Use of Liquid Oxazolines in Polyurethane/Polyisocyanurate Rigid Foams as Reactive Compatibilizers

This invention relates to the use of liquid oxazolines as reactive compatibilizers in the formation of certain polyurethane/polyisocyanurate rigid foams and more particularly pertains to the use of liquid oxazolines to improve the compatibility between fluorocarbon blowing agents and polyols in the formation of polyurethane/polyisocyanurate rigid foam.

U.S. Pat. No. 4,237,238 describes improved polyisocyanurate foams of high degree of fire resistance with low smoke evolution on combustion and low friability obtained by the reaction of polyisocyanates and a terephthalic ester polyol in the presence of a blowing agent. Such polyols obtained by the transesterification of a residue of dimethylterephthalate with a glycol of molecular weight 60 to 400 are more completely described in U.S. Pat. No. 3,647,759. Although the foams have some good properties, unfortunately, the polyols used in U.S. Pat. No. 4,237,238 have poor compatibility with the fluorocarbon blowing agent. U.S. Pat. No. 4,339,343 discloses miscible blends of 20-85% alkoxylated alkyl amines with 15-80% primary hydroxyl polyols and fluorocarbon blowing agent. The use of amide diols of the type described in U.S. Pat. No. 4,246,364 as compatibilizing agents has been disclosed in U.S. Pat. No. 4,444,916.

I have now found that the addition of small amounts of liquid oxazolines having the Formula I (below) to certain polyols used in the formation of polyurethane/polyisocyanurate rigid foams wherein a fluorocarbon blowing agent is used leads to significant improvement in the compatibility of the fluorocarbon and polyol which in turn leads to a rigid foam which is of a uniform cellular structure throughout. ##STR1## wherein R, R', R"' and R"" independently represent hydrogen, an alkyl group having from 1 to 10 carbon atoms or a hydroxy alkyl group having from 1 to 10 carbon atoms and R" represents hydrogen, an alkyl group having from 1 to 19 carbon atoms, an aryl group having from 6 to 12 carbon atoms or a hydroxy alkyl group having from 1 to 19 carbon atoms.

The fluorocarbon blowing agent used in this invention is normally used in amounts between about 5 and about 50% by weight, preferably between about 10 and about 35% by weight based on polyisocyanate with the amount used depending largely upon the desired foam density. The amount used will effect foam density and closed cell content of the foam. This will usually result in blowing agent being present in the reaction mixture of the invention in amounts between about 15 and about 175% by weight based on the total polyol. Trichlorofluoromethane is preferred as the blowing agent. Other suitable blowing agents include, for instance, dichlorodifluoromethane, 1,1-dichloro-1-fluoroethane, hexafluorocyclobutene and octafluorocyclobutane.

The polyisocyanates useful in this invention include organic isocyanates having at least two isocyanate groups per molecule. The polyisocyanates can be of low, high or intermediate molecular weight and can be any of a wide variety of organic polyisocyanates including ethylene diisocyanate, trimethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, hexamethylene diisocyanate trimer, tetraethylene diisocyanate, pentamethylene diisocyanate, propylene-1,2-diisocyanate, 2,3-dimethyl tetramethylene diisocyanate, butylene-1,2-diisocyanate, butylene-1,3-diisocyanate, 1,4-diisocyanato cyclohexane, cyclopentene-1,3-diisocyanate, p-phenylene diisocyanate, 1-methyl phenylene-2,4-diisocyanate, naphthalene-1,4-diisocyanate, toluene diisocyanate, diphenyl-4,4'-diisocyanate, benzene-1,2,4-triisocyanate, xylene-1,4-diisocyanate, xylylene-1,3-diisocyanate, 4,4'-diphenylene methane diisocyanate, 4,4'-diphenylene propane diisocyanate, 1,2,3,4-tetraisocyanato butane, butane-1,2,3-triisocyanate, polymethylene polyphenyl isocyanate, and other polyisocyanates having an isocyanate functionality of at least two more fully disclosed in U.S. Pat. Nos. 3,350,362 and 3,382,215. Polyisocyanates which are polymeric in nature including isocyanate prepolymers of all types are included in this invention.

