Ethylene oxide/propylene oxide polyether polyols and polyurethanes made therefrom

Abstract

Copolymers of propylene oxide and ethylene oxide have an inner block that contains from 65-90 weight percent oxyethylene units and from 10 to 35 weight percent oxypropylene units. This block has a molecular weight of from 150 to 350. The copolymer has an outer block which contains at least 95 weight % oxypropylene units and from 0 to 5% oxyethylene units. The equivalent weight of the copolymer is from 800 to 2000. The copolymers are useful in making polyurethane foams that have unexpectedly high tensile and/or tear strengths.

Claims

1. A process for making a polyurethane foam comprising forming a foam formulation containing at least (a) one or more polyether polyol(s) having a hydroxyl equivalent weight of from 800 to 2000, wherein at least 60% by weight of the one or more polyether polyol(s) is one or more propylene oxide/ethylene oxide copolymers containing two or more hydroxyl-terminated polyether chains extending from the residue of an initiator compound, wherein the two or more hydroxyl-terminated polyether chains each contain an inner block and an outer block, each inner block having a molecular weight of from about 150 to 350 and containing from 10 to 35% by weight of oxypropylene units and from 65 to 90% by weight of oxyethylene units, and each outer block containing from 95 to 100% by weight oxypropylene units and from 0 to 5% by weight oxyethylene units, and further wherein the one or more propylene oxide/ethylene oxide copolymers have a hydroxyl equivalent weight of from 800 to 2000 and a total oxyethylene content of from 5 to 18% by weight; (b) at least one blowing agent; (c) at least one organic polyisocyanate; and (d) at least one surfactant and at least one catalyst for the reaction of an isocyanate group with a hydroxyl group, and curing the foam formulation to form a polyurethane foam.

2. The process of claim 1, wherein the one or more propylene oxide/ethylene oxide copolymers have a hydroxyl equivalent weight of at least 1000.

3. The process of claim 2 wherein the inner block of each of the two or more hydroxyl-terminated polyether chains of the one or more propylene oxide/ethylene oxide copolymers contain from 20 to 30% by weight oxypropylene units and from 70 to 80% by weight oxyethylene units and have a molecular weight of from 180 to 300.

4. The process of claim 3 wherein the outer block of each of the two or more hydroxyl-terminated polyether chains of the one or more propylene oxide/ethylene oxide copolymers contain from 0 to 2% by weight oxyethylene units.

5. The process of claim 4 wherein the one or more propylene oxide/ethylene oxide copolymers have a total oxyethylene content of from 12 to 18% by weight.

6. The process of claim 5 wherein the at least one blowing agent includes water.

7. The process of claim 6 wherein the sole blowing agent used in the process is water.

8. A polyurethane foam made by the process of claim 1.

Description

EXAMPLE 1 AND COMPARATIVE SAMPLES A AND B

(1) Glycerin is alkoxylated to a molecular weight of about 800 by polymerizing 12 moles of ethylene oxide and 3 moles of propylene oxide per mole of glycerin in the presence of a potassium hydroxide catalyst. This alkoxylation step is performed in a plug flow reactor having a volume of about 25 liters. This forms an intermediate having randomly polyether chains of approximately 234 molecular weight. These polyether chains contain approximately 75% by weight oxyethylene units and 25% by weight oxypropylene units. When the second step polymerization (described immediately below) is completed, these polyether chains will constitute the inner blocks of a propylene oxide/ethylene oxide copolymer of the invention.

(2) The intermediate is fed into a loop reactor that has a volume of 60 liters. Propylene glycol is fed into the reactor upstream of the point at which the intermediate is added, at a rate of about 1 mole of propylene glycol per 4.55 moles of the intermediate. Propylene oxide is fed into the reactor downstream of the point at which the intermediate is added. The loop reactor is operated at a flow rate of 7500 kg/hr, at a temperature of 160° C., and in the presence of 40 ppm of a zinc hexacyanocobaltate catalyst complex. Feed and product removal rates are selected to add poly(oxypropylene) blocks of about 962 onto the ends of the intermediate and onto the end of the propylene glycol. This produces a mixture of about 11% by weight of a poly(propylene oxide) diol having a molecular weight of about 2000, and about 89% by weight of a trifunctional propylene oxide/ethylene oxide copolymer that has a molecular weight of about 3600 (Polyol Example 1). The average molecular weight for the product is about 3300. The average functionality of the product is about 2.82. The propylene oxide/ethylene oxide copolymer has hydroxyl-terminated polyether chains extending from the residue of the glycerin molecules. The polyether chains include an inner block of about 234 molecular weight that contains about 75% by weight oxyethylene units and 25% by weight oxypropylene units. The polyether chains include an outer block of homopolymerized propylene oxide. The outer blocks have weights of approximately 962 molecular weight. The propylene oxide/ethylene oxide copolymer portion of Polyol Example 1 contains about 14.6% by weight oxyethylene units. Polyol Example 1 as a whole contains 13% by weight oxyethylene groups.

