[1]0 31152,094 United States Patent Office Patented Oct. 6, 1964 2 Ex'ensive invesfigation of the properties and catalytic behavior of imidazole compounds has now led to the further important discovery that th-,se secondary imidazoles are uniquely thermally sensitive as catalysts, in that even those secondary imidazoles which have quite low activity at room temperature have unusually increased activity -,vith moderate temperature elevation and some of these have at the higher temperature an activity approaching or exceeding the most active tertiary amine catalysts known. Thus, the catalytic activity of secondary imidazoles as measured either by the rate of C02 evolution in the water-isocyanate reaction or as determined by the promotion of reaction between high molecular weight polyols with isocyanates, is increased many fold as the temperature is raised from room temperature (25' C.) to about 75' C. This high temperature coefficient of catalytic activity observed with the secondary im,.dazoles is not found in the case of tertiary amine or other catalysts. This remarkable behavior of the secondary N-imidazoles, without being bound by the theory advanced, is believed to be due to the fact that these compounds are highly associated at room temperature by hydroa,en bondin-. Average molecular weights as hi.-h as 1500 have been found for 4-methylimidazole in 0.6 molar benzene solution at the freezin.- point. With increased temperature, or polar solvation, the avera.-e molecular weight drops (e.g., average molecular weight of 4-methylimidazole in boiling benzene at 80' C. is about 190). As dissociation occurs, more catalyst sites (nitrogen-associated electron pairs) beco.-ne available and the catalytic activity increases. The un-lque properties of these imidazoles that distinguish them from related nitrogen bases are as follows: (1) Their secondary -NH group is inactive ar@d fails to react with isocyanates. (2) The catalyt;c activity of these imidazoles is relatively low at room temperature. (3) The catalytic activity of these imidazoles has a temperature coefficient significantly larger than (at least two or three times as large as) the temperature coefflc-@ent of other nitrogen bases used customarily as catalysts in polvurethane synthesis. (4) Because of this hi.-h temperature coefficient, secondary imidazoles become particularly active at higher temperatures.. say above 50' C., and therefore are particularly useful when used either in cases in which the reaction is carried o,,it at elevated temperature, or in conjunction with other catalysts that initiate the reaction at a lower temperature and provide the heat necessary to raise the temperature to the point at which the imidazoles can develop their optimum activity. The hi,-h coefficient of temperature act,.vation exhibiled by secondary imazoles is beneficially ulilized in accordance w-ith certain as!)ects of the present invention in promoting reactions between isocyanates ar.,d or-anic hydroxy compounds, particu'arly h@'.gh molecular weighl -oolyols, by methods and f rmuiations wherein the cataiytic activity of these imidoazoles is initiated by suitable elevation of temperat,,ire. Such-induction of the catalytic aclivity is broi-i@ht about by provision of a heating medium eyternal to the reaction system or by initiation of an exothermic reaction within the sys@lem as between isocyanate and hydroxyl groups, autogenically or th.-olgh the m-,dium of a co-catalyst havitig sufficiently hig!i a-.tivity at amb'@e,@it tempera@ure. The secondary imidazoles are particLIarly act,.ve in catalyzing the isocyanate-water reaction. They are -enerally less ac,ive thaii sev-,ral of the known polyurethane 1 catalysts i-Ti promoting the polyol-disocyanalle reaction. By uso of th.- two catalysts, i.e., the secondary im-idazole and a hi.-hly active co-catalyst of the 'Lertiary amine type 3,152,094 PRODUCTION OF POLv.-UP@E, THANES USING AN PJMAZOLE CATALYST 'VVH]iam E. Erner, Vl;ilmington, De]., and Harold A 5 Green, EEdns Park, Pa, assignors to Air Product; and Cheml'tcals, Inc., a co.,-poration of Delaware Eled Aug. 26, 1960, Ser. No. 52,053 23 Claims. (Ci. 260-2.5) The present invention relates to the production of poly- 10 uretha ne high molecular weight condensation products and is particularly concemed with formulations for such produ cts employing novel catalysts of selected activity for promotin- the reaction between the or.-anic polyisocyanat e and the organic polyhydroxy compound in poly- 15 uretha ne foams as weH as in non-cellular products, and/or the reaction of the polyisocyanate with water releasinC02, which serves as a blonving agent in expanding the resin in the case of such foams. The non-cellular polyuretha ne products include elastomers, coatings, adhesives, 20 films and the like. Polyur ethane foams, both of the ri.-id and ffexible type, are well knoivn as products of reaction of a long chain polyol resin with an organic isocyanate, most usually an arylen e diisocyanate. Typical formulations used in the 25 prepar ation of such foams include as essential components a resin containing tnvo or more hydroxyl grolps per molec ule, a diisocyanate and a catalyst. The blowing agent may be a gas, such as C02, formed in the reaction as when water is included in the formulation to react 30 with isocyanate groups, or an external blowing a.