Elucidations of Chain-Level Structure of Semicrystalline Polymer Freeze-Dried from a Dilute Solution by Solid-State NMR spectroscopy

Chain entanglements play a crucial role in polymer crystallization, yet their effects on crystallization remain not fully understood. Freeze-drying is one way to potentially preserve disentangled states of long polymer chains. In fact, it is known that freeze-drying (FD) significantly accelerates the crystallization kinetics of semicrystalline polymers. However, the chain-level structure of the FD polymer chains without a long-range order (glass) has been a debatable matter. In this study, we investigate the effect of freeze-drying on single chain-level structures of ¹³CH₃ enriched poly(L-lactic Acid) and ¹³CH enriched poly(D-lactic acid) racemate by using ¹H-¹H spin diffusion via ¹³C detection solid-state NMR spectroscopy. Spatial distributions of PLLA and PDLA glassy chains in the range of a few Å – 30 nm are evaluated via ¹H-¹H spin diffusion. This analysis provides core-shell morphology of single chains where the outer shell layers include both PDLA and PLLA mixture and the inner core possess a single component.