(3) Comparative Polyol A is prepared by alkoxylating glycerin with propylene oxide to form an intermediate having a molecular weight of about 800. The intermediate is fed into a loop reactor that has a volume of 60 liters. Propylene glycol is fed into the reactor upstream of the point at which the intermediate is added, at a rate of about 1 mole of propylene glycol per 4.55 moles of the intermediate. Propylene oxide and ethylene oxide are separately fed into the reactor downstream of the point at which the intermediate is added. The proportions of ethylene oxide and propylene oxide are selected so that the product (Comparative Polyol A) contains about 13% oxyethylene groups. The loop reactor is operated under the same conditions as described for Polyol Example 1, with feed and product removal rates again being selected to produce a product that has a molecular weight of 3300. Comparative Polyol A is a mixture of a difunctional, random copolymer of ethylene oxide and propylene oxide and a trifunctional polyol having inner all-propylene oxide blocks and outer blocks of randomly polymerized ethylene oxide and propylene oxide. This polyol is representative of randomly polymerized propylene oxide/ethylene oxide polyols that are commonly used to produce flexible slabstock polyurethane foams.

(4) Comparative Polyol B is prepared in the same manner as Polyol Example 1, except that the intermediate is made by homopolymerizing ethylene oxide onto glycerin, and the ratios of ethylene oxide and propylene oxide in the second polymerization step are adjusted to produce a polyol containing 13% oxyethylene groups. Comparative Polyol B generally represents the type of polyol described in CA 2,385,085, and is made to have the same average hydroxyl functionality and molecular weight as Polyol Example 1.

(5) Polyurethane foam Example 1 is prepared by processing Polyol Example 1 (100 parts), 0.05 parts of a tin catalyst, 0.15 parts of a tertiary amine catalyst, 0.7 parts of a silicone surfactant, 0.22 parts of stannous octoate (SO) and 2.2 parts water with an 80/20 mixture of the 2,4- and 2,6-isomers of toluene diisocyanate at a 110 index. Processing is performed on a Polymech slabstock foam machine using liquid laydown technology. Conveyor width is 80 cm; mixer speed is 6500 rpm, raw material temperatures are 23° C., and polyol output is 20 kg/minute. The foam is allowed to rise freely and cure.

(6) Comparative polyurethane foams A and B are prepared in like manner, substituting Comparative Polyols A and B, respectively, for the Polyol Example 1 material.

(7) Density, 40% compression force deflection, resilience, tear strength, tensile strength, elongation and 50%, 75% and 90% compression sets are measured. Results are indicated in the following table.

(8) TABLE-US-00001 Example or Comparative Sample Property Example 1 Comp. Sample A Comp. Sample B Density, kg/m.sup.3 41.0 39.3 40.7 40% Compression 3.80 3.86 3.70 Force Deflection, kPa Resilience, % 55.2 53.5 54.1 Tear strength, N/m 401 390 364 Tensile strength, kPa 100.8 87.4 88.1 Elongation, % 222 178 201 Compression Set, % 50% 0.25 0.36 0.19 75% 1.18 0.96 0.21 90% 1.58 2.77 2.17

(9) Polyurethane foam Example 1 has a 40% CFD value, resilience and compression set comparable to those of the Comparative Samples. However, tensile strength is about 10% greater than that of either of the Comparative Samples, even after adjusting for the slightly higher foam density of Example 1. This increase in tensile strength is achieved together with a small but significant increase in elongation. Tear strength is also increased relative to both Comparative Samples. In this set of tests, the polyol having an internal all-EO block (Comparative Polyol B) performs very similarly to Comparative Polyol A (the randomly polymerized material). Between those two polyols, the distribution of the oxyethylene units is not seen to have significant effect on the foam properties. However, when the ethylene oxide is distributed into an internal randomly polymerized block, terminated in an all-PO block (Polyol Example 1), a significant increase in tensile strength and elongation are seen, together with an increase in tear strength and without loss in other important properties.