The Ends Control the Means

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Science  02 Mar 2012:
Vol. 335, Issue 6072, pp. 1020
DOI: 10.1126/science.335.6072.1020-b

Changing the balance of weak intermolecular forces can change the types of phases that molecules form. Cortese et al. explored the ordering of polypropylene (PPO) oligomers (either 460 or 2200 g/mol) bearing either thymine (Thy) or diaminotriazine (DAT) end groups, as well as mixtures of these molecules. The better-defined hydrogen bonding complementarity of Thy caused those associated oligomers to arrange in both a crystalline phase and a lamellar phase, in which the Thy groups formed an ordered two-dimensional crystal but the PPO chains were disordered. In contrast, DAT-terminated oligomers formed only glasses; the stronger affinity of PPO for DAT than Thy and the multiple hydrogen bonding motifs provided less driving force for microphase separation. In mixtures of the oligomers, the stronger Thy-DAT versus Thy-Thy interactions actually disrupted the lamellar ordering. In these systems, the ability of the end groups to crystallize appeared to be the main driver of mesoscopic ordering.

J. Am. Chem. Soc. 134, 10.1021/ja2119496 (2012).

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