Determination of Local Packing Structure of Mesomorphic Form of Isotactic Polypropylene by Solid-State NMR

Understanding the local packing structures of a disordered mesomorphic phase is a challenging issue in polymer characterization. In this work, 13 C– 13 C through-space interactions, as well as a molecular dynamics analysis based on the reorientation of chemical shift anisotropy (CSA), were proposed for the evaluation of the local packing structure of the mesomorphic form of isotactic polypropylene ( i PP). 13 C– 13 C double quantum (DQ) buildup curves of 13 C 15% CH 3 selectively labeled i PP and spin-dynamics simulations demonstrated that the local packing structures in the mesomorphic form were very similar to the packing in the β phase. Moreover, centerband only detection of exchange (CODEX) NMR proved that the correlation time ⟨τ c ⟩ of the overall stem dynamics in the mesomorphic form followed the same Arrhenius line observed for the β phase, but it deviated from that for the α phase. Based on both structural and dynamic results, it was concluded that the local packing structure in the mesomorphic form was exceedingly close or the same as that of the β phase.