Bio-Based, Self-Condensed Polyols

A new method for the synthesis of high-molar-mass (MM), bio-based polyols for elastic polyurethanes is developed. This process is based on the self-condensation of low MM polyols (M-n approximate to 1000) and vacuum removal of the resulting glycerol. Self-condensation products are hyperbranched estolide polyols with average MMs close to 3000 and hydroxyl numbers in the range of 40-95 mg KOH g(-1). Three polyols, one with primary and two with secondary hydroxyls and different functionalities, are studied. The transesterification proceeded much faster with primary hydroxyls, leading to high-viscosity products. The effect of functionality and reactivity of starting polyols on properties is discussed. Practical applications: The process is useful for upgrading the existing natural oil-based polyols to higher MM, lower OH number and variable-functionality polyols, for expanding application in the urethane field. The process is simple, involving just an oil-based polyol, a catalyst, and heating under vacuum.