Interactions in poly(ethylene oxide)–hydroxypropyl methylcellulose blends

Abstract

Blends of poly(ethylene oxide) and hydroxypropyl methylcellulose in the form of free films are examined for evidence of specific polymer:polymer interactions. Such interactions might affect the drug release behaviour of compressed matrices incorporating these polymers. The effect of HPMC on the crystallisation of PEO during casting is investigated using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. Fourier transform infra-red (FT-IR) and Raman spectroscopies are used to examine the possibility of a complex between the two polymers. Thermodynamic interaction parameters are calculated for films cast from water and N,N-dimethylacetamide (DMAc) using the Flory–Huggins theory of mixing. The interaction parameter calculated is negative, indicating a miscible blend, and a hydrogen bonding interaction is detected. This hydrogen bonding is less likely to occur in films cast from water than in films cast from DMAc perhaps because residual water can shield the interaction sites. Finally, a transition involving a sharp reduction in heat capacity at high temperatures is reported. This transition is characterised using DSC and FT-IR and Raman spectroscopies, and is interpreted as a further complexing of the polymers.