USE OF CERTAIN CATALYST COMPOSITIONS FOR THE PREPARATION OF POLYURETHANES

Abstract: A catalyst composition for polyurethane production by reaction between aliphatic hydroxyl-containing compounds and secondary and or tertiary aliphatic isocyanate com­ pounds, comprising (a) lead naphthenate and (b) a dialkyl tin dicarboxylate compound in a weight ratio of from about 25:75 to about 75:25.

Description: IMPROVED POLYURETHANE CATALYST COMPOSITIONS The present invention generally relates to preparation of polyurethanes from hindered aliphatic isocyanates, and particularly to improvements in catalysis of the reaction between hindered aliphatic isocyanates and hydroxyl-containing compounds. More specifically, the invention relates to novel synergistic catalyst compositions for the formation of polyurethane by reaction between hydroxyl-containing compounds and secondary and/or tertiary aliphatic diisocyanates. The term "aliphatic isocyanate" refers to compounds in which the isocyanate group (-NCO) is attached to a carbon atom not in an aromatic ring, and hindered isocyanates are those in which the carbon atom to which the isocyanate group is attached is provided with at least one other inert substituent, generally a lower (C1-Cg) alkyl group. The preparation of polyurethanes from aliphatic isocyanates is well-known and the advantages derived therefrom are appreciated by those skilled in the art. Primary aliphatic isocyanates, for example,1,6-hexamethylene diisocyanate, react significantly faster with compounds containing amino, carboxyl and hydroxyl groups than secondary or tertiary isocyanates. However, many isocyanates containing secondary and/or tertiary isocyanate groups are known and some of them provide highly useful polyurethane products. Unfortunately, they usually are exceedingly slow reacting and require catalysis, especially in reactions with hydroxyl-containing compounds. Reaction injection molding, commonly referred to by the acronym RIM, is a relatively recent advance in polyurethane technology. The process requires fast polyurethane reactions, that is, on the order of seconds at temperatures in the range of about 25-400C. Commonly used polyurethane catalysts, such as lead naphthenate and dialkyl tin dicarboxylates, are not adequate to promote the reaction between hindered aliphatic isocyanates and hydroxyl-containing compounds under these conditions. It is, therefore, a principal object of the present invention to provide catalyst compositions which increase the rate of reaction between hindered aliphatic secondary and/or tertiary isocyanates and hydroxyl-containing compounds. It is another object of the invention to provide catalyst compositions for the practical utilization of hindered aliphatic secondary and/or tertiary isocyanates in the RIM reaction with hydroxyl-containing compounds. It is still another object of the invention to provide catalyst compositions for the RIM reaction between aliphatic tertiary diisocyanates and both primary and secondary polyols. In accordance with the present invention, it has been discovered that certain combinations, or mixtures, of lead naphthenate and dialkyl tin dicarboxylates provide enhanced reaction rates between hindered aliphatic secondary and/or tertiary isocyanates and hydroxyl-containing compounds. More specifically, certain combinations of lead naphthenate and dialkyl tin dicarboxylates are synergistic and provide rates of reaction several times faster than are obtained with either catalyst component alone. The catalyst compositions of the present invention are effective in accelerating the reaction between hydroxylcontaining compounds and aliphatic isocyanates containing at least one secondary or tertiary isocyanate group. Stallmann, U.S. Patent 2,723,265, describes the preparation of a broad range of hindered isocyanates represented by the formula: EMI3.1 wherein R1 and R2 represent lower alkyl (C1-Cg) groups and X represents a bridging unit. A process for the preparation of compounds containing secondary and tertiary isocyanates is disclosed by Hoover, U.S. Patent 3,290,350. In the process disclosed in this patent, isocyanic acid is added to a compound containing at least one reactive vinylidene group, of