Strong Hydrogen Bonds Sustain Even-Odd Effects in Poly(ester amide)s with Long Alkyl Chain Length in the Backbone.

Abstract

The number of methylene groups between strongly interacting functional groups within polymer repeating units induces even-odd effects on thermal and mechanical properties. However, detailed studies correlating the even-odd effect with structural changes are still lacking. In this work, we establish correlations between the structure and thermal properties of poly(ester amide)s containing long alkyl chain lengths. The even-odd effect impacts the thermal properties, including the melting temperature and crystallinity degree. It influences the spherulitic morphology of poly(ester amide)s, controlling the appearance of banding. We demonstrate that even-odd effects in poly(ester amides)s persist even with 27 CH₂ groups within the repeating unit, an effect due to strong hydrogen bonds caused by the amide groups. Our X-ray studies reveal that the even-odd effect originates from changes in the crystalline structure of the materials. This work helps elucidate the role of strong intermolecular interactions (i.e., hydrogen bonding) on the even-odd effect in long-chain poly(ester amides).