Journal article
Pressure-induced polymorphism of caprolactam: A neutron diffraction study
University of Strathclyde1
Rutherford Appleton Laboratory2
Department of Health Technology, Technical University of Denmark3
Biotherapeutic Engineering and Drug Targeting, Department of Health Technology, Technical University of Denmark4
Colloids & Biological Interfaces, Biotherapeutic Engineering and Drug Targeting, Department of Health Technology, Technical University of Denmark5
Ocular Drug Delivery, Biotherapeutic Engineering and Drug Targeting, Department of Health Technology, Technical University of Denmark6
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; two new high pressure solid forms were observed.
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 GPa 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 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.
| Language: | English |
|---|---|
| Publisher: | MDPI |
| Year: | 2019 |
| Pages: | 2174 |
| ISSN: | 14203049 and 14315157 |
| Types: | Journal article |
| DOI: | 10.3390/molecules24112174 |
| ORCIDs: | 0000-0002-5170-6674 , 0000-0003-4339-9392 and Urquhart, Andrew J. |
Energy frameworks High-pressure neutron diffraction High-pressure single-crystal X-ray diffraction Intermolecular interactions Phase transitions
Acetates Caprolactam Crystallography, X-Ray Ethanol Models, Molecular Molecular Conformation Neutron Diffraction Organic chemistry Phase Transition Pressure QD241-441 energy frameworks ethyl acetate high-pressure neutron diffraction high-pressure single-crystal X-ray diffraction intermolecular interactions phase transitions
