Structure formation in nanophase-separated systems with lamellar morphology: Comb-like vs. linear precision polymers

Abstract

We report findings of a comparative study of a comb-like polymer, poly(1,4-phenylene-2,5-n-didecyloxy terephthalate) [PPDOT] and a linear chain precision polymer consisting of a methyl protected 2,6-diaminopyridine group after every 20th methylene unit of a linear saturated polyethylene chain [PDAPS20]. Both polymers exhibit lamellar morphologies related to a nanophase separation of the methylene sequences from ring-like sub-units as seen in X-ray diffraction data. Although their chain architecture is different, investigations on oriented samples of both PPDOT and PDAPS show that their lamellae orient in such a way that their surface normals tend to be perpendicular to the shear fields leading to different average chain orientations. A novel approach considering the volume occupied per CH2 unit in the alkyl nanodomain calculated on the basis of unit cell considerations is employed to understand the packing state of the alkyl segments. While modification B of PPDOT exhibits densely packed alkyl nanodomains, modification A of PPDOT and PDAPS20 show a relatively loose packing. At the end, we attempt to bring together these two classes of polymers exhibiting nanophase-separated morphologies by means of a classification scheme based on the structural arrangement of the sub-units within their respective domains, highlighting their similarities and differences.