-ent may be included in the form of a liquid capable of vaporiz;n,@ at or below reaction temperature, such as Freon. Amon g the more gencrahy employed polyols that have been employed in polyurethane foam formulations are 35 hy&o xy-terminated resins such as (1) hydroxy polyesters of from about 500 to 5000 molecular wei,-ht prepared by esterification of a polyhydric alcohol (with or without ether linkages) and a polyfunctional carboxylic acid, or (2) polyalkylene ether glycols of from about 500 to 40 5000 molecular wei.-ht. Cataly sts previously found effective in polyurethane foam formation have been of the tertiary amine type. Amonthese, there have been chiefly employed in commercia l foam formulations N-alkyl morpholines, triethylamine, and, more recently, triethylenediamine (1,4-diaza- 45 bicycl o-(2.2.2)-octane). Secondary amines and, in general, those compounds containing the groupin.- of -CNH-Chave been described by workers in the art as unsuitable 50 for use as catalysts in polyurethane polymer formation, since such compounds having secondary amino groups are elimin ated by reaction with isocyanates to form ureides. In prior patent application Serial No. 804,884 of Harold A. Green, filed April 8, 1959, and now abandoned, of 55 which the present application is a continuation-in-part, there is described the use of 2-alkyl imidazoles as catalysts in production of polyurethane foams. The present inventi on is based on the discovery that not only the 2- alkyl imidazoles, but also unsubstituted and more high- 60 ly substituted secondary imidazoles exhibit useful catalytic activit y in polyurethane formulations utilizin.- reactions betwe en polyol compounds and organic diisocyanates. By secon dary imidazoles is meant those imidazoles wbich contai n hydrogen on the secondary nitrogen of the ring. 65 These secondary imidazoles are unique in that, contrary to expect ation and in contrast to other secondary amine compo unds in general, they do not react with isocyanate to form ureide, which would become incorporated in 70 the polymer and thereby be removed from the catalyst system.
[2]3 or of the nie' al salt t-,, e (t,n soaps or tin salts, for , p example), greater flexibility is prov;ded in controllirg the properties of the ultimate foam, sinc.- thereby the rate of the water-diisocyanate reaction (blowirig) can be regulated somewhat independen-'Iy of the poly ol-d-@isocyanate (condensation) reaction In accordance with another aspect of th-. present invention, polyurethane foam compositions ar@- provided coqtaining secondary imidazole as catalyst alone or in combination with more active calalysts promoiing acc-lera10 tion of the reaction betwee-ii polyols a-@id organic di-'@socyanates. In one preferred embodin. eit of the - inven'Lion, the more active catalyst is a hi-,her aliphatic carboxylic acid salt of stannous tin. The high temperature coefiicient of activity is advan1,5 tageously utilized in co-catalyst systems in that the exothi@rm obtained by initial react;on in the presence of the more active co-catalyst raises the temperature of the system to a s@dfneient degree to activate the secondary imidazole as a catalyst. -@0 The temperati-ire act;vation of the secondary imidazoles can also be utilized to advantage in single catalyst systems wh@@rein delayed action is desired in foam production, for example, in production of foamed products from wamed mixes. 25 Th,- secondary imdazoles which can be utilized in practice of the present invention corresioond in -Cneral to the formula H 1 30 RI-C-N (1)--- (2) C-R2 (4) (3)5:@--- RR-C-N in which RI, R2, and R3 are hydro.-en, alkyl or benzyl, or RI and Rg together form a tetramethylene chain attaching to the indicated 4-5 positioils of the imi-dazole nuclelis as ip the case of I12C / \ H H20 C-,N 40 C-R2 112 C C-N c H2 45 4,5-cyclotetrame'Lhylene imidazoles (tet rahydrobenzimidazolcs) in which up to 2 of the hydrogens at+ached to carbon of the tetramethyleri-. chain r-nay be replaced by methyl. The preferred compounds are those iLi which there is 50 present on at least one of the pos;tions 2, 4, 5 of the imidazole ring a short cha,.1i alkyl substituent and the total number of carbon atoms included -in the substitue-.its Rl, R2, and R3 does not exceed 12. Amon- other C-hydrocarbon substituted secondary 55 im;dazol@s which have been found temi)e rature-sensitive in promotin,@ polyurethane reactior@s, there are iicluded: 2-Dropyl @.Midazole, 2-butyl imidazole, 2-benzyl imidazole, 2-benzyl 4-methyl imidazole and 2-butyl 4-methyl im;dazole. Those compounds in Nvhich the total nuriiber of 60 carbon atoms contai-iied i-ii the substituei-its RI, R -tnd R 2, . 3 exceed 12, while ooerative as catalysts in promoting the hydroxyl-isocyanate reaction, are of comparat-@ve'@Y low activity even at the higher temd@-ratures 'as,-d in practical operat@'ons, and are less preferred. 65 The secondary imidazoles can be prepared in general by the methods described in Erner, U.S. Patent No. 2,847,417. Thus by reaction of 2,3-diamino-butane with acetic acid, 2,4,5-trimethyl imidazole is obta;ned. The correspondi.ig triethyl compound is formed from 3,4-di70 amino-hexane and propionic acid. VVhile numerous polyisocyanates have b.-en suggested as suitable for reaction with the polyols to produce urethanes, including naphthale-.le diisocyanates, hexamethylene diisocyanates, and even certain aliphatic diisocya75 4 nates, most commercial foam formulations employ toluenediisocyanate generally in the form of the 2,4-isomer with or without inclusion of a lesser amount of the 2,6-isomer. in typical practice for foam production, using the "oneshot" technique, aR of the ingredients except the isocyanate are premixed and the latter then added to effect reaction. In other systems, all or part of the isocyanate is pre-reacted with the polyol to produce an isocyanate terminated prepolymer, which is then reacted with additional reactant such as water in the presence of catalyst to obtain foams of desired properties. The following 13 examples relate to foam production. Example I The components used in the formulation were: Parts by wt. Diol-PPG 2025 1 ----------------------------- 200 Triol-LG 56 2..................................... ............ 