MELT DISPERSION PROCESS FOR MAKING POLYMER POLYOLS

Abstract

A preformed thermoplastic polymer is dispersed into a polyol via a mechanical dispersion process. A stabilizer is present to stabilize the dispersed polymer particles. An antisolvent is also present. The antisolvent has been found to lead to smaller particle size and increased dispersion stability.

Claims

1. A method for making a polymer polyol, comprising the steps of: (a) forming a heated and pressurized mixture of i) one or more 250 to 6000 hydroxyl equivalent weight alcohols selected from the group consisting of polyethers having an an oxyalkylene content of at least 80% by weight, polyesters and natural oil polyols, each 250 to 6000 hydroxyl equivalent weight alcohol nominally having 1 to 8 hydroxyl groups per molecule, wherein each such 250 to 6000 hydroxyl equivalent weight alcohol is a liquid at 25° C. and 101.3 kPa atmospheric pressure and has a boiling temperature of at least 150° C. at 101.3 kPa atmospheric pressure; ii) a thermoplastic polymer that is insoluble in component i) and has a Vicat softening temperature of greater than 60° C. and up to 300° C.; iii) a dispersion stabilizer and iv) an antisolvent, the heated and pressurized mixture being at a temperature above the Vicat softening temperature of the thermoplastic polymer and at a pressure sufficient to maintain the antisolvent and component i) as a liquid, (b) shearing the heated and pressurized mixture to form a dispersion of droplets of the heat-softened thermoplastic polymer in a liquid phase that includes the 250 to 6000 hydroxyl equivalent weight alcohol or alcohols and (c) cooling the dispersion of droplets to below the Vicat softening temperature of the thermoplastic polymer to solidify the droplets of the thermoplastic polymer to form particles thereof and form the polymer polyol.

2. The method of claim 1 wherein the mixture formed in step (a) comprises 30 to 75 weight-% of i), 20 to 55 weight-% of ii), 0.5 to 5 weight-% of iii) and 2 to 10 weight-% of iv), the weight percentages being based on the combined weights of i), ii), iii) and iv).

3. The method of claim 1 further comprising (d) simultaneously with and/or after step (c), removing antisolvent from the polymer polyol until the antisolvent content of the polymer polyol is less than 0.5% by weight.

4. The method of claim 3 wherein after step (d) the polymer polyol contains 35 to 55% by weight of dispersed particles of the thermoplastic polymer.

5. The method of claim 1, wherein the stabilizer includes a copolymer of (1) from 10 to 40% by weight of a branched polyol having a molecular weight of from 4000 to 20,000, at least one polymerizable ethylenically unsaturated group per molecule and from about 3 to about 8 hydroxyl groups per molecule with (2) from 60 to 90% by weight of styrene or a mixture of styrene and one or more other low molecular weight monomers.

6. The method of claim 1 wherein the antisolvent includes water.

7. The method of claim 1 wherein component i) is one or more polyether polyols.

8. The method of claim 1 wherein component ii) is polystyrene or a styrene-acrylonitrile copolymer.

9. A polymer polyol made in accordance with claim 1.

Description

EXAMPLES 1-2 AND COMPARATIVE EXPERIMENTS A AND B

A. Production of Macromer

[0073] Potassium hydroxide is added to a sorbitol-initiated poly(propylene oxide) starter polyol having a weight average molecular weight of about 700. Enough of the potassium hydroxide is added to provide about 2100 ppm KOH in the final product. An 88/12 mixture of propylene oxide and ethylene oxide is added and allowed to polymerize at a temperature of 105° C. to produce a hexafunctional polyol in which propylene oxide and ethylene oxide are randomly polymerized. The final ratio of propylene oxide and ethylene oxide is about 88.5:11.5 by weight. The final hydroxyl number is about 28, which corresponds to a hydroxyl equivalent weight of 2003 and a number average molecular weight of about 12,000. The oxyalkylene content is about 98.4% as calculated from the starting materials. After finishing and addition of 250 ppm antioxidant, 500 parts of this copolymer are heated to 55° C. with stirring and 0.55 moles of TMI (per mole of copolymer) are added. Then 0.05 of a tin catalyst are added, and the mixture is stirred at 55° C. for 120 minutes. The product (Macromer Mixture A) of this reaction is a mixture containing about 55% by weight of a macromer corresponding to the reaction product of TMI and the polyether and about 45% by weight of uncapped polyether. The macromer molecules contain 1-2 polymerizable carbon-carbon double bonds per molecule and 4-5 hydroxyl groups per molecule.

