Folding of Polymer Chains in Early Stage of Crystallization

Understanding the structural formation of long polymer chains in the early stage of crystallization is one of the long-standing problems in polymer science. Using solid state NMR, we investigated chain trajectory of \textit{isotactic} polypropylene in the mesomorphic nano-domains formed via rapid and deep quenching. Comparison of experimental and simulated $^{\mathrm{13}}$C-$^{\mathrm{13}}$C Double Quantum (DQ) buildup curves demonstrated that instead of random re-entry models and solidification models, individual chains in the mesomorphic form $i$PP adopt adjacent reentry sequences with an average folding number of \textless n\textgreater $=$ 3-4 (assuming an adjacent re-entry fraction of \textless F\textgreater of 100{\%}) during mesomorphic formation process via nucleation and growth in the early stage.