A novel polymorph of glycolide, the precursor to polyglycolic acid, has been observed at 0.6 GPa. Large scale high-pressure production has been performed and the seeds successfully used to aid crystallisation of the polymorph at ambient pressure. PIXEL calculations confirm the metastable nature of the polymorph. Subsequent experiments show that, whilst initially stable for 12 days, this may be a case of disappearing polymorphism.
A breakthrough has
been achieved in improving the efficiency of
solid-state polymerization of acetylenedicarboxylic acid (ADCA). Traditional
solid-state polymerization of ADCA is marked by long exposure times
of γ-radiation (>10 days) and very low yields (around 5.5%).
We have been able to perform a reaction to an n =
8 oligomer, as confirmed by matrix-assisted laser desorption/ionization-time
of flight, in less than 2 min by employing ∼6 GPa of pressure.
We have determined the crystal structure of ADCA on increasing pressure
to (5.2 GPa) to provide insight into the process of polymerization
with Pixel calculations supporting our evaluation of the polymerization
process.
This study details the structural characterization of glycolide-h 4 as a function of pressure to 6 GPa using neutron powder diffraction on the PEARL instrument at ISIS Neutron and Muon source. Glycolide-h 4 , rather than its deuterated isotopologue, was used in this study due to the difficulty of deuteration. The low background afforded by zirconia-toughened alumina anvils nevertheless enabled the collection of data suitable for structural analysis to be obtained to a pressure of 5 GPa. Glycolide-h 4 undergoes a reconstructive phase transition at 0.15 GPa to a previously identified form (II), which is stable to 6 GPa.
MDMA (3,4-methylenedioxymethamphetamine) is a Class A substance that is usually found in a tableted form. It is only observed in one orthorhombic polymorph under ambient conditions. It shows slight positional disorder around the methlyenedioxy ring which persists during compression up to 6.66 GPa. The crystal quality deteriorates above 6.66 GPa where the hydrostatic limit of the pressure-transmitting medium is exceeded. The structure undergoes anisotropic compression with the a-axis compressing the greatest (12% cf. 4 and 10% for the b- and c-axes, respectively). This is due to the pattern of the hydrogen bonding which acts like a spring and allows the compression along this direction.
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