Process making polymer polyol having monodisperse dispersed polymer particles
Polymer polyols are made in a seeded process, in which styrene and acrylonitrile are polymerized in the presence of a base polyol, a seed dispersion and a solvent. The seed dispersion contains an unsaturated macromer. The process produces a polymer polyol in which the dispersed phase particles have a particle size of 1 to 3 μm and a particle size span of less than 1.25. The polymer polyols are very useful for making flexible polyurethane foam for cushioning applications, in which high airflows and good load bearing are needed.
1. A process for making a polymer polyol that contains styrene/acrylonitrile copolymer particles dispersed in a continuous phase that includes at least one polyol, comprising the steps of
a) forming a seed dispersion containing 5 to 25 weight-% of an unsaturated macromer, 2.5-20 weight-% of styrene polymer or copolymer particles having a particle size of 50 to 500 nm, and 55-92.5 weight-% of a seed dispersion carrier polyol, the weight-percentages being based on the weight of the seed dispersion;
b) forming a carrier mixture containing the seed dispersion, a base polyol and a solvent, and dispersing a monomer mixture that includes at least 25 weight-% styrene and greater than 20 weight-% acrylonitrile, based on the weight of the monomer mixture, into the carrier mixture, wherein
i) the amount of seed dispersion is sufficient to provide 0.025 to 0.35 weight percent seed particles and 0.1 to 0.75 weight percent of unsaturated macromer based on the combined weight of the carrier mixture and monomer mixture;
ii) the weight of the monomer mixture is at least 200 times the weight of the seed particles and when polymerized is sufficient to provide the polymer polyol with at least 30 weight-percent dispersed polymer particles and
iii) the amount of the solvent is 6 to 20% of the combined weight of the carrier mixture and the monomer mixture
c) polymerizing the dispersed monomer mixture to form polymer particles dispersed in the carrier mixture and then
d) removing the solvent from the carrier mixture to form a polymer polyol product containing at least 30 weight-percent dispersed polymer particles, wherein the dispersed polymer particles have a particle size of 1 to 3 μm and a particle size span of less than 1.25.
2. The process of claim 1 , wherein the solvent is one or more of an aromatic hydrocarbon, an aliphatic hydrocarbon or a monoalcohol.
3. The process of claim 2 , wherein the solvent includes isopropanol.
4. The process of claim 2 , wherein the amount of monomer mixture is 200 to 500 times the weight of the seed particles.
5. The process of claim 4 , wherein the amount of seed dispersion is sufficient to provide 0.1 to 0.25 weight percent seed particles.
6. The process of claim 5 , wherein the particle size of the seed particles is 75 to 150 nm.
7. The process of claim 5 , wherein the seed dispersion is prepared by homopolymerizing or copolymerizing styrene in the presence of the seed dispersion carrier polyol, the macromer and 5 to 20 weight-% of a solvent.
8. The process of claim 5 , wherein the polymer polyol product contains 35 to 55 weight percent dispersed polymer particles.
9. The process of claim 5 , wherein the amount of solvent present in step b) is 6 to 16 weight-%, based on the combined weight of the carrier mixture and the monomer mixture.
10. The process of claim 5 , wherein the base polyol is one or more polyether polyols having a hydroxyl equivalent weight of 400 to 2500.
11. The process of claim 2 , wherein step c) is performed under sufficient pressure to prevent the solvent from volatilizing.
12. The process of claim 6 wherein the amount of seed dispersion is sufficient to provide 0.1 to 0.5 weight percent of unsaturated macromer based on the combined weight of the carrier mixture and monomer mixture.