Chain Trajectory of Semicrystalline Polymers As Revealed by Solid-State NMR Spectroscopy

Over the last half century, chain-folding structure of semicrystalline polymers is debatable of matter in polymer science. Recently, 13C-13C double quantum (DQ) NMR spectroscopy combined with 13C selective isotope labeling has been devel-oped to investigate re-entrance sites of the folded chains, mean values of adjacent re-entry number \textless n\textgreater and fraction \textless F\textgreater of semi-crystalline polymers. This viewpoint highlights the versatile approaches using NMR and 13C isotope labeling for revealing i) chain trajectory in melt- and solution-grown crystals, ii) conformation of the folded chains in single crystals, iii) self-folding in the early stage of crystallization, and iv) unfolding of folded chains under stretching.