100 Tolylene diisocyanate (TD 80) 3................... ................. 115 Organo-silicone stabilizer (X-520) - - ------------. 1.5 2-methylimidazole -------------------------- --.......... 4.5 Waller --------------------------- -----------. 8.7 Diol-PPG 2025 is a polypropylene glycol of about 2025 in@lecular weigbt. - Triol-LG 56 is a -lycerine polypropoxide triol of aboiit 3000 inolecular weight , and having a hydroxyl iiumber of 56. -TD 80 is a mixture of 80% 2,4-isomer with 20% of the 2,6-isomer of tolviene diisocyanate. 4 X-520 is a sflicoile compound made by blocked polymeriz,,Ltion of a polypropylene glycol with dimethyl silicone. The 2-methylimidazole was first dissolved in the water and the solution bl-.nded wi+,h all of the other components except the diisocyanate by mixing with a high speed agitator for five seconds. The diisocyanate was then run into the dispersed mixture with further agitation for five seconds. The mixture was then poured into a mold. Creaming was almost instantaneous. Maximum foam rise was noted at about 2.5 minutes. The obtained flexible foam showed good cell structure, good stability and negli.-ible shrinkage on aging. In the above run a polyetber type polyurethane foam was produced by the "one-shot" technique, which type of operation has b,-en possible heretofore with only few of the catalysts otherwise useful in pqlyurethane formulations. The hydroxy pol I yethers typically employed in polyurethane foam formiilations have molecular weights of 2000 or more and are of a type including recurrinc-, [O-C-C-O-.C-C-O] V y groups in which y is H or methyl. Example II The components used in the formulation were: Parts by wt. Polypropylene glycol (PPG 2025) -------------- 1 200 Triol@LG 56 ------------- ---- 100 ---------------- Tolylene diisocyanate (TD 80) ----------------- 115 S-'I,'cone stabilizer (X-520) --------------------- 2.2- Triethylene diamine --------------------------- 0.6 2-methylimidazole ---------------------------- 1.5 Water -------------------------------------- 8.7 The two catalysts (triethylene diamine and 2-methylimidazole) were dissolved in the water and rnixed with the other ingredients except the isocyanate, which latter was added after initial rapid agitation and the mixing continued at 875 r.p.m. for 5 seconds. The mixture was poured into prepared molds. Cream time was almost instantaneous with maxiinum foam rise occurring in 60-70 seconds. A foam of well developed cell structure and good stability was obtained. By the ii-se of the alkyl imidazole as co-catalyst in the above formulation the quantity of triethylene diamine was reduced to about one-half the amount that would be
[3],9, 1 @r- 2,09Arneeded in this formulation il' used alone. Similar reduction in the quantity of tertiary amine calalyst by replacement wi+h alkyl imidazole is i)ossible in typical formi-ilations made with sorbitol polyciers. In the fore.-oing examples, the preparation of "onesho,+," polyether foams is described. It will be understood that th,- us,- of the alky'. irridazole as catalyst or cocatalyst is not limited thereto, but that the alkyl imidazole can be substituted in whole or part for the tertiary amine catalyst used in conventional polyether foam formulations usin@ the prepolymer technique. The alkyl imidazole can also be used in polylrethane foam products based on the use of polyester intermediates such as those derived irom Dolymerized higher fatty acids (dimer acids), reaction pro@ucts of a polyhydric alcohol or polyhydric etheralcohol with a polycarboxylic acid, such as die@hylene glycol adipate, etc. Example III A typical formalation for an ester type flexible polyurethane foam is as follows: Parts by wt. Hydroxy polyester resin (hydroxy No. 60-65) mol wt. about 3000 ----------------------------- 100 Tolylene diisocyanate --------- ----------------- 28 Lecitbin ------------------------------------- 5 2-methyliinidazole ---------------------------- 0.7 Water - -------------------------------------- 1.5 A hi-b'@y critical evaluation oi' polyurethane condensation catalysts is obtainable in the continuous production of uniform polyurethane foam on the moving belt of the commercial foa-in machine. In this operation the reactants and catalysts are continuously proportioied into two streams vihich are mixed at hi,-h st)eed and ejected through a no-7-7Je onto the moving belt. E.Yample IV The eeciency of the alkyl imidazole catalyst was demonstrated in machinemixed "one-shot" flexible polyether polyurethape foams in a number of runs, of which the following are typical. The polyol was charged at the rate of 4300 grams/min. into the mixing head, and separate streams of the TDI and of the mixture of catalyst and stabilizer in water run into the same mi-,ung head and e,;ected continliously on the moving belt. Foaming and curin.- proceeded as the belt moved away from the im,xin.