Chain Conformation, Packing, and Folding Structures of Poly(L-Lactic Acid) in Glassy State as Studied by ¹³C Solid-State NMR and Selective Isotope Labeling

Deep quenching of semi-crystalline polymer from the melt state down to below glass transition temperature results in the glassy state. Comparing with the melt grown process, the cold-crystallization of glass samples usually exhibit a much higher overall crystallization rate, which triggers numerous investigation of the glassy state. The short-range-ordered nature of polymer in the glassy state poses difficulty in analyzing the chain conformation, packing and folding structure by conventional characterization techniques. Here, we synthesized ¹³C single and double sites labeled PLLA and investigated the structures of the glassy sample in detail. It was demonstrated that the conformational/packing/folding structures are quite similar between glassy and crystalline states. This result suggests that even rapidly quenched glassy sample possess the same local structure as the crystalline form.