Polymorphism of glyceryl ethers and ether esters

Abstract

AbstractPhase behavior has been studied by thermal and diffraction methods for 1‐and 2‐palmityl and stearyl ethers of glycerol and for 14 trialkyl glyceryl ethers, dialkyl monoacyl glyceryl ethers and monoalkyl diacyl glyceryl ethers, all of which were saturated trichain substituted glycerol compounds containing one or more of the following chains: palmityl (Py), palmitoyl (P), stearyl (Sy) and stearoyl (S). The monoalkyl glyceryl ethers resemble monoglycerides in crystallization behavior but with significant differences. Isomeric 1‐ and 2‐ethers are very close in melting point. The 1‐ethers show, besides a stable form, two other forms which transform reversibly to each other. The 2‐ethers are polymorphic but with only one clearly established melting level. All trichain compounds were polymorphic also, most being dimorphic, each exhibiting a metastable α form, typically more stable than that of related triglycerides. Forms other than α were labeled I, II, etc., in order of decreasing melting point and were typically obtained from solvent. Polymorphic behavior showed some rather large departures from that of related triglycerides and appeared generally more sensitive to impurities. The two triethers, PyPyPy and SySySy were dimorphic each with a stable form much resembling metastable α in diffraction pattern, hence presumed to be of a new (more dense) hexagonal type of cross sectional structure. Three dialkyl monoacyl compounds PyPyP, SySyS and SyPyS and also three monoalkyl diacyl compounds PPyP, SSyS and SPyS were dimorphic, with Form I a stable, nontilted, somewhat β′‐like form. PySyS and PSyP, which were trimorphic, showed such a β′‐like form as a Form II, i.e., a second highest melting point. The stable phase of four compounds, namely PyPP, SySS, PySyS (all trimorphic) and dimorphic PySS (and possibly that of SyPP) could be called a β phase. Presence of an alkyl group on the 2 position of glycerol, in all but the PySyS, prevented β structure. PSyP and SyPP exhibited triple chain length structures, not encountered in saturated mixed triglycerides with less than four carbons difference in the acyl chains. SyPP was exceptional in showing four forms.