Nucleation\nSite Memory in the Spherulite Films of\nPolydisperse Poly(l‑lactic acid)

Molecular weight distribution (MWD)\nis a unique feature\nof polymers,\nwhich endows various properties of polymer materials with broadly\nregulatable scopes. The various chain dynamics and crystallization\nbehaviors of different molecular-weight polymers coexisting within\nthe same polydisperse system would lead to unique crystallization\nphenomena and aggregating structures. Recently, an MWD-induced polymorphism\ntexture of poly(l-lactic acid) (PLLA) is reported, called\n nested PLLA spherulites, where one crystal form is embedded inside\nthe other. Here, an interesting nucleation site memory phenomenon\nis reported for the PLLA thin films, where the nucleation sites of\nspherulites recover around the initial positions, even after multiple\nmelting–crystallizing cycles. The nucleation site memory strongly\nassociates with solution processing and the nested spherulites. After\n the impact of heterogeneous nucleation is excluded, it is demonstrated\nthat the nucleation site memory originates from MWD. The insights\nprovided in this work deepen the fundamental understanding of the\ninfluence of MWD on the structure evolution during polymer processing.