Isocyanate trimerization catalysts are preferably included in the mixtures of this invention prior to foaming of same. The isocyanate trimerization catalysts employed in this invention can be any catalyst known to those skilled in the art which will catalyze the trimerization of an organic isocyanate compound to form the isocyanurate moiety. Trimerization catalyst is usually used in amounts between about 0.1 and about 5% by weight based on the weight of the polyisocyanate. Most commonly used trimerization catalysts also function to catalyze the reaction of polyol and isocyanate to form urethane. The use of such dual function catalysts is preferred, but a separate catalyst may if desired be used for urethane formation. If used, urethane catalyst is normally used in amounts between about 0.05 and 3% by weight based on polyisocyanate. Suitable dual function catalysts include, for instance, one or more metal carboxylates such as potassium acetate, potassium octoate, sodium octoate or calcium octoate. Mixtures of such carboxylates with tertiary amines are also suitable as are N-hydroxyalkyl quaternary ammonium carboxylates. Suitable urethane catalysts include, for instance, tertiary amines such as triethyl amine or dimethyl ethanol amine as well as 1.4-diazadicyclooctane (2,2,2) and organo tin compounds such as dibutyl tin diacetate, stannous octoate and dibutyltin dilaurate.

Polyols useful in this invention comprise at least about 60% of the polyol mixture of a material prepared by the transesterification with a glycol of molecular weight from about 60 to about 400 of residue remaining after dimethyl terephthalate and methyl p-toluate have been removed from dimethyl terephthalate esterified oxidate reaction product, the major portion of said residue comprising a mixture of methyl and benzyl esters of benzene and biphenyl di- and tricarboxylic acids. The polyol is used in foams of the invention in amounts between about 0.1 and about 1.0 hydroxyl equivalent of total polyol per equivalent of polyisocyanate. Use of between about 0.15 and about 0.5 hydroxyl equivalent of polyol on the same basis is frequently preferred. Polyol used in forming reaction mixture and foam of the invention comprises at least about 60% by weight, preferably at least about 75% by weight and still more preferably at least about 95% by weight of polyol mixture prepared by transesterification with a glycol of molecular weight from about 60 to about 400 of a residue remaining after dimethyl terephthalate and methyl p-toluate have been removed from a dimethyl terephthalate esterified oxidate reaction product, the major portion of said residue comprising a mixture of methyl and benzyl esters of benzene and biphenyl di- and tricarboxylic acids. Such polyol mixtures are described in detail in U.S. Pat. No. 4,237,238 the disclosure of which is incorporated herein by reference.

The transesterified polyol mixture may be prepared by heating the residue defined above with the transesterifying glycol in accordance with the procedures described in U.S. Pat. No. 3,647,759 the disclosure of which is also incorporated herein by reference.

The transesterifying step is simply the replacement of the non-hydroxyl containing carbomethoxy groups in the various aromatic esters of the residue by the glycol agents so that the ester groups now contain, for the most part, terminal hydroxyl groups. Illustrative of the esterifying glycols which can be employed are ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,2-hexanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, tripropylene glycol, polyoxyethylene glycols, and polypropylene glycols. A preferred group of glycols consists of ethylene glycol and diethylene glycol with the latter being most preferred.

Examples of ethylene glycol and diethylene glycol transesterified residues which are used in accordance with the present invention are those produced commercially under the tradename of Terate resins and supplied by Hercules, Inc., Wilmington, Delaware and Chardol resins supplied by Chardonol Corporation. Polyol viscosity sometimes requires adjustment or modification in order to balance component pumping ratios or to satisfy some other processing requirement. Although the polyol mixtures can be readily produced as fluid materials, particularly by employing excess glycol transesterifying agent and leaving residual glycol in the resin, it is also feasible to employ additional diluents with the polyol mixtures.

As mentioned earlier, the polyol mixtures described above must comprise at least about 60% by weight and preferably at least about 75% by weight of the total polyol content of reaction mixtures and foams of the invention. The remaining polyol content, if any, of reaction mixtures and foams of this invention may be any polyol of the types conventially used in making rigid polyurethane and polyisocyanurate foams. Suitable polyols include those mentioned in U.S. Pat. No. 4,094,869 the disclosure of which is incorporated herein by reference. The other polyols useful in this invention include those having at least two hydroxyl groups per molecule and having equivalent weights falling in the range of from 20 to 5000. Specific polyols include butane diol, cyclohexane dimethanol, tripropylene glycol, amide diols, urethane diols, polyether polyols such as poly(tetramethylene ether) diols, poly(propylene ether) polyols, polyester polyols, and the like.

