Polymorphic transformations in sn‐1, 3‐distearoyl‐2‐ricinoleyl‐glycerol

Polymorphic transformations of sn‐1,3‐distearoyl‐2‐ricinoleyl‐glycerol (SRS) have been studied with differential scanning calorimetry, X‐ray powder diffraction (XRD), synchrotron radiation X‐ray diffraction, and Fourier transform infrared spectroscopy (FTIR) techniques by using a 99.8% pure sample. Four polymorphs, α, γ, β′2, and β′1, were isolated. The thermal behavior of the four forms showed that the fusion of α at 25.8°C was followed by the crystallization of γ which melts at 40.6°C, and β′2 and β′1 revealed melting peaks at 44.3 and 48.0°C, respectively. No β form was observed, even when the two β′ forms were annealed around their melting points over one week. The XRD long spacing indicates that α packs into a double chain‐length structure; however, γ and the two β′ phases pack into a triple chain‐length structure. The polarized and nonpolarized FTIR spectra in methylene scissoring and methylene rocking regions indicated a parallel subcell packing in γ, and a mixture of orthorhombic perpendicular and parallel or hexagonal subcells in the β′2 and β′1 phases. Consequently, SRS exhibits quite a unique polymorphic behavior, compared to tristearoyl glycerol and sn‐1,3‐distearoyl‐2‐oleoyl‐glycerol.