Folding of Polymer Chains in the Early Stage of Crystallization

Understanding the structure formation of an ordered domain in the early stage of crystallization is one of the long-standing issues in polymer science. In this study, we investigate the chain trajectory of isotactic polypropylene ( i PP) formed via rapid and deep quenching, using solid-state NMR spectroscopy. Comparisons of experimental and simulated 13 C– 13 C double quantum (DQ) buildup curves demonstrated that individual i PP chains adopt adjacent re-entry sequences with an average folding number ⟨ n ⟩ = 3–4 in the mesomorphic form, assuming an adjacent re-entry fraction ⟨ F ⟩ of 100%. Therefore, long flexible polymer chains naturally fold in the early stage of crystallization, and folding-initiated nucleation results in formation of mesomorphic nanodomains.