Bound solvent in different stereoregular syndiotactic polypropylene gels

The coagulation size of the solvent in syndiotactic polypropylene (sPP)/o-dichlorobenzene gels was investigated for different stereoregular samples with racemic diads of 98% (sPP98) and 83% (sPP83) using thermal analysis, optical microscopy, and solid-state high resolution 13C nuclear magnetic resonance (NMR). For the sPP98 gel, the coagulation size of freezable bound solvent was smaller than that in the sPP83 gel. The non-crystalline region of the sPP83 gel is large due to the incomplete stereoregularity, so that a large coagulation of the solvent occurs. The weight contents of the crystalline, amorphous, and interphase components were estimated using solid-state high resolution 13C NMR. The interphase weight content was comparable with that of the non-freezable solvent estimated by thermal analysis, which implies that the non-freezable solvent is bound in the interphase. The coagulation size of the solvent in the sPP98 gel increased with gelation temperature. Large spherulites are formed at higher gelation temperatures; therefore, the non-crystalline region between lamellae is larger, which results in the large coagulation size of the solvent.