Polyhydroxy polyethers are suitable and preferably those having at least 2 hydroxyl groups per molecule. Polyhydroxy polyethers can be prepared by polymerization of epoxides such as ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide, or epichlorohydrin either on their own or by chemical addition to other materials. Suitable other materials include ethylene glycol, propylene glycol, trimethylol propanes and 4,4'-dihydroxy diphenyl propane. Sucrose polyethers also may be used. Polybutadienes having hydroxyl groups as well as other known hydroxyl containing vinyl polymers can be used. Hydroxyl containing polyesters, polythioethers, polyacetals, polycarbonates or polyesteramides of the types known for the formation of polyurethanes may also be used.

Foaming agents and other optional additives such as dispersing agents, cell stabilizers, surfactants, flame retardants, and the like, can be employed according to the teachings of the patents referred to above. Use of flame retardants tends to even further improve compatibility of the polyols and blowing agents used in accordance with the invention. In this respect suitable flame retardants include tris(dichloropropylphosphate) which is a preferred flame retardant for use in this invention.

A conventional surfactant, such as a silicone surfactant is preferably incorporated in the reaction system of the invention in amounts between about 0.5 and about 3% by weight based on isocyanate. Illustrative of these are the polyoxalkylenepolydimethyl siloxane block copolymers. Other nonionic, cationic, and anionic surface active agents may also be used.

The proportion of isocyanate groups to hydroxyl groups in the reactant polyols described above (and thus including the total polyols) is desirably from 1 to 10 and preferably 4 to 7, respectively. The amount of oxazoline in the polyol mixtures can be in the range of from 1 to 50% by weight and preferably from 5 to 30%. The oxazoline functionality is at least bi-functional with respect to isocyanate. Thus, the overall portion of isocyanate groups to combined hydroxyl and oxazoline groups is preferably from 1 to 10 and preferably from 3 to 7, respectively.

Reaction mixture of the invention may be formed by mixing the required ingredients of the foam (except for the polyisocyanate) in any suitable manner such as by introducing all of the ingredients into a suitable container or receptical and stirring or blending to obtain a relatively stable, homogeneous mixture. The ingredients may be introduced sequentially or simultaneously. Polyisocyanate is then added to initiate the reactions necessary to make rigid foams of the invention. Reaction mixture of the invention may, for instance, be combined with polyisocyanate immediately prior to or simultaneously with the dispensing of the mixture onto a moving conveyor belt to foam the mixture to form rigid foam which may be post cured, all in a conventional manner. Post curing is generally carried out in the absence of moisture at ambient or, if desired to accelerate the cure, at elevated temperatures, the permissible range being desirably about 20 degrees to 100 degrees C. for periods of time which will vary inversely with the curing temperature employed and varying from about a few minutes to about 48 hours. This post cure serves to complete the formation substantially of trimer within the foam structure.

Because of the improved compatibility between ingredients due to the presence of the liquid oxazoline, the reaction mixture of this invention has greatly improved stability. Depending upon such factors as storage temperature, amount of agitation during storage, presence of surfactant or flame retardant and amounts and types of polyols and oxazoline used, reaction mixtures of the invention will remain homogeneous with no noticeable separation of blowing agent for periods of time ranging from a few minutes to almost indefinitely. In many instances the reaction mixture of the invention will remain stable and homogeneous for at least about 20 minutes. This allows the mixtures to be completely formed and then stored for at least a short time before use. By contrast, in reaction mixtures of this general type taught by the prior art, e.g., U.S. Pat. No. 4,237,238, the fluorocarbon blowing agent begins to separate almost immediately so that uneven foam results if the mixture is not used immediately. The use of well known fillers such as talc, alumina, silica, glass beads, etc. in the materials of this invention is within the scope of this invention.

The following representative examples will further illustrate the invention.

This Example which is outside the scope of the present invention demonstrates the poor compatibility of the polyol with the fluorocarbon blowing agent when the oxazoline compatibilizing agent is not included in the mixture. In a 25 ml jar were placed 10.3 g of commercially available poly(terephthalic ester) polyol (Chardol 570, hydroxyl no. about 350) and 4.3 g of Freon (F-11B) (which is trichlorofluoro methane) and the mixture was blended vigorously and then kept undisturbed at room temperature. A phase separation was observed within 5 minutes.

