Crystallization of Polyethylenes Containing Chlorines: Precise vs Random Placement

Abstract

The crystallization behavior and crystalline structure of a series of chlorine-containing polyethylenes (PEs) with either a random or a precise placement of the Cl atom on each and every 21st, 19th, 15th, and 9th backbone carbon have been studied by DSC, NMR, Raman spectroscopy, WAXD, SAXS and AFM in samples cooled from the melt at 1°C/min. All precision Cl-substituted PEs crystallize as homopolymers based on their DD/MAS solid-state 13 C NMR spectra that reveal a uniform distribution of the content of halogen between crystalline and noncrystalline regions. In addition, unique WAXD crystallographic patterns that differ from those of the linear PE and random polymers, relatively large crystal thicknesses, and sharp crystallization and melting peaks also support this homopolymer pattern in precision systems. In contrast, a high concentration of Cl in the noncrystalline regions in the case of the random systems suggest that the crystallization process for randomly substituted samples is being led by the selection of the most crystalline sequences, resulting in broad thermal transitions and lower crystallinities. Increasing chlorine content in both precision and random systems decreases crystallinity, melting temperature, heat of fusion, and crystallite thicknesses suggesting that Cl atoms are defects that hinder the crystallization of these polyolefins. Both systems are found to exhibit a lamellar crystalline morphology. Precision substituted polyethylenes form long, straight, and stacked lamellae with axialitic (PE21Cl, PE19Cl, and PE15Cl) or spherulitic (PE9Cl) organization as typical of homopolymers of similar molar mass. In contrast, the lamellae of random analogs are curved and more segmented as found in other PE random copolymers. The distribution of Cl within the crystalline regions of systems with precision substitution is strongly affected by the sequence length of the methylene groups. Packing around the substitution point of PE21Cl, PE19Cl, and PE15Cl render nearly all-trans conformations and asymmetric Cl distribution, while close staggering of Cl atoms in the crystals of PE9Cl exert conformational distortions as observed by a strong increase of TG conformers in the Raman spectra.

Dynamics of Precise Ethylene Ionomers Containing Ionic Liquid Functionality

“…21 The presence of the polar ImBr side groups, even when precisely spaced, disrupts the ability of these materials to crystallize and slows crystallization considerably. As expected, ionomers with longer ethylene spacer lengths (decreasing ion content) lead to slightly higher degrees of crystallinity (X c ) and melting temperatures.…”

Heterogeneous Coordination Environments in Lithium-Neutralized Ionomers Identified Using 1H and 7Li MAS NMR

“…The precise PE ionomers have been extensively characterized using X-ray scattering, scanning electron microscopy, NMR [7,12]. The crystallization and segmental dynamics as a function of random versus precise functional group spacing has been probed using 13 C, 19 F and 31 P MAS NMR [7,8,13,14], high-speed 1 H MAS NMR [15], and static 2 H NMR [9]. For the present study, characterization of the heterogeneous carboxylic acid proton environments observed for both the precise and random P(E-AA) materials is of interest.…”

Criss‐cross amphiphilic polymers and analogous model systems

“…demonstrated that the folding behavior of polyethylene‐like polymers can be controlled by placing bulky substituents at periodically along the polymer backbone, which served as a folding controller . Similarly, research groups of Wagener, Winey, Mecking, and others studied folding of polyethylene‐like chains by periodic placement of hexyl, oligoethylene glycol, sulfonate or even chloro‐ substituents, along the backbone . They also demonstrated the profound effect of periodicity of the substituent on the folding behavior and the lamellar dimensions; in case of randomly distributed branch points, the polymers were found to exhibit curved and segmented morphologies .…”