- nozzle. A B c 0 Diol-PPG 2025 (parts by weight) 71.5 71.5 71.5 71.5 Triol-LG 56 (pa-ts by @;7eight) --- ---- 28.5 28.5 28.5 28.5 TD 80 (parts by weight) ------------- 36.8 36.8 36.8 36.8 Silicone X-520 (parts by weight) - ---- 0.7 0.7 0.5 0@@ Wat@r (parts by iveigbt) ------------- 2.95 2.95 2.95 2. c) 2-methylimid@,zole (parts by ivei ght) 0.5 0.7 0- 7 -------- - Triethvleiae diamine (parts by v,-eight) ---------------------------- 0.2 -------- -------- 0.2 Appearance, Opeia Cells, Percent -- -- 100 100 100 100 Physic@@l Properties (Cured 3 hrs. at 250' F. ambi@,nt htimidity): Den--ity (lb./ft.3) ----------------- 2.01 2.61 2.04 2. 62 Tensile streiagth (p.s.i.) ---------- 19.2 13@ 6 8.80 13.2 Tear resistance (lb./iia.) ---------- 3.45 3.10 2. 60 2.25 Comp,ession Lo@d (p.s.i.) for 25% deilec-tion ----------------- 0.29 0.28 0.28 0.35 Compression s--t at 50% defleetioi2, Percent on origiiaal he'@ght- 6. 7 1 10.0 12.4 1 7.8 Because of the described unique prop,-rty of these secondary Nimidazoles, they are r)arlicularly advanta,@cous ivhen used in combinat;on w@th slannous soaps in polyil-rethane foam for@-@iulatioris. Stannous octoate, for example, has exceptionally high activity in promoting poly-r,aer growth in the polyol-isocyanate (urethane) reaction. For example, the viscosity of the urethane mix containing stannous octoate goes from about 300 centisto-l,es to about 900 in ten mi@lutes, reachin.a 2000 or more in less than 18 minutes. T-n comparison, a urethane mix containin.- dibutyl-tin dilaurate after 20 minutes reac'ned a 6 viscosity of only about 700 centistokes, and dibutyl-tin dioctoate (2-ethyl hexoate) was even less active. On the other hand, stannous octoate is comparatively poo@.- as a catalyst in promoting C02 evolution not only when compared w@th the dibutyl-tin salts R2Sn-(OOCR')2 but even as compared with the relatively low activity tertiary amine catalysts such as N-alkyl morpholines. By combining the stannous soap, which is highly active at ordinary temperatures and highly selective for the ure10 thane condensation reaction as distinguished from the blowing (ureide) reaction, with a secondary imidazole, which is hi,-hly temperature sensitive and thereby effective in promoting the latter reaction. in selected proportions, there is obtained a very desirable added factor of flexibility 15 in regulating the timing and rate of these two reactions which can be u-'ilized in controlling the desired properties of the ultimate foam. The stannous soaps provide the initial catalysis Lor chain .-rov,7th and thereby furnish the exothermic heat for triggering the catalytic action of the 20 secondary imidazole. In this combination the advantage of time delay in foaming is particularly evident. When the stannous tin soap is used as co-catalyst the polmerization reaction has a head start over foamin- since the tin soap has little activity in promoting the - wa@ter-isocyanate 25 r@-action. Greater production (pounds of foam mix per m@ inute) can thus be obtained from a given machine. When the secondary imidazole is thermally activated it not only catalyzes foamin,- but also augments the urethane condensation reaction thus acceleratin.- curing of the foam. 30 The combination of these catalysts thereby obtains a balanced finished product. The stannous soaps and secondary imidazoles are chemically and physically cornpatible. In use these may be introduced separately, together, or in various combinations 35 with the other ingredients of the formulation. The liquid sta@mous soaps have good solvent properties for the imidazoles even at roorintenperature. If high concentrations of the imidazole are desired beyondtheirsolubility in the stannous soaps, inert solvent may be added, such as di40 pnenyl ether, to render the combination liquid at room temperature. Typical formulations employing the above-described catalyst combinations are illustrated below: Example V 45 Flexible foams were produced by the "one-shot" technique from the following formulations: 50 Parts by weight A B Polypropylene glycol (2,000 M.W.) -------------- ---------- 72 Triol-LG 56 ------------------ --------------------- 100 28 55 T olyiene diisocyanate (TD 80) --------- ----------- 37 3 7 W ater__ 2. 9 2 9 Org ano--fflc--o-n-e- -oi-I ------ ------------------------------ 1.0 l'O 2- methyslimidazole ------ --------------------------- 0.3 0. 3 Stannous octoate (2-ethyl-hexoate) - ---------------- 0.2 0.4 60 Forrnuta A was used in a hand-mix operation and Formula B in a machine operation. The latter had a r-ream tlr@ie of 16 seconds and a rise time of about 115 seconds. Both of these foams were rapidly self-curing, of good structural uniformity free from fissures and scorch65 in,-, showing the characteristic sticky skin. This skin stickiness was quickly clared by brief heat treatment at 70-125o C. in hot air. These foams had - a density of about 2.3 lbs./ft.3 and their load bearin.- characteristics were very -ood. The thermal "trig-,ering" of the inlid70 azole catalyst was exhibited when the slowly rising foam suddenly accelerated and thereafter rapidly completed the foaming and curing process. By the inclusion of auxiliary blowing agents, such as 10 parts of Freon or propylene oxide, in the above formula7,5 tion the foam density was reduced to 1.45-1.50 lbs./ft.3
