Self-nucleation enhances the stability of the polymorphs present in triple polymorphic polythioethers

This work examines the self-nucleation of three different polymorphic alternating polythioether homopolymers, i.e., DMDS- alt -DVE, DMDS- alt -TEGDVE and DMDS- alt -BBDVE. The repeating unit of these materials consists of an identical sulfur-containing part and ether functionalities that vary in chemical structure. All of the materials show three different polymorphic crystal phases, denoted by their distinct melting temperatures as: very low-temperature melting phase ( V L − T m ), low-temperature melting phase ( L − T m ) and high-temperature melting phase ( H − T m ). A detailed self-nucleation study was performed by differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM). The different self-nucleation Domains were determined for each of the polymers, and the polymorphs that formed in each Domain were assigned. Self-seeding promoted the crystallization of the highest thermodynamically stable phase that was present in a given polythioether (e.g., DMDS- alt -DVE) and substantially increased its quantity reducing the formation of less stable phases. PLOM was indispensable to identify the multiple polymorphs present in the samples. This work establishes a robust testing protocol for polymorph selection in sulfur-containing polymers and offers thermal processing parameters for achieving desired crystal structures in functional polymer materials. • DSC was essential to determine the different self-nucleation Domains. • PLOM was indispensable to identify the polymorph being formed in each self-nucleation Domain. • The triple polymorphic polythioethers displayed no melt memory ( DIIa ), only self-seeding ( DIIb ). • Self-seeding enhanced the formation of the thermodynamically more stable polymorph present in the material.