B. Preparation of Stabilizer Mixture

[0074] 120 parts of Macromer Mixture A are charged to a reactor equipped with a pump inlet and a stirrer. The headspace is purged several times with nitrogen and padded with nitrogen. The reactor is sealed and it and its contents are heated to 120° C. With agitation and while keeping the reaction temperature at 120° C., there is added over 2 hours a mixture of 160 parts by weight styrene, 0.96 parts of a free radical initiator and 519 parts of a Polyol A (a 4600 molecular weight, 36 hydroxyl number polyol made by adding propylene oxide and then 20.3% based on total polyol weight of ethylene oxide onto glycerin). After this mixture is added, agitation is maintained as the temperature is increased to 150° C. over three hours, followed by holding that temperature for 1 hour and then cooling to 40° C. The resulting Stabilizer Mixture contains about 28% by weight of a copolymer of styrene and the macromer formed in step A (the dispersion stabilizer) and 72% by weight of polyether polyols (Polyol A plus the amount of uncapped polyether from step A). The Stabilizer Mixture contains about 20% polymerized styrene.

C. Preparation of Polymer Polyols

[0075] Comparative Sample A: 28 parts of the Stabilizer Mixture from step B, 35 parts of a polystyrene having a Vicat softening temperature of about 103° C. and a number average molecular weight of 40,000 g/mol, and 37 parts of Polyol A are loaded into a Parr reactor equipped with a Cowles blade. The reactor is closed and pressurized to 400 psig (2.75 MPa). The reactor contents are heated to 220° C. and held at that temperature for 20 minutes, and then cooled to room temperature, with constant agitation. The Cowles blade is rotated at a speed of 60 rpm until the temperature reaches 180° C., at 500 rpm when until the temperature reaches 220° C., at 1000 rpm until the temperature returns to 180° C., at 500 rpm until the temperature returns to 100° C. and thereafter at 60 rpm. The higher agitation rates are sufficient to shear the mixture to form a dispersion of polystyrene particles in Polyol A.

[0076] The resulting polymer polyol contains 35% by weight of the polystyrene, about 7.84% by weight of the dispersion stabilizer and the remainder polyether polyols (Polyol A plus uncapped polyether from step A above). The dispersed polystyrene particles have a volume average particle size of 13.6 μm (as measured with a BeckmanCoulter Micro Liquid Module laser diffraction particle size measurement instrument after diluting the sample with isopropanol). The polymer polyol has a Brookfield viscosity (20 rpm, #4 spindle, 25° C.) of 6180 mPa.Math.s.

[0077] Example 1: Comparative Sample A is repeated, adding 5 parts of water into the Parr reactor prior to closing the reactor and heating its contents. The pressure conditions are sufficient to maintain the water in liquid form throughout the process. Water is removed from the product via rotary evaporation until the water content is reduced to less than 0.05% by weight, based on total product weight. The dispersed particles in the resulting polymer polyol has a volume average particle size of 5.8 μm. The polymer polyol has a Brookfield viscosity of 3480 mPa.Math.s. The addition of water into the mechanical dispersion process results in a decrease in both particle size and product viscosity.

[0078] Comparative Sample B: Polystyrene as described in previous examples is fed at a rate of 35 parts per hour into the inlet end of a twin-screw extruder having a L/D ratio of 60 and multiple heating zones. The temperatures in the heating zones increase from 30° C. to 200° C. Screw speed is 1000 rpm. The screw is equipped with gear mixer elements to facilitate mixing of the high viscosity heat-softened polystyrene into the much lower viscosity Polyol A. In a downstream section, at which the polystyrene has become heat-softened, 28 parts per hour of the Stabilizer Mixture from Step B and 35 parts per hour of Polyol A are added through separate injection ports. Pressure in the extruder is maintained at 650 psig (4.5 MPa). The heat-softened polystyrene is sheared into small droplets that become dispersed in Polyol A, which forms a continuous phase. The resulting dispersion is collected from the outlet end of the extruder and cooled to room temperature in a stirred vessel. It contains 35% by weight of the polystyrene, about 7.84% by weight of the dispersion stabilizer and the remainder polyether polyols (Polyol A plus uncapped polyether from step A above). The dispersed particles have a volume average particle size of 4.0 μm (as measured with a BeckmanCoulter Micro Liquid Module particle size measurement instrument after diluting the sample with isopropanol). The dispersion has a Brookfield viscosity of 7400 mPa.Math.s. This continuous extrusion process produces a smaller particle size product than the batch process of Comparative Sample A, but the product viscosity is significantly higher.

[0079] Example 2: Comparative Sample B is repeated, adding 5 parts per hour of water. The water is injected through the same injection port as the Stabilizer Mixture from Step B. The pressure conditions within the extruder are sufficient to maintain the water in liquid form. After the extruded product has cooled to room temperature, water is removed using a rotary evaporator until the water content of the product is less than 0.05% by weight. The resulting polymer polyol has a volume average particle size of 3.4 μm (as measured with a BeckmanCoulter Micro Liquid Module particle size measurement instrument after diluting the sample with isopropanol), and a Brookfield viscosity (of 6400 mPa.Math.s.

[0080] Compared with Comparative Sample B, the addition of the water results in a significant reduction in particle size and in product viscosity.