[4]7 while retaining reasonably good load-bearing characteristics. Example VI A "one-shot" rigid foam of good closed ceU structure, dimensional stability, and fastcuring properties was produced by the following formulation: Parts by wt. Prodendrosorbitol (G 2410) 1 ------------------ 300 Tolylene diisocyanate (TD 80) ---------------- 248 Trichlorofluoromethane (Freon 11) ------------- 45 Organo-silicone oil (X 520) ------------------- 3 2-etbylimidazole ----------------------------- 0.52 Stannous octoate ----------- ------------------ 0.15 '. Sorbitol-polypropylene glycol of about 760 molecular weight, hydroxyl number 495, acid nudaber 0.34. All of the ingredients were blended for fifteen seconds and -then poured inlo a mold. Initial creamin-. was noted in two minutes. By three minutes, creaming was completed and the niix started to rise, reaching flill height and geeing in four minutes, and becoming quickly tack-free. Example VII Good rigid foams were r.-adily mixed and prc-duced witn a triol (containing about 20% diols) of about 150 eq,,iivalent weight and having a hydroxyl number of 375, based on glycerine copolymerized -,vith ethylene and propylene oxides (Dow ET 390-421); when cutting the to'tal catalyst concentration to about 0.1 part per 100 of the polyols (in the ratio of about 3.5 parts 2-ethylimidazole to 1 of stannous octoate). Foaming in this instance be.-a-n in 60 seconds and was complete in 100 seconds. Example VIII Good foams were produced using unslbstituted imidazole as catalyst; an example of which follows: Parts by wt. LG 56 -------------------------------------- 300 TDI ---------------------------------------- 112 Trichlorofluoromethane ------------------------ 10 hnidazole ----------------------------------- 1.5 Stannous octoate ---------------------I-------- 0.9 Water ----- -------------------------------- 8.7 SiEcone off ------------ L --------------------- 3.0 This mixture had a cream time of 20-30 seconds and complete rise in 170 seconds. It was somewhat slower curin- than the foams prepared with 2-niethyl or 2- ethylimidazole. The skin tackiness was readily cured, ho,@iever, by heatin,-,at 120' C. for one hour. The foam was of low density, i.e., 1.6 lbs./ft.3. Example IX A number of runs made on the foam machine indica'Le that the combination of secondary imidazole with stannous octoate as catalyst produces foami s equivalent in strength and load-bearin-. characteristics and in compression set, to foams produced from similar formulations employing diazabicyclo octane cawyst. The stannous octoate-secondary irnidazole system may be advantageous froni the standpoint of somewhat longer cream and rise tinie. The foaming systems using the combined catalyst were extremely stable and less apt to develop side splits or other .physical defects with changes in machine conditions frequently encountered in systems employin.- a single catalyst. Four separate runs were made on the machine from the fohowing formulation. All runs produced good foams free from visual defects. Parts by wt. Polypropylene glycol (LPG 2025) -------------- 72 Triol (LG 56) ------------------------------ 28 Tolylene diisocyanate (TD 80) ---------------- 36.6 Water ------------------------------------- 2.9 -Soluble silicone (XL 520) --------------------- 1.0 Stannous octoate ----------------------------- 0.4 Imidazole ----------------------------------- 0.3 3,152,094 Th-- nozzle was op.-rated to inject part of the water containing the comb,.ned catalysts at an upper level and the remaining water containing the silicone at a lower level. The several foams produced had cream times of from 9 to 15 seconds and rise tipies of 120 to 128 seconds. The physical properties are tabulated below. Each of the foams prior to testing was given a I hour cure at 250' F. and anibient humid-ity. 10 A B 0 D D,-nsity, lb.ift.3 ---------------------- 2.01 2.09 1.93 2.08 Tensile strength, D.s.i ---------------- 10.4 12.6 22. 6 22. 5 15 Tear resistance, IS./in ---------------- 2.6 2.6 4.5 5.0 OGmpression-deflection, p.s.i.: 25% ------------------------------ 0.39 0.38 0.41 0.45 50% --------- 0.48 0.48 0.50 0.55 65% ------------------------------------ 0.58 0.60 0.63 0.71 75% --- ---------------------------- 0.81 0.81 0.81 0.93 Compression set at 50% after huinid 20 aging (22 hrs. at 1581 F., 5% relative hun,.idity): Percent origirial beight ----------------- 7.0 8.9 5.9 6.9 Example X - 25 The 'Lollowin-, formulation may be employed for preparation of quick@setting ri-,id foams from alkyl ester resitis of high hydro:@yl number. Parts by wt. 30 Glyceryl adipate phthalate (from 4 mols glycerine, 2.5 mols adipic acid and 0.5 mol phthalic alihydride; hydroxy number aboiit 301@, acid number ab-out 12, 0.4% H20) ---------------------- 100 Tolylene diisocyanate ------------------------- 80 Water -------------------------------------- 2.05 35 4-methylinijdazole --------------------------- 0.15 Stannous octoate ------------------ ----------- 0.30 The resin is mixed with the diisocyanate and the remaining ingredients added as an aqtleous solution which is 40 blended in by stirrin.-. The reaction mixture warms up in about 1 to 2 rninutes at which time it is poured into a mold. The mixture therein foams and forms a stable ri,-id product in 1 to 3 minutes, which is self-curing. Curin.- and surface hardening can be accelerated, if de45 sired, by heating the product in an oven at about 120' F. I to 3 hours. Ready-mix--d catalyst combinations for various typ.-s of formtilations may b-. prepared by dissolvin.@ +,he sec- - ondary imidazole in the liquid starmous soap. At room 50 temperature 20-30% by weight of the 2-methylimidazole will dissolve in stannous octoate; at 97' C. as much as 43% by weight will be dissolved. 2-ethyliriiidazole 4s more soluble, obtaining 43 % concentralion at room tem- -perature. Equal parts of 2-methyl- and 2-ethylimidazole 55 are soluble to 43% concentration in s'@alinous octoate at 45' C. For most typical formulations the imidazole/ stannous soap wei.