the formula: EMI3.2 wherein R1 is selected from the group consisting of hydrogen and hydrocarbyl (Cl-Cl2) groups and R2 is hydrogen, hydrocarbyl (C1-C12) or substituted hydrocarbyl, wherein thesubstituents are inert to isocyanic acid and are bonded to a carbon atom at least 2 carbon atoms removed from the ethylenic linkage, or R1 and R2 are conjointly hydrocarbylene of 2-12 carbon atOms. Isocyanates prepared according to this process contain the group: EMI3.3 A particularly useful clas-s of isocyanates prepared according to the process of the Hoover patent are those derived from compounds having more than one vinylidene group, the product isocyanates being represented by the formula: EMI4.1 <tb> <SEP> R1 <SEP> R1 <tb> OCN-C--arylene--C--NCO <tb> <SEP> R2 <SEP> R2 <tb> wherein R1 is hydrogen or C1-C4 alkyl and R2 is hydrogen or C1-C4 alkyl. A wide range of botb secondary and/or tertiary isocyanates and diisocyanates may be prepared in accordance with the aforementioned prior art, the reaction of which with hydroxyl-containing compounds may ugefully be catalyzed by the catalyst compositions of the present invention. Such isocyanates and diisocyanates may for example include, but are not limited to, the following compounds: a,a'-dimethyl-p-xylylene diiso cyanate, a,a,a1 ,a1-tetramethyl-m-xylyl- ene diisocyanate, &alpha;,&alpha;,&alpha;',&alpha;'-tetramethyl-p-xylyl- ene diisocyanate, &alpha;-methyl-&alpha;,&alpha;'-dimethyl-m-xylyl- ene diisocyanate, bis[4-(l-isocyanato-l-methyl- ethyl)phenyl imethane, a-ethyl-a'-methyl-p-xylylene diisocyanate, 2,6-bis(l-isocyanato-l-methyl ethyl)naphthalene, 1 ,4-bis(l-isocyanato-1-methyl- ethyl) cyclohexane, 1,3-bis(1-isocyanato-1-methyl ethyl)cyclohexane, 1,8-diisocyanato-p-menthane, isophorone diisocyanate, and the like. Many catalysts have been used to accelerate the rate of reaction between isocyanates and hydroxyl-containing compounds. Lead naphthenate and dialkyl tin dicarboxylates are two of the more commonly used catalyst materials heretofore employed for such purpose. Neither of these catalysts, however, when used alone at any reasonable concentration, is effective to adequately accelerate the reaction between hindered aliphatic isocyanates and hydroxyl-containing compounds at temperatures below about 1000C. In accordance with the present invention, mixtures of lead naphthenate and dialkyl tin dicarboxylates, containing from about 25 to about 75 percent by weight of dialkyl tin dicarboxylate, provide reaction rates several times greater than are obtained by the use of either component alone. A preferred composition contains 50 weight percent of each component. Dialkyl tin dicarboxylates, represented by the structure: EMI5.1 wherein R represents an alkyl group containing from 1 to 8 carbon atoms, and R' represents an alkyl group containing from 1 to 18 carbon atoms, are well-known catalyst compounds per se. The preferred dialkyl tin dicarboxylates are dimethyl tin dilaurate and dibutyl tin dilaurate. The lead naphthenate/dialkyl tin dicarboxylate catalyst compositions of the present invention in general may be used effectively at a concentration of about 0.05 to about 5 percent by weight, based on the weight of the isocyanate and the hydroxyl-containing reactants, although in some instances higher concentrations may be used to advantage. The catalyst compositions of the present invention are suitably employed with aliphatic secondary and/or tertiary diisocyanates which are reacted with primary and/or secondary polyols, as commonly used in the art, to produce polyurethane products, e.g., coatings and injection molded products, according to conventional polyurethane technology. Such commonly used polyols include, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1 ,I4-butanediol, 1 ,6-hexanediol, glycerol, trimethylolpropane, p,p'-bis(hydroxyethoxy)benzene, and the like; low molecular weight (mol. wt. 500-5000) polymers or oligomers, such as hydroxyl-terminated polyether polyols, for example, polytetramethylene ether glycol, polyethylene glycol, polypropylene glycol, and propylene glycol/ethylene glycol block copolymers; and hydroxyl-terminated polyester poypls such as, polyethyleneadipate, poly(ethylene-propylene)adi pate, and