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Issue 2, 2015
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Molecular mapping of poly(methyl methacrylate) super-helix stereocomplexes

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Abstract

In this study, by using X-ray powder diffraction profiles as blueprints, we successfully mapped the most probable molecular-level structural arrangement of the PMMA super-helix stereocomplexes through molecular dynamic simulations. Molecular-level resolution of the PMMA triple-helix supramolecule was not previously achievable by experimental methods. After constructing molecular models of stereo-regular complexes composed of linear it- and st-PMMAs, our all-atom molecular dynamics simulations identified the stereocomplex structure that best reproduces experimental diffraction profiles and thermodynamic properties as a double helix of isotactic (it-)PMMA with a helical pitch of 1.8 nm and 9 units per turn surrounded by a single helix of syndiotactic (st-)PMMA with an average helical pitch of 0.9 nm and 20 units per turn. The it-/st- complexing stoichiometry in the PMMA triple-helix is therefore 9 : 20. This presents the first all-atom model of the it-/st-PMMA triple-helix stereocomplex that accurately fits experimental X-ray diffraction profiles. In addition, the simulation results revealed the outer st-PMMA helix of the PMMA stereocomplex has a fiber diameter of at least 1.85 nm and adopts a non-ideal helical geometry. Furthermore, through dynamic simulations, surprising new sights into the effect of the structural configuration of the PMMA stereocomplex (i.e., helical pitch and direction, and tilt angle) on the physical properties of their crystal structures were obtained. Those crystal properties include X-ray diffraction profile, packing density, chain–chain spacing, chain width and cohesive energy density.

Graphical abstract: Molecular mapping of poly(methyl methacrylate) super-helix stereocomplexes

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Supplementary files

Article information


Submitted
26 Sep 2014
Accepted
01 Dec 2014
First published
01 Dec 2014

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2015,6, 1370-1378
Article type
Edge Article
Author version available

Molecular mapping of poly(methyl methacrylate) super-helix stereocomplexes

A. J. Christofferson, G. Yiapanis, J. M. Ren, G. G. Qiao, K. Satoh, M. Kamigaito and I. Yarovsky, Chem. Sci., 2015, 6, 1370
DOI: 10.1039/C4SC02971B

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