Short-Range Order of Mesomorphic Phase of a Semi-crystalline Polymer by Solid-State NMR: Isotactic Polypropylene

Mesophase is intermediate phase between crystalline and melt state. Characterization of short-range structures of disordered mesomorphic phase without long-range order is challenging issue in polymer characterization. The short range order was considered same as $\alpha^{\mathrm{\thinspace }}$or $\beta \quad i$PP, or neither. In this work, a new strategy using $^{\mathrm{13}}$C-$^{\mathrm{13}}$C through space interactions as well as molecular dynamics based on chemical shift anisotropy (CSA) re-orientation is proposed for evaluating short-range order of mesophase of isotactic-polypropylene ($i$PP). $^{\mathrm{13}}$C-$^{\mathrm{13}}$C double quantum (DQ) build up curves of $^{\mathrm{13}}$C 15 percent CH$_{\mathrm{3}}$ selectively labeled iPP and spin dynamics simulations elucidate that local packing structures in mesophase is very close to that in $\beta $ phase. Moreover, exchange NMR proves that the crystalline chains perform large amplitude motions in all $\alpha $, $\beta $, and mesophase. The correlation time of overall dynamics of stems in mesophase follows the same Arrhenius line with that of $\beta $ phase but is largely deviated from the Arrhenius line of the $\alpha $ phase. Through the obtained results, it is concluded that short-range order in mesophase is exceedingly close or same to those in $\beta $ phase.