CHARACTERIZATION OF POLYETHYLENE GLYCOLS USING DIFFERENTIAL SCANNING CALORIMETRY

The melting behaviour of a range of different molecular weight polyethylene glycol (PEG) samples has been studied using differential scanning calorimetry (DSC). It was demonstrated that the shape of the endotherm was sensitive to the sample particle size, while the heat of fusion and melting points of the samples varied with scanning speed. Using standardised conditions, the PEG samples were solidified from the melt either by controlled cooling at 5 K/h or by immersing the sample in liquid nitrogen. The endotherms obtained indicated that the thermal history may determine both the degree of crystallinity and the crystal form of the polyethylene glycols, as shown by changes in the heat of fusion and melting points respectively. Studies using solid state nuclear magnetic resonance supported the conclusion drawn from the DSC studies. The study has therefore indicated that DSC is a suitable technique for detecting solid state changes in polyethylene glycols, thus facilitating standardisation of these materials.