Intramolecular and Intermolecular Packing in PolymerCrystallization

Recently, the chain-folding structure of 13C-labeled poly(l-lactic acid) (PLLA) with different molecular weights (M) of 46K (small, s), 90K (middle, m), and 320K g/mol (large, l) in the solution-grown crystals [Macromolecules 2018, 51, 8729–8737] was studied by solid-state nuclear magnetic resonance (ssNMR). In this work, the chain-folding and packing structures, long period, and morphology of 13C-labeled s-, m-, and l-PLLA in the melt-grown crystals crystallized at Tc = 90 and 150 °C are investigated by ssNMR, small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM), respectively. All the s-, m-, and l-PLLA adopt thermodynamically stable α crystals and large spherulites with a diameter of ∼2 mm at Tc = 150 °C. A large supercooling induces kinetically favored disordered α′ crystals and nodular structures for all three samples. By comparing the experimental 13C–13C double quantum (DQ) buildup data with the simulated ones, we found that all three PLLA ...