The polymerization pathways of epoxidized and hydroxylated triglycerides with phosphoric acid (H3PO4) were investigated using model reactions. Involved epoxides and diols were derived from oleic acid methyl ester, which was easily monitored by one- and two-dimensional nuclear magnetic resonance (NMR) techniques as well as electrospray ionization mass spectroscopy (ESI-MS). Phosphoric acid played two key functions: (a) as a Brønsted acid catalyst that activated the epoxide toward nucleophilic attack by the diol, thus generating ether (C–O–C) cross-linkages; and (b) as a reaction partner establishing phosphate ester linkages [(RO)2(O)P–O–C, R = C or H]. In studies with 18O labeled diol, phosphate esters formed exclusively from H3PO4 and epoxide without incorporation of diol whereas diols acted as polymerization initiators in polyether formations.
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Ahn et al. (2011) studied this question.