Polymer Polyols
Polymer polyols are specific polymers commonly used in the production of flexible polyurethane foams and polyurethane elastomers. These special polymers, which are synthesized as stable dispersions of solid polymers (for example, vinyl polymers or copolymers) in polyols, provide many advantages such as increasing the polyurethane open cell structure, improving mechanical properties, and increasing hardness of polyurethane foams [1-5]. The physical and mechanical properties of the polyurethane can be controlled by adding polymer polyols in various proportions to the polyurethane formulation. It is possible to increase the load bearing ability and elasticity of polyurethane by using 10-20 % (wt.) polymer polyol in polyurethane production. The production of polyurethane products with reduced surface defects and long service life is achieved with the use of polymer polyols [4].
Commercial polymer polyols are generally polyether polyols containing styrene-acrylonitrile (SAN) copolymer. Polymer polyether polyols are white, viscous dispersions with good phase stability with a solid concentration of 10-50 % (wt.) of SAN copolymer in a polyether polyol [1-3]. Polyether-based polymer polyols are produced by radical polymerization of one or more unsaturated (vinyl) monomers (styrene, acrylonitrile, etc.) in liquid polyether in the presence of an initiator (for example, azoisobutyronitrile (AIBN), peroxides or percarbonates) [1,2].
"The median diameter of solid particles ( of vinylic polimer) for a polymer polyol is generally less than 1 μm, usually 0,2–0,5 μm" [1]. Process parameters such as reaction temperature, reaction time and mixing speed are important in order to form fine solid particles of desired size and to ensure dispersion stability. In addition, polyol-monomer ratio, monomer type and concentration, initiator type, chain transfer agent concentration are significant parameters in the efficiency of the production process [2,3].
Polyester-based polymer polyols are other specific polymers used in the production of polyurethane. Polyester-based polymer polyols are used in the production of microporous polyurethane elastomers in the production of shoe soles. It is possible to obtain higher hardnesses for the same density product by using polyester polymer polyols, compared to polyurethanes produced without the use of polymer polyols [5].
Polyester-based polymer polyols are obtained by radical polymerization of vinyl monomers in standard polyester. Although polyester-based polymer polyols are less preferred due to their high viscosity and low dispersion ability compared to polyethers, there is an increasing interest in their industrial production due to their better mechanical properties compared to polyether-based polyurethane systems [5].
Evoco Polymer carries out R&D studies on the development of polymer polyols to be evaluated in different application areas.
References
[1] Ionescu, M., Chemistry and Technology of Polyols for Polyurethanes, 2nd Edition, Volume 1, Smithers Rapra Technology Ltd, Shropshire, UK, 2016.
[2] Glowinska, E., Datta J., Romero J. F. R., Herrero D. S., Carmona M., Novel cast polyetherurethanes based on dispersed polymeric polyols, Polymer Testing 68 (2018) 340–349.
[3] Guo R., Lu X., Hua M., Fang D., Yao K., Separation and characterization of poly(styrene-co-acrylonitrile)-graft-poly(propylene oxide) polymer stabilizer formed in dispersion polymerization of styrene and acrylonitrile in polyether, Polym Int 50: 1379-1383 (2001).
[4] Eganov R. V., Sevast’yanov A. V., Efremova A. A., Garipov R. M., Preparation of Polymer Polyols on the Basis of Laprols and Studies of Their Properties, Polymer Science, Series D. Glues and Sealing Materials, 2013, Vol. 6, No. 3, pp. 181–185.
[5] Nefzger H., Bauer E., Michels E., Polymer Dispersions in Polyester Polyols, US Patent 7772321 B1 (2010).
Authors: Duygu Kahraman Date: August 2022
