Solution-grown crystals of precise acid- and ion-containing polyethylenes

Abstract

Crystals of precise acid- and ion-containing polyethylenes were prepared from solution. While large pendant groups on polyethylene backbones are typically excluded from the crystalline domain, the precisely-placed acid and ionic functional groups are accommodated into the solution-grown crystals. Polyethylene containing carboxylic acid pendant groups on every 21st carbon atom (p21AA) grows into rectangular shaped crystals with an average thickness of 9 nm, which is 3–4 times the all-trans chain length between the functional groups. This thickness indicates that the carboxylic acid groups are incorporated within the crystals. Electron diffraction images and Raman spectra indicate that p21AA backbones are hexagonally packed with more gauche chain conformations than the polyethylene orthorhombic phase. The precise polyethylene containing geminal carboxylic acid groups placed every 21 carbon atoms (p21gAA) forms irregular-shaped crystals with an average thickness 8 nm. Similar to p21AA, p21gAA incorporates the geminal acid groups into its solution-grown crystals. Surprisingly, the polymer with imidazolium bromide groups on every 21st carbon (p21ImBr) produces remarkably large crystals with thicknesses of 200–900 nm, and widths of 6–12 μm. Finally, we propose a multi-layer stack of adjacent reentry structures that is consistent with the incorporation of large functional groups into the solution-growth crystals of these precise polyethylenes. Interestingly, this stacked structure is distinct from our recent results in melt-crystallized p21AA, where the layers are nearly transverse to the lamellae.