-ht ratio will lie in the range of from abotit 0.511 to 511, and the combined catalyst wifl be used in amounts of from about 0.25 to 1.0 part p--r 100 of 60 pojyol. A convenie-lit catalyst combinatio@i for wide use may be rnade up by compositin.@ 3 parts of seco-,idary iniidazole with 1 to 2 parts of the tin soap, and sufficien@, in.-rt solvent added to maintain t'@le two in lic,,uid solu65 tion at a@oout room temperature. This will require addition of about 2 -varts of dio'iie.-iyl ether. Otl@ier inert solvenls include d-loxaiie, d@'.e,hylene glycol dimethyl ether, butyl phthalate, 2-ethy'@-hexyl furiiarate, ce. Reactive solveits such as dipropylene glycol, PPG 2000, 70 etc. may also be used -.n silitable instaices. If it is desired to ernploy a hi-,her rallio oj' imidazole to stannous soap tnan that contailed in tne ready-mixed catalyst soluion, the same ca.1 be a,-ijusted by further addition of more imidazole i@i the desired qucitity i-.i the ri-lixing or 75 added to one of the co.-P@patible cornpo@ients of t'.I-- mix.
[5]9 Examples of other sLaTinous soaps that can be similarly employed include: Sl@annous laurate Stm-inous decanoate Stannous azelate 5 S'Lannous myristate, etc. Stannous oleate B.-sides imidazole (which has a secondary-N strueare substituted only in the 2 or 4 position, there may be employcd secondary imidazole co-,npounds containing the alk@,,l substituent -in the 5 position or those haii-,ig, in additioil, an alkyl or non-inlerf--rin- non-funciional substituent on one of the other carbois of the rin.a, such as 15 2,4-dimethylimidazole; 2-ethyl-, 4-methylin-iidazo'@e, etc. These, as w,-Il as 2-ethylimidazole, have low - meltii,-,- poipts and may be desirable i'Or that reason in marketing ready-ILO-use liquid catalyst combinations with tin soaps. 20 For advantageous use as as co-catalysts in the system with se-,onda,-y im-'@dazo@ies wher,-in it is desired to develod th,- required exotherm for initia@iig catalyst activity of the imidazole, the:,-e came into consideration tho.,e catalysts of hi,-h a@tivity at roon lemp,-rat-are which -X- 25 b '.bit raoid development of an exoti-emiic rise in 'Cmp.-rature of the reaction mixture, including diisocyanate and polyol, at least in the maa,nitude of 0.1' F./see., of N@,hich the tin co@npounds and 1,4-diazab icyclo-(2.2.2)- octane are representative. 30 A -'Loa-rnin.- composition t@,lat perrnits hard-nux,.n,@ of potyurethane i@igredients in small lots has long be.-n souglit for ciistom shops. NV,'iereas i-ii machiiie runs of slab fo@)res as on the Bayer-Henneeke machine rapid mixhng and reac@'L-lon are esselitial, such operatio-@i is 35 suited or.,Iy to mass productio-@i o'l a uni.Forr@n - slab-foa-m stock. The catalyst-isocyanate-polyol-waLer and silicone are mixed in the machine nozzle and deposited on the movin- belt as a "creamir.,g" reactive n-lixture within less than a second ol' elapsed time. 40 In such app'ications, secondary imidazoles as a grotip are far less active a-,id therefore not co-risidered practical. However, with tfie use of "slow" secondary imidazo'@es and thermal activation, foam manufacture can be safely and successfu-lly done on a custon shop bas-.s, 45 as seen -'Lron the followin.- illustrative exam-Die. Example XI Parts by wt. PPG 2000 ----------------------------------- 100 50 @ T 37 .D - --------------------------------------- Orga@io-sil-icon.- (DC 199) --------------------- 0.5 Imidazol. - ----------------------------------- 0.5 Water -------------------------------------- 2.9 Th-- tolylene diisocya-.iate, silicoie and imidazole are 55 mixed and heated to effect solution of the catalyst. At a temperat@,jre o' . about 70-75' C. a solu',ion of polypropylen-, -lycol and water is added with e-gective mixin@- of the two reacta-nt streams, as in the - Bayer-Hennecke maenine. The creamy mixture is pump--d into 60 molds or onto a slabbing belt and the foam product formed, rising to maximum height in 2 minutes and selfcu.-ing in 60 minu@,es. From nunierous other runs on machine-made -,9exible ans, it was observed that the foaming system er@iploy- 65 .Lo in.- pro!)er ratios of tin sa:t and secop-dary -.rmdazo'e was e,-,ceotionally stabl@e froin the standpoint ofduplication of results and these niixed ca+,alyst systems (with secor,.dary imidazole) were less sensitive to changes in mach;n,- conditions often found to give rise to development 70 of physical defer-ts when employin.- tertiary amirie or metal salt catalyst alon,-. A cream time of 8-12 seco.--.ds with a rise time of 80-120 seconds, ootained in tl-.cse irixed ca@alyst systems, is especially desirab-I.ffor continuous rnachine production of flexible i'Oanis. The 75 bet+lcr Dhysical properties of the -nixed catalyst syster@i usin.@ secondary imidazole are paxtic-alarly evident in the samples employin.- higher levels of tolylene diisocyanate. The exceptiona'lly hi,@h activity ol' the secondary trialkyl imidazo'@es at elevated temp-..-ature renders tlese cor.-ipounds especially desirabl-. for us-- iii a machi-@icless pot mix method for maling ioams, taking advantage of the slow creamin.- at room temi)erattir,- and rapid catalysis a-'Lter the system is warnied by co-catalyst add@tion E x a m p l e X I I P a r t s b y w t . Dow 11-300 resin (glycerine triol) -------- ----- 300 TD '00 ------------------ ------------------ - 105 Orga-iiosilicone (DC 199) ---- ---------------- 3.0 2,4,5- trimLtiiylimid azole ---- ------------------ - 1.5 Weer ------------------ ------------------ -- 9.0 The catalyst was dissolved in the resin follov,,ed by the or.