Polyurethane Foams Made From Vinyl Polymer Polyols

This application is related to U.S. patent application Ser. No. 06/654,903, filed of even date, which is concerned with vinyl polymer polyols made using epoxy resin-modified polyols. The vinyl polymer polyols are used in the polyurethane foams of the instant invention.

1. Field of the Invention

This invention relates to polyurethane plastics more particularly relates to polyurethanes made using dispersions of polymers made from various vinyl monomers in the presence of polyols as the dispersing media.

2. Related Art in the Field

The use of a polyol in the preparation of polyurethanes by reaction of the polyol with a polyisocyanate in the presence of a catalyst and perhaps other ingredients is well known. Conventional polyols for flexible polyurethane foams are usually made by the reaction of a polyhydric alcohol with an alkyene oxide, usually ethylene oxide and/or propylene oxide, to a molecular weight of about 2,000 to 3,000 and above. These polyols are then reacted with polyisocyanate in the presence of water or other blowing agents such as fluorocarbons to obtain polyurethane foams. Polyols have been modified in many ways in attempts to improve the properties of the resulting polyurethane.

One common method of modifying polyols involves the use of polymers as the dispersed phase. One type is made by polymerizing vinyl monomers such as acrylonitrile and styrene in polyols. Another type includes the polymerization of vinyl monomers in polyol-isocyanate addition products. Another type involves the preparation of polyurea polymers by the reaction of diamines with diisocyanates in a polyol.

For example, U.S. Pat. No. 3,008,917 to Park, et al. teaches adding an unsaturated liquid monomer such as styrene to a polyester-isocyanate adduct which itself contains vinyl unsaturation. The resulting mixture is then copolymerized through the unsaturated linkages. U.S. Pat. No. 3,304,273 to Stamberger discloses a polymer polyol made by mixing a minor amount of a film-forming polymer having radicals reactive with the --N.dbd.C.dbd.O radicals of an organic polyisocyanate (such as polymers of acrylic acid, allyl alcohol, styrene, butadiene, etc.) in with a major amount of a solvent which also contains radicals reactive with an isocyanate group but has little or no ethylenic unsaturation (such as a polyol). Similar polymer polyols where the dispersed polymers consist of polymerized unsaturated monomers such as methacrylonitrile, styrene, etc., particularly copolymers using more than one kind of unsaturated monomer are disclosed in U.S. Pat. No. 3,383,351 to Stamberger. These materials are useful in preparation of polyurethane products.

U.S. Pat. No. 4,104,236 to Simroth reveals a liquid polymer polyol composition containing 45-90 wt. % of a polyoxypropylene polyol having a molecular weight of at least 1500 and 55 to 10 wt. % of a polymer. The polymer consists of 60 to 90 wt. % polymerized acrylonitrile and 40 to 10 wt. % of polymerized styrene. Polyurethane foams having high load-bearing properties and solid polyurethane elastomers having a high modulus were made from these materials. A polymer polyol consisting of 45 to 95 wt. % of a poly(oxypropyleneoxyethylene) polyol having a hydroxyl number of 20 to 60, an oxyethylene cap of 10 to 30 wt. % and an internal oxyethylene content of 5 to 60 wt. % and from 5 to 60 wt. % of a polymerized vinyl monomer (such as a co-polymer of styrene and acrylonitrile) is taught in U.S. Pat. No. 4,125,505 to Critchfield, et al. Further, U.S. Pat. No. 4,148,840 to Shah, et al. discloses polymer polyol compositions made by polymerizing one or more ethylenically unsaturated monomers in a polyol.

High resilience urethane foams may be prepared from tolylene diisocyanate and novel polymer polyol compositions made with acrylonitrile and vinylidene chloride monomers according to U.S. Pat. No. 4,214,055 to Seefried, et al. The acrylonitrile-vinylidene chloride polymer polyol compositions apparently enhance the load-bearing properties and decrease the flammability of the resultant foams. U.S. Pat. No. 4,226,756 to Critchfield, et al. teaches that polyol/vinyl polymer blends made by polymerizing acrylonitrile, styrene and/or methyl methacrylate in the presence of polyethylene-polypropylene glycols are useful in producing polyurethanes. Polymer stabilizers made by polymerizing 30:70 acrylonitrile-styrene mixtures with polypropylene glycol mono-butyl ether methacrylate are disclosed by U.S. Pat. No. 4,242,249 to Van Cleve, et al. as useful stabilizers for polyol-vinyl monomer reaction products.

