Pressure-induced polymorphism of caprolactam : a neutron diffraction study

Hutchison, Ian and Bull, Craig L. and Marshall, William G. and Urquhart, Andrew J. and Oswald, Iain D.H. (2019) Pressure-induced polymorphism of caprolactam : a neutron diffraction study. Molecules, 24 (11). ISSN 1420-3049

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    Abstract

    Caprolactam, a precursor to nylon-6 has been investigated as part of our studies into the polymerization of materials at high pressure. Single-crystal X-ray and neutron powder diffraction data have been used to explore the high-pressure phase behavior of caprolactam and we have observed two new high pressure solid forms. The transition between each of the forms requires a substantial rearrangement of the molecules and we observe that the kinetic barrier to the conversion can aid retention of phases beyond their region of stability. Form II of caprolactam shows a small pressure region of stability between 0.5 and 0.9 GPa with Form III being stable from 0.9 GPa to 5.4 GPa. The two high-pressure forms have a catemeric hydrogen-bonding pattern compared with the dimer interaction observed in the ambient pressure Form I. The interaction between the chains has a marked effect on the directions of maximal compressibility in the structure. Neither of the high-pressure forms can be recovered to ambient pressure and there is no evidence of any polymerization occurring.

    Author(s):Hutchison, Ian, Bull, Craig L., Marshall, William G., Urquhart, Andrew J. and Oswald, Iain D.H. ORCID: https://orcid.org/0000-0003-4339-9392
    Item type:Article
    ID code:68317
    Keywords:high-pressure single-crystal X-ray diffraction, high-pressure neutron diffraction, phase transitions, intermolecular interactions, energy frameworks, Chemistry, Therapeutics. Pharmacology, Organic Chemistry, Pharmacology (medical)
    Subjects:Science > Chemistry
    Medicine > Therapeutics. Pharmacology
    Department:Faculty of Science > Strathclyde Institute of Pharmacy and Biomedical Sciences
    Depositing user: Pure Administrator
    Date deposited:10 Jun 2019 09:06
    Last modified:21 Jul 2019 01:07
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/68317
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