Structure Analysis and Derivation of Deformed Electron Density Distribution of Polydiacetylene Giant Single Crystal by the Combination of X-ray and Neutron Diffraction Data

Abstract

The crystal structure of polydiacetylene giant single crystal has been analyzed on the basis of the two different methods of wide-angle neutron diffraction and X-ray diffraction. The X-ray result gives us the total electron density distribution [ρ(x)] of polymer chain. The neutron result tells the positions of atomic nuclei, which can allow us to speculate the electron density distributions [ρ 0(x)] around the nonbonded isolated atoms. As a result, the so-called bonded (or deformed) electron density Δρ­(x) [≡ ρ­(x) – ρ0(x) = ρX(x) – ρN(x)], i.e., the electron density distribution due to the conjugation among the covalently bonded atoms along the polymer chain, can be estimated using the two information obtained by the X-ray and neutron data analyses (the so-called X-ray–neutron subtraction (X–N) method). The present report is the first example of the application of X–N method to the synthetic polymer species. The Δρ­(x) derived for polydiacetylene was found similar to that of the low-molecular-weight model compound having the similar electronically conjugated chemical formula. The Δρ­(x) was calculated by the density functional theory, which was in a good agreement with the experimental result qualitatively.

Deciphering the 3D Microstructures of a Doubly Charged Homopolymer through a Complementary Correlation of Monomer Crystallography and Polymer Powder X-ray Diffraction

“…The vinyl groups of the monomer single-crystal are aligned appropriately with an interatomic distance of 5.831(10) Å to allow polymerization to occur parallel to the a -axis. Solid-state polymerization is a well-known phenomenon that occurs within the monomer single crystal upon photoirradiation. − …”

Introduction of Disorder in the Crystal Structures of Atactic Poly(vinyl Alcohol) and Its Iodine Complex To Solve a Dilemma between X-ray and Neutron Diffraction Data Analyses

“…The thus-obtained TOF data were converted into the 2D reciprocal lattice images. The details of the experimental system are described in refs. ,− …”

“…If a so-called giant single crystal of a synthetic polymer is obtained luckily, quite an accurate crystal structure can be obtained because of the successful collection of several thousands of sharp spots. The typical case is seen in the photoinduced solid-state polymerization reaction of a single crystal of monomer species. − However, they are quite special cases. At present, we focus on the general synthetic polymers.…”

“…In this way, the combination of X-ray and neutron diffraction methods may be one of the most useful techniques to obtain the reliable crystal structure of a synthetic polymer. However, the actual challenge in using these two methods in an organized manner has not been reported much in the literature. ,− We reported some case studies about the crystal-structure analysis of several kinds of polymer substances based on wide-angle neutron diffraction (WAND) data: orthorhombic polyethylene, trigonal polyoxymethylene, poly­(ethylene oxide), poly­( l -lactic acid), and so on . As will be described in the present paper, we have treated a uniaxially oriented deuterated atactic poly­(vinyl alcohol) ( at -PVA) and its iodine complex to measure both the X-ray and neutron diffraction data.…”

Hybridization of Wide-Angle X-ray and Neutron Diffraction Techniques in the Crystal Structure Analyses of Synthetic Polymers

“…In a case, we may know the atomistic mechanical deformation mechanism of polymer chain subjected to a tensile force [ 41 ]. In a luckier case, we can extract the information of the electron density distribution by combining the WAXD and WAND data [ 42 ].…”