The polyol of Example 1 (10.12 g) was mixed with 3.02 g of oxazoline of Formula I in which R and R' represent methyl, R"' and R"" represent hydrogen and R" represents a butylene hydroxyl group to give a solution. To this solution was added 5.0 g of Freon F-11B and the mixture was blended vigorously. The resulting mixture was stored undisturbed at room temperature and no phase separation was observed even after 5 hours standing.

The procedure of Example 2 was followed using 10.12 g of Chardol polyol, 3.14 g of the oxazoline and 6.37 g of Freon F-11B. No phase separation was observed after 5 hours standing.

The procedure of Example 2 was followed using 10.19 g of Chardol polyol, 2.08 g of oxazoline and 4.55 g of Freon F-11B. No phase separation occurred within one hour.

The procedure of Example 2 was followed using 10.06 g of Chardol polyol, 1.16 g of the oxazoline and 4.16 g of Freon F-11B. No phase separation was observed after 20 minutes standing.

This Example which is outside the scope of the present invention demonstrates the preparation of a rigid foam without the use of an oxazoline compatibilizing agent. A poly(terephthalic ester) polyol (Chardol 570 polyol) (12.14 g), 0.2 g of low viscosity silicone-glycol surfactant (DC-193 from Don Corning), 0.2 g of tertiary amine catalyst (Polycat 41, which is tris(dimethylamine propyl)-hexahydrotriazine)) and 4.5 g of Freon F-11B were vigorously mixed in a paper cup and to this mixture was added 12.4 g of polymeric MDI (modified 4,4'-methylene bis (phenyl isocyanate)). This material was mixed for 10 seconds and kept at room temperature for forming the foam. The foam was observed to have a cream time of 20 seconds, rise time of 40 seconds, tack-free time (gel time) of 46 seconds and the final foam was found to be of irregular composition with some unfoamed polymer at the bottom of the cup. The more uniform part of the foam (upper portion) was found to have a density of 2.3 pounds/cubic foot and a compressive strength of 20 psi.

The procedure of Example 6 was followed using 10.02 g of Chardol polyol, 2.0 g of the oxazoline described in Example 2, 0.3 g of silicone surfactant (DC-193) and 5 g of Freon F-11B. The mixed solution was further mixed with 18.2 g of the polyisocyanate. No catalyst was used. The foaming characteristics were a cream time of 50 seconds, rise time of 100 seconds, tack free time of 110 seconds and after being post cured at 95 degrees C. for 5 minutes the resulting homogeneous rigid foam was found to have a uniform density of 2.0 pounds/cubic foot, a compressive strength of 18 psi and low surface friability.

The procedure of Example 6 was followed using 10.02 g of Chardol polyol, 3.,03 g of an oxazoline of Formula I in which R is ethyl, R' is methylene hydroxy, R"' and R"" are hydrogen, and R" is butylene hydroxy, 4.15 g of Freon F-11B and 0.3 g of tertiary amine catalyst (Polycat 41). The foaming characteristics were cream time of 20 seconds, rise time of 35 seconds, tack free time of 42 seconds and the resulting rigid foam was found to be uniform having a density of 1.4 pounds/cubic foot and a compressive strength of 12 psi.

The procedure of Example 1 was followed using 10.02 g of Chardol polyol, 3.03 g of the oxazoline described in Example 8 and 4.15 g of Freon F-11B. The mixed solution remained homogeneous for one hour at room temperature undisturbed.

The procedure of Example 1 was followed using 10.2 g of terephthalic ester polyol (Terate 203 by Hercules, Inc., hydroxy No. 323), 1.05 g of the oxazoline described in Example 8 and 4.08 g of Freon F-11B. No phase separation was observed after 30 minutes of standing undisturbed at room temperature.

The procedure of Example 1 was followed using 10.1 g of Terate 203, 1 g of the oxazoline of Formula I in which R, R', R"' and R"" are hydrogen and R" is methyl, and 4.5 g of Freon F-11B. The homogenized mixture did not separate after 30 minutes standing undisturbed at room temperature.