Differential scanning calorimetry: Prior to analysis by DSC, all samples were dried overnight under vacuum at 50 °C. Approximately, 10 mg of material was weighed into an aluminium DSC pan and sealed non-hermetically with an aluminium lid. The sample pan was then loaded into a Mettler Toledo DSC1. The sample and reference were heated from -150 to 150 °C at a scan rate of 10 °C min -1 and the resulting heat flow response was monitored. The sample was re-cooled to -150 °C and then reheated again to 150 °C, all at 10 °C min -1 . Nitrogen was used as the purge gas, at a flow rate of 150 mL min -1 .