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

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 wa...

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Bibliographic Details
Published in:Chemical science (Cambridge) 2015-01, Vol.6 (2), p.1370-1378
Main Authors: Christofferson, Andrew Joseph, Yiapanis, George, Ren, Jing Ming, Qiao, Greg Guanghua, Satoh, Kotaro, Kamigaito, Masami, Yarovsky, Irene
Format: Article
Language:English
Subjects:
Chains
Chemistry
Computer simulation
Diffraction
Helical
Isotactic
Molecular dynamics
Polymethyl methacrylates
Stereocomplexes
X-rays
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Summary: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 ( , 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.
ISSN:2041-6520
2041-6539
DOI:10.1039/c4sc02971b