Discovering crystal forms of the bio-based nylon 5O monomer 1,5-pentanediamine-O-phthalate: insight into the crystal structures, transformations and stability

Abstract

Nylon 5O is one of the new bio-based nylon materials since its raw material 1,5-pentanediamine is prepared by biological methods using biomass as a raw material. Original high-quality monomers are the basic requirement for the preparation of high-performance polymer materials. 1,5-pentanediamine-O-phthalate (PDA-OPA), the monomer of nylon 5O that can be directly used for polymerization, can be prepared effectively and simply by a crystallization method. In this report, we found and obtained seven crystal forms of the PDA-OPA salt, three hydrates, one methanol solvate, and three anhydrous forms. Their crystal structures were determined and characterized physicochemically by SCXRD, PXRD, and FTIR methods. Moreover, the thermal behaviors were characterized by DSC, TGA, HSM and VT-PXRD. To unravel the rationale for the stabilization of their crystalline assembly and the contribution of individual intermolecular interactions to the stability of each form, computational studies have been explored in-depth through Hirshfeld surface analysis, energy frameworks, and lattice energy comparison. IRI analysis further provided a visual demonstration of the intermolecular interactions. The structure–property relationship between PDA-OPA pseudopolymorphs was finally analyzed and established. Particularly, the production process of the trihydrate is green and sustainable when compared to those of the other crystal forms. Thus, this study not only develops a strategy to control the preparation of target crystal forms but also can be greatly helpful to the green production and industrialization of bio-based nylon 5O.