A Crystal and Particle Engineering Approach To Modulating the Properties of Polymer

Polymer-based cocrystals represent a highly promising subclass of multicomponent solids. One interesting aspect of these materials is related to the possibility of obtaining isostructural crystals simply by changing the chain length of the polymer used. In this study, we perform an in-depth investigation of the solid-state features of several isostructural ternary polymer-based cocrystals composed of caffeine, 5-fluoroanthranilic acid, and polyethylene glycols of varying chain lengths. Thermal analyses, synchrotron powder X-ray diffraction studies, and atomic-resolution transmission electron experiments were used to investigate the solid-state features of the multicomponent solids. We observed that cocrystallization of polyethylene glycol with caffeine and 5-fluoroanthranilic acid led to a solid with a melting point at least 50 °C higher than that of the pure polymer. We also discovered that further tuning of the melting behavior can be achieved through particle engineering, whereby the crystallite size and strain are controlled by the length of the polymer chain. A better understanding of the solid-state features of such materials would allow, in the near future, the development of polymer-based cocrystals with tailored solid-state properties.