Investigation of Acrylic Acid at High Pressure Using Neutron Diffraction

Blair F Johnston,Andrew J Urquhart,William G Marshall,Simon Parsons,Iain D H Oswald

doi:10.1021/jp502095n

Abstract

This article details the exploration of perdeuterated acrylic acid at high pressure using neutron diffraction. The structural changes that occur in acrylic acid-d4 are followed via diffraction and rationalized using the Pixel method. Acrylic acid undergoes a reconstructive phase transition to a new phase at ∼0.8 GPa and remains molecular to 7.2 GPa before polymerizing on decompression to ambient pressure. The resulting product is analyzed via Raman and FT-IR spectroscopy and differential scanning calorimetry and found to possess a different molecular structure compared with polymers produced via traditional routes.

Highlights

High-pressure techniques have been successfully employed to investigate the polymorphism of a number of different molecular organic solids.[1−4] The exploration using highpressure techniques allows for a greater range of phase space to be investigated for new polymorphs of materials
This type of interaction has been investigated for its potential stabilizing contribution to the crystalline state by Allen et al.[39]. They showed through the use of the Cambridge Structural Database (CSD) and ab initio molecular-orbital calculations that carbonyl−carbonyl interactions can be comparable to medium-strength hydrogen bonds albeit that they are a little weaker in this case
While the energies calculated from Pixel cannot be broken down into individual interactions, there is a significant contribution from the dispersive component in interaction 2 which is known to contribute to carbonyl−carbonyl interactions

Summary

Introduction

High-pressure techniques have been successfully employed to investigate the polymorphism of a number of different molecular organic solids.[1−4] The exploration using highpressure techniques allows for a greater range of phase space to be investigated for new polymorphs of materials. Pixel calculations of phase I show that by far the most favorable molecule−molecule interaction is, unsurprisingly, between the hydrogen bonded molecules (interaction 1) with the dispersive and Coulombic terms showing the greatest stabilizing contribution (Figure 4a; Table ES2, Supporting Information).

Results

Conclusion