Microphase Separation and Crystallization in H-BondingEnd-Functionalized Polyethylenes.

Well-defined,crystalline, low molar mass polyethylene PEx(where xis the molar mass 1300and 2200 g mol–1) bearing thymine (Thy) or 2,6-diaminotriazine(DAT) end groups have been synthesized from amino-terminated PE. Eitherdouble-layer or monolayer solid-state morphologies were attained dependingon the nature of the end-group(s). PE1300-NH2, PE1300-DAT, and the equimolar blend PE1300-Thy/DAT-PE1300all organized into double-layer structurescomposed of extended PE chains sandwiched between H-bonding chain-ends.The double-layered morphology arose from the microphase separationof the polar end-groups and the nonpolar PE chains and was frozenby the crystallization of the PE domains. The regularity of the PElamellar stacking was higher for the stronger and more directionalassociated pair Thy/DAT compared with samples of either PE-NH2or PE-DAT. For PE1300-Thy, the mesoscopic organizationwas driven by the crystallization of Thy domains prior to crystallizationof the PE chains, forcing the small proportion of nonfunctionalizedPE chains to segregate and crystallize separately to the PE-Thy chains.The confinement of PE chains between Thy domains lead to a conventionalmonolayer form in which extended PE chains were interdigitated. Thevolume fraction of Thy or DAT end-groups was a key parameter in theorganization in all these systems: the PE crystallinity was higherwith longer PE chains (i.e., a low volume fraction of Thy or DAT units),but the mesoscopic organization of the supramolecular PE was lessregular. [ABSTRACT FROM AUTHOR]