Microphase Separation and Crystallization in H‑Bonding End-Functionalized Polyethylenes

Well-defined, crystalline, low molar mass polyethylene PE x (where x is the molar mass 1300 and 2200 g mol–1) bearing thymine (Thy) or 2,6-diaminotriazine (DAT) end groups have been synthesized from amino-terminated PE. Either double-layer or monolayer solid-state morphologies were attained depending on the nature of the end-group(s). PE1300-NH2, PE1300-DAT, and the equimolar blend PE1300-Thy/DAT-PE1300 all organized into double-layer structures composed of extended PE chains sandwiched between H-bonding chain-ends. The double-layered morphology arose from the microphase separation of the polar end-groups and the nonpolar PE chains and was frozen by the crystallization of the PE domains. The regularity of the PE lamellar stacking was higher for the stronger and more directional associated pair Thy/DAT compared with samples of either PE-NH2 or PE-DAT. For PE1300-Thy, the mesoscopic organization was driven by the crystallization of Thy domains prior to crystallization of the PE chains, forcing the small proportion of nonfunctionalized PE chains to segregate and crystallize separately to the PE-Thy chains. The confinement of PE chains between Thy domains lead to a conventional monolayer form in which extended PE chains were interdigitated. The volume fraction of Thy or DAT end-groups was a key parameter in the organization in all these systems: the PE crystallinity was higher with longer PE chains (i.e., a low volume fraction of Thy or DAT units), but the mesoscopic organization of the supramolecular PE was less regular.