Raman spectroscopy investigation of mono- and diacyl-polyoxyethylene glycols

Physical and thermal properties of polyoxyethylene glycol glycerides (Gelucire 50/13) used as sustained release matrix forming agent in pharmaceutical applications are studied by Raman spectroscopy combined with X-ray diffraction and differential scanning calorimetry methods.At first, Raman spectroscopy was used to characterize the polymorphs and liquid state of PEG 1500, with emphasis placed on the evolution of the Raman-active CC and CO stretching region (1300–1100 cm⁻¹), along with complementary analysis of the Raman-active CH stretching modes (3000–2800 cm⁻¹) in comparison with temperature. Unique Raman signatures were obtained for all phases, with their identity confirmed using DSC and XRD. The CC and CO stretching modes, which provided insight into the trans/gauche content, permitted polymorph discrimination due to differences in the number of modes, their relative frequencies and their full-widths at half-maximum. CH stretching generally increased with polymorph stability, indicating the dominance of methylene antisymmetric CH₂ vibrations as the PEG 1500 crystal lattice became more ordered. The change in the intensities of the CH stretching bands was used to probe the order–disorder transition.The second time, Raman spectroscopy of Gelucire 50/13 was performed to characterize the contribution of its each component, with emphasis placed on the evolution of the t(CH₂) and ν(CC) vibrational mode regions (1300–1200 cm⁻¹), along with analysis of the Raman-active CH stretching modes (3000–2800 cm⁻¹), δ(CH₂) and δ(CH₃) deformation region (1500–1400 cm⁻¹), and r_as(CH₂) rocking region (900–800 cm⁻¹). In comparison with temperature, the changes of the ratios of Iν_s(CH₂)]/Iν_as(CH₂)] (I₂₈₅₀/I₂₈₉₀), Iν_as(CH₂)]/Iν_s(CH₃)] (I₂₈₉₀/I₂₉₅₀), Iδ(CH₂)]/Iδ(CH₃)] (I₁₄₄₄/I₁₄₉₀), I₁₂₉₆/I₁₂₈₂ and Ir_as(CH₂)]/It(CH₂)] (I₈₄₅/I₁₂₈₂) were directly correlated with conformational changes of the Gelucire structure. Overall, Raman spectroscopy clearly demonstrated that the different functional groups studied could be characterized independently, allowing for the understanding of their role in Gelucire polymorphism.