U.S. Pat. No. 3,325,421 to Miller, et al. describes polyurea polymer polyols made by reaction of diamines with diisocyanate using a polyol as the dispersing media. See also British Pat. No. 899,413, which discloses the emulsion polymerization of vinyl monomers in a suspending agent where the agent is made by condensing polyethylene glycol with the diglycidyl ether of bisphenol A.

The polyols found to be useful as the dispersing media in this invention are polyols modified with epoxy resins. Generally, a polyepoxide is added into the reaction of a polyol initiator with mixtures of alkylene oxides before the alkylene oxide addition is complete. For example, see U.S. Pat. Nos. 4,316,991 and 4,373,034 both to Speranza, et al., incorporated by reference herein.

The invention concerns polyurethane foam made by reacting a vinyl polymer polyol together with an organic polyisocyanate in the presence of a polyurethane catalyst and optionally in the presence of a blowing agent. The vinyl polymer polyol is prepared by polymerizing via a free-radical reaction a vinyl monomer component having at least one vinyl monomer in the presence of an epoxy-resin modified polyol having a molecular weight of 2,000 to 7,000.

Polymer polyols are typically prepared by the free-radical catalyzed polymerization of vinyl monomers by using various polyols as the dispersing media. These polymer polyols have been used to enhance the load-bearing properties of molded high resilience foam used in automotive seating and slab flexible foam used in carpet underlay.

It has been discovered that the preparation of vinyl polymer polyols by the free radical-initiated polymerization of vinyl monomers in epoxy resin-modified polyols as the reaction media gives polymer polyols which are more effective than conventional polymer polyols in increasing the load-bearing properties of polyurethane flexible foams. In addition, firmer polyurethane foams using polymer polyols with lower polymer loadings can be produced using the polymer polyols of the invention.

The monomers employed in preparing the vinyl polymer polyols useful in this invention are the polymerizable monomers characterized by the presence therein of at least one polymerizable ethylenic unsaturated group of the type C.dbd.C. The monomers can be used singly or in combination to produce homopolymer/reactive solvent products or copolymer/reactive solvent combinations, respectively.

Preferably, the monomers contain the double bond in a vinyl group. These monomers are well known in the art and include the hydrocarbon monomers such as styrene, butadiene, isoprene, 1,4-pentadiene, 1,6-hexadiene, 1,7-octadiene, .alpha.-methylstyrene, methyl styrene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, and the like; substituted styrenes such as chlorostyrene, 2,5-dichlorostyrene, bromostyrene, fluorostyrene, trifluoromethyl styrene, iodostyrene, cyanostyrene, nitrostyrene, N,N-dimethylaminostyrene, acetoxystyrene, methyl 4-vinylbenzoate, phenoxystyrene p-vinyldiphenyl sulfide, p-vinylphenyl oxide, and the like. Also suitable are acrylic and substituted acrylic monomers such as acrylic acid, methacrylic acid, acrylonitrile, methyl methacrylate, methyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, cyclohexylmethacrylate, benzyl methacrylate, isopropyl methacrylate, octyl methacrylate, methacrylonitrile, methyl alphachloroacrylate, ethyl alpha-ethoxy acrylate, methyl alphaacetaminoacrylate, butyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, phenyl methacrylate, .alpha.-chloroacrylonitrile, N,N-dimethylacrylamide, N,N-dibenzylacrylamide, N-butylacrylamide, methacrylyl formamide, and the like. The vinyl esters, vinyl ethers, vinyl ketones, etc. are also useful, such as vinyl acetate, vinyl chloroacetate, vinyl alcohol, vinyl butyrate, isopropenyl acetate, vinyl formate, vinyl acrylate, vinyl methacrylate, vinyl methoxy acetate, vinyl benzoate, vinyl iodide, vinyl toluene, vinyl naphthalene, vinyl bromide, vinyl fluoride, vinyldiene bromide, 1-chloro-1-fluoroethylene, vinyldiene fluoride, vinyl methyl ether, vinyl ethyl ether, vinyl propyl ethers, vinyl butyl ethers, vinyl 2-ethylhexyl ether, vinyl phenyl ether, vinyl 2-methoxyethyl ether, methoxybutadiene, vinyl 2-butoxyethyl ether, 3,4-dihydro-1,2-pyran,2-butoxy-2'-vinyloxy diethyl ether, vinyl 2-ethylmercaptoethyl ether, vinyl methyl ketone, vinyl ethyl ketone, vinyl phenyl ketone, vinyl ethyl sulfide, vinyl ethyl sulfone, N-methyl-N-vinyacetamide, N-vinylpyrrolidone, vinyl imidazole, divinyl sulfide, divinyl sulfone, sodium vinyl sulfoxide, methyl vinyl sulfonate, N-vinyl pyrrole and the like. Other compounds expected to be useful are dimethyl fumarate, dimethyl maleate, maleic acid, crotonic acid, fumaric acid, itaconic acid, monomethyl itaconate, t-butyl aminoethyl methacrylate, dimethylaminoethyl methacrylate, glycidyl acrylate, allyl alcohol, glycol monoesters of itaconic acid, dichlorobutadiene, vinyl pyridine, and the like. Any of the known polymerizable monomers can be used and the compounds listed above are illustrative and not restrictive of the monomers suitable for use in this invention.