-ano-silico@-ie and the diisocyanate then stirred inl,o the mixture with a spatula until a homo,-CneG-iis composition was obtaiiied (about 10 seco.@ids). The water containinl- a s-mall amount of water soluble polyethylene -lycol polyir@.-r a.- a tl,-ickener, was thcn added and stirin., continued for 45 seconds until creainiig was evident. Tne mix was poured i,-ito an open boA mold wher-@ foarling continued to reach full heiot in about 135 seconds. The foarned product was surface-c@,ired in an oven at 70' C. E x a i - t 2 , g l e X I I I I-Ti 300 graw-s of glyceri-,ie propo:-,ide triol (LG 56) ther.- was dissolved with stirrin., a.id -entle warming 0.9 gram of 2-.-i-eihyl-ictrahyd rob.-nzimidazole. After coolin.- the solution, there were dissolved therein with stirring 3 grams of or.-ano-silicon (DC 199) and 0.3 gram of stannous o-.toate, followed by consecutive addition of 108 _uams tolyler.,e diisocyanate (TD 80) and 8.7 grams of water. The mixture was well s'lirr,-d for e,@,@ht seconds and poured into a mold. A smoothly rising foam resulted, which became tack-free rapidly and showed good elastic properties. The choice of any particular secondary imidazole may vary with the system or forr@iulation in which it is to be used as well as with the procedures utilized and the desired properti@@s of the ultimate product. For use i@-i the production of polyur.thane plastics or elastomers by the conventional reactio-.1 of an organic polyisocyanate, typicaey tolyler@c diisocyanate, with a high molecular weight polyol co@npound such as polyhydric alcohol, ether alcohol, or ester; the pre.Lerred compoi,- nds are those in Nvhich the hydrocarbon substituent attached in one or tnvo of the positions 2, 4 and 5 on the imidazole ring is an alkyl group of one to two carbon atoms (methyl or ethyl), these be;ng more active as catalysts than ur@substituted imidazole and than the corresponding aryl imidazoles or the higher alkyl imidazoles in which, for example, phenyl, octyl, nonyl, or heptadecyl groups arepresent. V@7hile the catalytic activity of the imidazoles at suitable temperature may also be evidenced in other related reactions betwee-.i or.-anicisocyanates and compounds cortaining an active hydrogen (as deterniined, for examt)le, by the Zerewitinoff method) including among the;e compounds cortaining typically hydroxyl, carboxyl, primary or secondary amino groups, the chief practical interest lies in the use of these secondary imidazole catalysts in reactions betN@/een or--anic isocyanates -,vith polyol compounds, these bein.- presently most L@nportant commercially in connection with the production of various flexibl,- and rigid polyurethane plastics, including polyurethane coatin.-s and clastomers. Typical polyol compounds whl:ch have bee@i used in high molecular @,,,eight polyurethane plastic and resin compositions i-@iclude: tu-,-e) and the secondary imidazoles named above vihich jo or application o'l external h-,ating.
[6](a) Hydroxy polyester compounds illustrated by esters of polycarboxylic acids with polyhydroxy alcohols (alkyd resin type) in general and partielilarly adipates and phthalates of -Iycerol, glycols, and of glycol ethers; hydroxy esters of dimerized hi,@her fatty acids with dihydric 5 or polyhydric alcohols. (b) Polyether glycols (diols) of 500 to 3000 or higher molecular weight, for example, 1,4-butyle-@ie oxide polyglycol and mlxed polypropylene-polyethylene glycols; socalled "trials" form.-d from trifunctional polyols by con10 densation with ethylene oxides and/or propylene oxide, using as t,-ih@ldroxy base glycerine or trimethylol propane; as well as higher hydroxy compounds based on hexahydric alcohols such as sorbitol. (e) Glycol, -,Ivcerine or other polyhydric alcohol de- 15 rivatives of alkylene polyamines, such as N,N'-tetrakis(2-hydroxypropyl) ethylene diarnine. (d) Castor oil and its derivatives includi-@ig ricinoleic acid esters ricinoleyl alcohol and condensation products of castor oil with glycols or witn diglycolic acid. 20 Vlhile tolylene diisocyanate has been tne one most frequently employed iii foamed polyurethan,-s, particularly as mixlures ol' 2,4 and 2,6 isomers, these, as well as other organic poly;socyanates, have been used in noncellular polyurethane formulations of var@'.ous types, in- 25 c'.uding, for example: m-phenylen,- diisocyanate, hexamethylene d@';socyanate 4,4'-methylene b-s-(phenyl isocyanate), naphthalene diisocyanate, - -triphenylmethane triisocyanate. Also included are l,h-- prepolymers having terminal isocyanate groups formed by condensation with polyols, and the dimers and trimers of aryl diisocyanates. The above examples of polyols a-@id polyisocyanates are merely illustrative o'L the wide range of formulations in which the catalysts of ihe inveiltion can be employed in non-cellular polylirethane formulat;o@l and are by no "@ing, rneans iitended as exhaustive or limi Iti fact, the mixed catalyst systems described can ger,.erally be substituted, with greater or lesser advaiita.