Investigating Polymer Conformation in Poly (Ethylene Oxide) (PEO) Based Systems for Pharmaceutical Applications

The purpose of this work is to investigate the relation of hydration and the degree of crystallinity for poly (ethylene oxide) (PEO) tablets using Raman spectroscopic methods and complementary thermal analysis for pharmaceutical interests. The influence of the tableting process is also investigated by measuring the degree of crystallinity and the melting point of PEO powder and tablets. The hydration of the PEO tablets is performed in different relative (RH) humidity environments and the water uptake and the degree of crystallinity of the tablets are measured by TGA and DSC. The dry and hydrated tablets are investigated by Raman spectroscopy. The low frequency region in the Raman spectrum reflects the degree of crystallinity of PEO. The DSC results show a decrease in the degree of crystallinity by tableting and the hydration process. However, the slight decrease in the degree of crystallinity of PEO does not show significant difference in the low frequency Raman spectra, only a slight broadening of the LAM band, at 280 cm-1, is observed. By measuring the PEO tablet immersed in water the hydration process can be followed in-situ with Raman spectroscopy. With changes from dry (fully crystalline) to wet state (amorphous), changes in band intensity and shape are found at 230 cm-1, 280 cm-1, 363 cm1, 535 cm-1 and 580 cm-1. During hydration, the bands at 230 cm-1 and 363 cm-1 decrease in intensity and the sharp LAM band at 280 cm-1 is replaced by the broad D-LAM band. Among the vibrational bands observed, the band at 363 cm-1 is the most suitable to quantitatively follow the ingress of water into the PEO tablet and the continuous decrease of the degree of crystallinity, due to the least interference of the spectral compounds.