Vinyl monomers are preferred, and styrene, acrylonitrile, methyl methacrylate, methyl acrylate and butadiene are particularly preferred. It is especially preferred that styrene and acrylonitrile be used together. The preferred mole ratio of styrene to acrylonitrile ranges from 9:1 to 1:9. Any of the known chain transfer agents can be present, if desired.

Polymerizing the monomers in the epoxy resin-modified polyol solvent occurs in the presence of a catalytically effective amount, preferably 0.5 to 5.0 wt. % based on total feed, of a conventional free radical catalyst known to be suitable for the polymerization of ethylenically unsaturated monomers. Preferred catalysts are the azo-bis compounds such as alpha, alpha'-azo-2-methyl butyronitrile, alpha, alpha'-2-methyl heptonitrile, 1,1'-azo-isobutyrate, 4,4'-azo-4-cyanopentanoic acid, azobisisobutyronitrile and the like. Other preferred catalysts are organic peroxides, peroxydicarbonates and peroxyesters. Illustrative catalysts are the well-known free radical type of vinyl polymerization catalysts, for example, the peroxides, persulfates, perborates, percarbonates, azo compounds, etc., including hydrogen peroxide, dibenzoyl peroxide, acetyl peroxide, benzoyl hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, butyryl peroxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, diacetyl peroxide, di-alpha-cumyl peroxide, dipropyl peroxide, diisopropyl peroxide, isopropyl-t-butyl peroxide, butyl-t-butyl peroxide, dilauroyl peroxide, difuroyl peroxide, ditriphenylmethyl peroxide, bis(p-methyoxybenzoyl) peroxide, p-monomethoxybenzoyl peroxide, rubrene peroxide, ascaridole, t-butyl peroxybenzoate, diethyl peroxyterephthalate, propyl hydroperoxide, isopropyl hydroperoxide, n-butyl hydroperoxide, t-butyl hydroperoxide, cyclohexyl hydroperoxide, trans-decalin hydroperoxide, alpha-methylbenzyl hydroperoxide, alpha-methyl-alpha-ethyl benzyl hydroperoxide, tetralin hydroperoxide, triphenylmethyl hydroperoxide, diphenylmethyl hydroperoxide, persuccinic acid, diisopropyl peroxy dicarbonate, and the like. A mixture of catalysts may also be used.

Especially preferred are polymerization catalysts manufactured by the E. I. duPont de Nemours and Co. such as 2,2'-azobis(2,4-dimethylpentanenitrile), 2,2'-azobis(2-methylpropanenitrile), 2,2'-azobis(2-methylbutanenitrile), and 1,1'-azobis(cyanocyclohexane). These products are commercially sold as VAZO.RTM. 52, 64, 67, and 88, respectively.

The polymerization must occur in an epoxy resin-modified polyol as the dispersing media. Preferably, these modified polyols are made by the reaction of a polyol initiator having an active hydrogen functionality of 3 to 8 with one or more alkylene oxides and an epoxy resin in such a manner that the epoxy resin is added internally along the length of the polyol chain. This result may be obtained, for instance, with a three-step procedure: (1) reacting a polyol initiator with an alkylene oxide, (2) reacting the alkoxylated initiator with an epoxy resin, and (3) reacting the product from step 2 with additional alkylene oxide. The final polyol preferably has a molecular weight in the range of about 2,000 to 7,000.

