Synthesis of Polyols for the preparation of biodegradable polyurethanes

Abstract

Natural oils such as rapeseed oil do not contain the necessary chemical functionality (hydroxyl groups) required for the synthesis of the target biodegradable Polyurethane. The main aim of this work was to find an appropriate dihydroxylation reaction route to convert natural oils containing double bonds into polyols that can be used to produce biodegradable polyurethanes. We were particularly aiming for a low-cost process which could also be scaled up. Initial experiments were performed on model substrates containing double bonds (hexene and decatriene) to allow complete characterization of the compounds and consequently gain a more thorough understanding of the chemistry taking place. Several methods were investigated to find a suitable process to dihydroxylate alkenes and also to convert the unsaturated oils into polyols suitable for the preparation of polyurethanes. The permanganate and water system was suitable for the model compounds, but requiring a stoichiometriс amount of catalyst was a disadvantage for scale-up. The results of hydroxylation reaction of alkenes using hydrogen peroxide and formic acid were not encouraging. The results of hydroxylation reactions using phosphoric acid and hydrogen peroxide were quite encouraging. The reactions using natural oils were quite successful producing polyols with the hydroxide numbers of 187 and 164 for soyabean and rapeseed samples respectively. The method using organic peroxide, meta-сhlого perbenzoic acid (m-СРВА) was also encouraging. The (^1)Ή NMR analysis of the reaction of m-CPBA with the decatriene model compound revealed that m-CPBA selectively hydroxylates the internal double bonds. However, when natural oils, water and m-CPBA powder were mixed and stirred the reaction mixtures became dough like and were therefore difficult to manipulate.