Unraveling the Physicochemical Properties of Poly(2-n-propyl-2-oxazoline), a Promising Pharmaceutical Excipient

Poly(2-alkyl/aryl-2-oxazoline)s (PAOx) are biocompatible polymers that are increasingly being applied in the biomedical field. Understanding their properties is crucial to rationally applying them in the said field. Despite this increasing interest, many fundamental properties of PAOx, such as the semicrystalline nature of poly(2-n-propyl-2-oxazoline) (PnPrOx) have not been fully elucidated yet, especially for higher molar mass polymers. In the present work, the crystallinity of PnPrOx was studied by using modulated DSC as well as small-angle and wide-angle X-ray scattering. This study reveals that high molar mass PnPrOx show a much richer phase behavior than their amorphous low molar mass counterparts. For instance, aqueous solutions turn cloudy upon prolonged exposure to high temperature due to crystallization of the phase-separated high polymer concentration mesoglobules. Moreover, dry solid samples display polymorphisms as well as multiple melting behavior due to the presence of different crystal sizes and overlapping crystallization and melting events. This work suggests that additional research into the semicrystalline properties of other higher molar mass PAOx might be required to evaluate whether they have similar behavior to higher molar mass PnPrOx. Additionally, the results presented in this paper will allow for the rational development and design of pharmaceutical formulations containing PAOx, as it elucidates some of their fundamental properties.