Suitable polyol initiators include, for example, glycerine, trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol, triethanolamine, ethylenediamine, aminoethylpiperazine, sorbitol, and sucrose, or mixtures thereof. These are only mentioned for purposes of illustration. It is even expected that dihydric initiators may prove to be useful as polyol initiators in this role. For example, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and other diols are expected to be useful under the proper conditions. The alkylene oxides useful in making the modified polyols of this invention are preferably ethylene oxide, propylene oxide and 1,2-butylene oxide. Ethylene oxide and propylene oxide are preferred. More than one oxide may be added to the modified polyol intermediates as deemed necessary by one skilled in the art. The reactions involving the opening of various terminal epoxide groups are catalyzed usually with a basic compound. For instance, common alkaline catalysts normally employed are sodium hydroxide and potassium hydroxide.

It is anticipated that a wide variety of epoxy resins would be useful in making the epoxy resin-modified polyols suitable for the polymer polyols. The vicinal polyepoxide-containing compounds are organic materials having an average of at least 1.8 reactive 1,2-epoxy groups per molecule. The polyepoxide materials can be monomeric or polymeric, saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and may be substituted, if desired, with other substituents besides epoxy groups, e.g., hydroxyl groups, ether radicals, aromatic groups, halogen atoms or the like. Preferably, the epoxy resin is the diglycidyl ether of bisphenol A.

The epoxy resin-modified polyols used in this invention may be made at conditions of temperature and pressure selected to give a polyol having certain characteristics. Typical conditions are a pressure of around 50 psig and a temperature of about 50.degree. to 150.degree. C. The amount of epoxy resin to be added to the reaction mixture should be such that the epoxy equivalents present are less than half of the hydroxyl functionality equivalents present in the reaction mixture. Too many epoxy equivalents in relation to the hydroxyl equivalents may cause the epoxy resin to gel by cross-linking with itself. Other details about the preparation of the epoxy resin-modified polyols useful in this invention may be found in U.S. Pat. No. 4,316,991 which is incorporated herein by reference.

To obtain the vinyl polymer polyols of this invention, the epoxy resin-modified polyol is preferably added first to the reaction vessel. It is usually best that the polyol be heated to the reaction temperature before the next step, which is the slow or dropwise addition of a mixture of the vinyl monomer component (which may be more than one kind of vinyl monomer) and the free radical initiator. After the reaction proceeds for a short time (0.25 to 1.0 hour), volatiles are stripped off by conventional techniques to leave the vinyl polymer polyol product.

The reaction temperature should be about 75.degree. to 150.degree. C., preferably 90.degree. to 140.degree. C. Reaction pressures may range from atmospheric pressure to about 100 psig. When mixed vinyl monomers are used, such as styrene and acrylonitrile, the mole ratios should range from about 9:1 to 1:9 or preferably 30:70 to 70:30. The amount of polymer in the polyol, also known as "polymer loading" may range from 5 to about 40 wt. %, preferably from about 10 to 40 wt. %. The vinyl polymer polyols of this invention surprisingly give improved polyurethane foams with improved load-bearing properties even at relatively low polymer loadings.

It has been discovered that polyurethane foams may be made by reacting the vinyl polymer polyols described above with an organic polyisocyanate in the presence of a polyurethane formation catalyst. A blowng agent such as a halocarbon (trichlorofluoromethane, for example), water or carbon dioxide may also be present. The polyurethane formation catalysts are typically tin catalysts or tertiary amine compounds. Other additives such as silicone surfactants, etc. may also be present. For more information on preparing polyurethanes, particularly flexible polyurethanes, see U.S. Pat. Nos. 4,338,408; 4,342,687 and 4,381,353, incorporated herein by reference. Surprisingly, the foams made using the vinyl polymer polyols described herein have improved load bearing properties. Flexible carpet underlay foam and molded automobile foam with lower polymer loadings and better load bearing properties may be prepared using the techniques mentioned herein. These improvements are accomplished with lower levels of polymer polyol, which is a significant advantage in foam manufacture.

