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 CH 2 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.