Cocrystallization Phenomenon between the H and D Species of<i>Isotactic</i>Polypropylene Blends As Revealed by Thermal and Infrared Spectroscopic Analyses for a Series of D/H Blend Samples

Abstract

Cocrystallization phenomenon between the hydrogenous (H) and deuterated (D) species of a series of isotactic polypropylene blends with various D/H contents has been established for the first time on the basis of the detailed analysis of thermal and infrared spectral data for both α1 and α2 crystalline forms, where the α1 form is the crystal form of disordered chain packing mode but the α2 form has the ordered chain packing structure. The melting point has been found to shift continuously towards higher temperature side with an increase in the H component. This continuous change in the melting and crystallization point was reasonably interpreted by assuming the coexistence of D and H chain stems in the crystal lattice. The so-called correlation splitting was detected as doublets of the infrared bands for the pure D species sample at around 1066 cm−1. This correlation band splitting width changed systematically depending on the D/H ratio and became a singlet for the sample with only 5 mol % D component. This systematic change in the splitting width of the infrared bands can be interpreted also reasonably based on the concept of the random existence of D and H chain stems in the crystal lattice. Although the details of the thermal behavior and the infrared band splitting are different between the α1 and α2 forms, the observed phenomena are essentially the same each other. Both of thermal and infrared data indicate reasonably the cocrystallization phenomenon of the D and H chain stems in the crystal lattice of the α1 and α2 forms when cooled from the melt, suggesting a possibility of the random chain folding mode in the crystalline lamellae.