The preparation of the vinyl polymer polyols will be further illustrated by the following examples, which are not intended to limit the invention. The use of the vinyl polymer polyols of this invention in flexible polyurethane foams will also be demonstrated. The advantages over foams made from conventional polyols, conventional epoxy resin-modified polyols and conventional polymer polyols will also be shown.

Four hundred grams of a 5,000 molecular weight epoxy resin-modified glycerine-based triol were charged into a one-liter three-necked flask equipped with a stirrer, thermometer, dropping funnel, water condenser, and nitrogen source. The polyol was prepared as described in U.S. Pat. No. 4,316,991. It had a hydroxyl number of 33.6 mg KOH/g, contained 0.5 wt. % combined diglycidyl ether of bisphenol A (DGEBPA), and had been capped with 12 wt. % ethylene oxide (EO) to contain 76% primary hydroxyl groups.

Maintaining a nitrogen purge, the polyol was heated to 130.degree. C. A mixture of 60 g acrylonitrile, 40 g styrene and 5 g 2,2'-azobis(2-methylbutyronitrile)* was added dropwise over a 40-minute period, maintaing the reaction temperature at 128.degree.-130.degree. C. The reaction mixture was then digested 15 minutes and vacuum stripped to 5 mm Hg. The recovered volatiles (5.6 g) corresponded to a monomer conversion of 94.4%. The finished product was an off-white viscous dispersion which had the following properties:

Acid no., mg KOH/g: 0.013

Hydroxyl no., mg KOH/g: 27.8

Water, wt. %: 0.02

Viscosity, 77.degree. F., cps: 2592

Appearance: Homogeneous dispersion

These examples will illustrate the preparation of polymer polyols using a 3,500 molecular weight epoxy resin-modified polyol as the dispersing media. This polyol is marketed by Texaco Chemical Co. as THANOL.RTM. F-3550 polyol, which is made according to the U.S. Pat. No. 4,316,991 procedures. The general procedure of Example 1 was used in these experiments. Reaction charges, details of preparation and properties are as follows:

These examples will illustrate the preparation of polymer polyols using a 3,000 molecular weight epoxy resin-modified triol (THANOL.RTM. F-3050 made by Texaco Chemical Co.) as the dispersing media. The general procedure of Example 1 was used in these experiments. Reaction charges, details of preparation, and properties are as follows:

This example will show the preparation of a polymer polyol using a 45.4 hydroxyl number sucrose/glycerine initiated, DGEBPA-modified polyol in the dispersing media. This polyol had a propylene oxide/ethylene oxide ratio of 80.8:19.2 and contained 0.5 wt. % combined DGEBPA. The general procedure of Example 1 was used for preparation of this polymer polyol. Reaction charges, details of preparation and properties are shown in the following table:

This example will shown the use of the polymer polyols of this invention in the preparation of the flexible polyurethane foam of this invention. It will further show the improved load bearing properties (as measured with a Chatillon gauge) of these foams as compared to those made from prior art polyols. In these formulations, the tin level was adjusted to make all foams with the same degree of openess.

Formulations and foam properties are shown in the following table:

It may be seen from Example 7 that foams made from the vinyl polymer polyols of this invention (Foams, D, E, F, and G) have better load bearing properties (Chatillon gauge readings of 4.64-4.94) than a foam made from a conventional polyol (Foam A, 4.31 reading) or foams made from conventional epoxy resin-modified polyols (Foams B and C, 4.55 and 4.48 readings, respectively). The Chatillon gauge measures the number of pounds it takes to indent a standard piece of foam 25% in height.

This example will show that polymer polyols of this invention are more effective at raising the hardness of flexible foams than prior art polymer polyols. In these formulations, the tin catalyst level was adjusted to prepare all foams with the same degree of openness.

Formulations and foam properties are shown in the following table.

From Example 8, it is discovered that foams made from the vinyl polymer polyols of this invention (Foams H and I) have greater load-bearing strength (Chatillon readings of 4.98 and 4.94, respectively) than a foam made using a conventional polymer polyol (Foam J, with a reading of 4.86).

Many modifications may be made in the polyurethane foams of this invention without departing from the spirit and scope thereof which are defined only in the appended claims. For example, one skilled in the art may find that using a particular combination of vinyl monomers and epoxy resin-modified polyols, proportions thereof and certain reaction conditions give a polymer polyol which produces a polyurethane with especially advantageous properties.