The two major components of polyurethane formulations are a polyol component and an isocyanate component. Polyether polyols and polyester polyols have been used as the polyol component in polyurethane formulations for many decades. They remain the most commonly used polyols. Vast numbers of polyether polyols and polyester polyols, optimized to provide different combinations of behavior during fabrication processes and performance characteristics of fabricated articles, are available from many different manufacturers.
More recently, polycarbonate polyols have been gaining increasing interest and use in polyurethane formulations, either by themselves or more often in mixtures with selected polyether polyols or polyester polyols, because of their many attractive attributes. These attributes include performance benefits resulting from the high-density polycarbonate backbone. Furthermore, polycarbonate polyols are based on carbon dioxide (CO2), and sequester CO2 directly in their backbones, enhancing the sustainability of polyurethanes.
The images shown in this post are reproduced from product literature by Novomer which is a leading supplier of polycarbonate polyols.
The following reaction scheme shows how CO2 is sequestered in the backbone of a polycarbonate polyol by reaction with an epoxide during synthesis. Many different “R” groups can be used, to provide a broad range of polycarbonate polyol molecular structures.
The functionality of a polycarbonate polyol can also be chosen as desired, by using any one of many different possible starting molecules. For example, the choices of the following three starting molecules produces, from left to right, a diol, a triol, and a tetrol.
Flexible polyurethane foams possessing significantly improved compression force deflection (CFD), tensile strength, tear strength, and energy absorbance were obtained, while keeping the formulation viscosity manageable, by mixing 10% to 25% by weight of a polycarbonate polyol with a polyether polyol.
Rigid polyisocyanurate panel foams with better blowing efficiency (and hence smaller density when using the same concentration of the blowing agent pentane) and smaller cell sizes were obtained, while keeping the formulation viscosity manageable, by mixing 25% to 70% by weight of a polycarbonate polyol with a polyester polyol.
The research summarized in the two paragraphs above was among the earliest work reported in the open literature on the use of polycarbonate polyols in mixtures with polyether polyols or polyester polyols to obtain polyurethane products with improved performance attributes. Much further work has been done in the field since then. Some of this work has been reported in the open literature while much of it has remained secret.
A recent article discussed the use of polycarbonate polyols to produce polyurethane elastomers and elastic polyurethane foams. It also emphasized the use of polycarbonate polyols as a method for sequestering CO2 by immobilizing it in a polymer structure. The diol chain extenders butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, and dipropylene glycol were used along with the polycarbonate diols. Elastomers and semi-rigid foams with excellent performance characteristics were obtained. The performance characteristics could be varied over broad ranges to meet different needs by varying the formulation. For example, the densities of the semi-rigid foams produced in these experiments varied from 0.147 g/cm3 to 648 g/cm3, while the Shore A hardness varied from 30 to 90, and these two properties could be varied independently rather than changing in lockstep with each other.