Cocrystallization Phenomenon between the H and D Species of Isotactic 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.

Determination of Chain-Folding Structure of Isotactic Polypropylene in Melt-Grown α Crystals by 13C–13C Double Quantum NMR and Selective Isotopic Labeling

“…34 As demonstrated above, SS-NMR strategy highly relies on editing ability of spectrum by combined pulse techniques. Highresolution 13 C CPMAS NMR under 1 H decoupling is very sensitive to mobility of polymer chains.…”

Three-Dimensional Conformation of Folded Polymers in Single Crystals

“…Over the past several decades, various experimental techniques such as neutron scattering (NS) [8,9], infrared spectroscopy (IR) [10], decoration approach [11], and atomic force microscopy (AFM) [12][13][14] have been developed and used to characterize the chain-folding (CF) structure of polymers in melt-and solution-grown crystals. Nevertheless, detailed CF structures remain a matter of debate because of experimental limitations.…”

Chain Trajectory, Chain Packing, and Molecular Dynamics of Semicrystalline Polymers as Studied by Solid-State NMR

“…Crystallization of long polymer chains leads to drastic structural change from random coils in the melt and solution states into folded chains in thin crystalline lamellae [1,2,3,4,5]. Much attention has been paid to understand the chain-folding structure of semicrystalline polymers over the last half century, because chain-level structures include specific information regarding when, where, and how long polymer chains change their own structures during crystallization [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]. Thus, characterization of folded chain structure is a particularly important subject to understand the crystallization process, as well as the mechanism at the molecular level.…”

“…Three or four decades ago, neutron scattering (NS) on 2 H/ 1 H polymers indicated that the radius of gyration ( R g ) of polyethylene (PE) crystallized from the melt is close to that in the melt state, and the R g in the solution-grown crystals is much smaller than that in the solution state [7]. Furthermore, local folding structures of PE and other polymers have been investigated by NS [8,9,10,11,12], infrared (IR) [13,14,15], morphological observation by transmission electron microscopy (TEM) via surface decoration by oligomers [16], direct visualization of chains [23,24,25], and force detections of single chain by atomic force microscopy (AFM) [26]. However, there are inconsistent views on the chain-folding patterns because of insufficient experimental resolutions.…”