hydroxyl-terminated polyurethane prepolymers prepared therefrom. The present invention is illustrated by the following non-limiting examples, wherein all parts and percentages are by weight unless otherwise indicated. Example 1 A mixture of 10 grams of dry polytetramethylene ether glycol (OH No. 56.1, mol. wt. 2000), 0.89 gram of a a, a' 1 ,' -tetramethyl-m-xylylene diisocyanate, 3.66 grams of trimethylol propane, and 1.5 ml. of dry toluene was warmed to 73-750C. The warm solution was immediately placed in a calorimeter. To the solution was added 3.6 ml. of a 4$ solution of catalyst in dry toluene (1% by weight, based on the weight of polymer reactants). The temperature initially dropped to 700C and was followed by an exotherm and an increase in the viscosity of the solution. The peak temperature (OC) and the time (minutes) to cessation of flow (gelation time) were recorded. The gelation time provides a measure of catalyst efficiency, with shorter gelation time values indicating greater catalyst effectiveness. The following data were obtained. Catalyst Peak Temperature, C. Gelation Time, Min. Lead naphtalene (LN) 89 3.5 Dimethyl tin dilaurate (DMTDL) 80 2.3 50/50 LN/DMTDL 85 0.6 The data clearly show a marked increase in efficiency, as manifested by reduced gelation time, of the 50/50 catalyst composition. Example 2 The procedure of Example 1 was followed except that dibutyl tin dilaurate (DBTDL) was used instead of dimethyl tin dilaurate. The following data were obtained. Catalyst Peak Temperature, C. Gelation Time, Min. LN 89 3.5 DMTDL 94 4.6 50/50-LN/DMTDL 98 1.1 The data again shows the increased efficiency of the catalyst composition of the invention. Example 3 The procedure of Example 1 was followed except that 3.33 grams of isophorone diisocyanate was used instead of 0.89 gram of a,a,c',a'-tetramethyl-m-xylylene diisocyanate. The following data were obtained. Catalyst Peak Temperature, C. Gelation Time, Min. LN 100 2.10 DMTDL 96 3.60 50/50-LN/DMTDL 75 1.05 Example II The procedure of Example 1 was followed except that 3.22 grams of 1,8-diisocyanate-p-menthane was used instead of 0.89 gram of a1a,a',a'-tetramethyl-m-xylylene diisocyanate. The following data were obtained. Catalyst Peak Temperature, C. Gelation Time, Min. LN 81 45 DMTDL 80 65 50/50-LN/DMTDL 85 4

Claims: WHAT IS CLAIMED IS: 1. A composition for catalysis of reaction between aliphatic hydroxyl-containing compounds and hindered aliphatic secondary and/or tertiary isocyanate compounds, comprising (a) lead naphthenate and (b) a dialkyl tin dicarboxylate in a weight ratio of from about 25:75 to about 75:25. 2. A composition according to Claim 1 consisting essentially of lead naphthenate and dialkyl tin dicarboxylate in said weight ratio of from about 25:75 to about 75:25. 3. A composition according to claim 1 consisting of lead naphthenate and dialkyl tin dicarboxylate in said weight ratio of about 25:75 to about 75:25. 4. A composition according to Claim 1 wherein said said dialkyl tin dicarboxylate is of the formula: EMI14.1 wherein R is Cl-Cg alkyl and R' is Cl-Clg alkyl. 5. A composition according to Claim 1 wherein said dialkyl tin dicarboxylate is selected from dimethyl tin dilaurate and dibutyl tin dilaurate. 6. A composition according to Claim 1 wherein the weight ratio of (a) to (b) is about 50:50. 7. A process for catalysis of reaction between aliphatic hydroxyl-containing compounds and hindered aliphatic secondary and/or tertiary isocyanate compounds in a reaction mixture thereof, comprising incorporating in said reaction mixture from about 0.05 to about 5 percent by weight of the catalyst composition of Claim 1. 8. A process according to Claim 7 wherein said reaction mixture comprises an isocyanate compound of the formula: EMI15.1 <tb> <SEP> R1 <SEP> I <tb> <SEP> R1 <SEP> R1 <tb> OCN <SEP> C <SEP> -arylene-C-NCO <tb> <SEP> R2 <SEP> R2 <tb> <SEP> R2 <SEP> R2 <tb> wherein R1 is hydrogen or C1-C4 alkyl and R2 is hydrogen or C1-C4 alkyl. 9. A process according to Claim 7 wherein said reaction mixture comprises 1,8-diisocyanato-o-menthane.

Inventors: MEGNA, IGNAZIO SALVATORE
Applicants: AMERICAN CYANAMID COMPANY
Application year: 1983
Main classification: C08G18
IPC codes: C08G18, C08G73