temperatures of guest release could be helpful to maximize the thermal stability of host-guest PPO co-crystalline phases and to tailor temperatures of active guest release