-e, in most known formulations emt)loying ac@tive catalysts for promoting polyurethanereaction. In those instances in which there is no active co-catalyst eniployed in the formulation to provide the required temperature elevation 'lor initiating the activity of the secondary im;dazole, all or part of the components and da reactants to foriii the desired polyuretnane may be admixed with the iriidazole at room temt)erature and the mixture then heated in any suitable manner to required react-,on temperature, as above about 50' C., or the mixing itself may be carried out at kdpropriate elevated 50 temperature to effect th- desired reaction. In those forrnulations in which an active co-catalyst is employed, which has the reqlired activity at ambient temperature, external heating will not ordinarily be required to initiate the reaction, although in some instances additional heat- 55 ing may be desirable to shorten th,- ui@timate curin- time Reference has been rnade to the use with the imidazole: for providing temperature elevations by - exothermic reaction, of co-catalysts which are active at low or room temperature. The.@e are vanous ways known in the art 60 for testin- or dete-mining activity of cataly@-ts, many of which are' described in tne literature [see, for example, A. Farkas and K. G. Flynn; 1. Am. Chem. Soc., vol. 82, p. 642 (1960); and literatiire references there cited]. A familiar test of catalyst activity for promoting th.- iso65 cyanate-hydroxyl (urethane) reaction is based on the determination of rate constants for given catalysts at seIlected concentrations in promoting reaction of a model system compris I in@- phenyl isocyanate and 2-ethyl hexanol -in sta-@idard solvents (benze-Tie or dioxane), as compared 70 viith the uncatalyzed reaction. In these tests triethylene d-famine (1,4-diazabicyclo-(2.2.2)-octane) has been found to have an activity of at least 4 to 5 tirnes as great as other commercial tertiary an-iine catalysts tested; only the metallic catalysts, such as stannous bctoate and di75 butyl tin dilaurate bave been found to bave the high order of act-lvity comparable to 1,4- diazabicyclo-(2.2.2)octane. Other known tests of catalyst activity in the urethane reaction utilize as the model system polypropylene ether glycol and tolylene diisocyanate. Activity of the various catalysts can be compared by determinin-. the - .nerease in viscos;ty of the reaction mixture as a flnetion of reacting time. By comparing the rate of viscosity iicrease for the system at room temperature for any given catalyst with that exhibited by the same catalyst at higher temperatlre (genera at about 7 ' C.) e therma coei'i9c@.ent of activtiy can be determined for that catalyst. Instead of rneasurin@., the rate of viscosily increase at a given temperature, the activity of polyurethane catalysts can be compared on the basis of their effect on the rate of exothermic heat evolution in a model system. A typical test system is one employing 350 grams polypropylene glvcol (M.W. 1000) and 117.5 grams of tolylene diisocyanate (80-20) to which the catalyst is added in Celloso'.Ve acetate solvent. Based on observed data at 0.1% catalyst concentration, respectively, (a) during the first 15 seconds and (b) to time of reaching maximun-i temperature, of niimerous commercial catalysts tested, only stannous octoate, dibutyl tin dilaurate and 1,4- diaz,,ibicyrlo-(2.2.2)-octane showed rates of temperature ris.- in excess of 0.10 F. per second, rati-iig i-@i the order nomed. The others includin,@ tetramethyl butane diamine, triethyl amine and N-ethyl morpholi-@i-., showed activity levels of less than half that of 1,4-diaza@oicyclo-(2.2.2)ctane. Takin@ the uncalalyzed reaction as unity, these catalysts showed an order of reactivity in the 15 second exotherm test as follows: TABLE 1 Order of Rate, Reactivity F./sec. St,,tniaous octo-ate -------------------------- 200 0.20 Dibutyl tin d-@laurate ---------------------- 200 0.20 1, 4-diazabicyclo-(2.2.2)-octane -------------- 150 0. 15 Tetramethyl but,,ine diamine -------------- 67 0. 067 Triethyl amine ---------------------------- 60 0.060 in-ethyl morpholine ----------------------- 50 0.050 At 0.5% catalyst concentration, stannous octoate and 1,4-diazabicyclo-(2.2.2)-octane showed activity levels in the 15 second test ol' over 5 times the mag-iiicade of the other three amine catalysts listed above, while dibutyl t-in dilaurate fell below 1,4- diazabicyclo-(2.2.2)-octane, but still showed several times the magnitude of the highest of the other named amine catalysts. For use as co-catalysts in the system with secondary imidazoles to develop the required exotherm for initiating catalyst activity o'L the secondary imidazole, there come into consideration only those catalysts of high activity at room temperatare which exhibit rapid development of an exothermic rise in temperature of the reaction rnixture, at least in the ma,-nitude of 0.1' F./sec., of which the tin compounds and 1,4-diazabicyclo(2.2.2)-oc,ane are representative. The effect of temperature in activating secondary imidazole catalysts for the polyurethane catalysis will b-. appreciated from a comparison of the curves plotted in FIGURES 1 and 2, wherein these are compared with diazabicyclo octane at 25' C. and at 75-80' C., respectively, on the basis of viscosity change with time using as the model system 150 gm. of polypropylene glycol of 2000 moleclle wei.-ht and 0.15 gm. of catalyst, ten milliliters of tolylene diisocyanate (TD 80) being added to the mixture. It wifl be observed in FIGURE 1 that at room temperature, the secondary imidazoles as a rule showed very little activity as compared to diazabicyclo octane (about -1/20 of that of diazabicyclo octane) while the tert@'ary imidazole has an activity of about 40% of that of diazab@' cyclo octane. At the higher temperature (FIGURE 2) the secondary imidazoles showed appreciable
[7]13 activity amounting to 23-57% of that of the diazabicyclo octane. By plotting the time/viscosity curves of FIGURE 1, relative reaction rates were determined from the initial slopes of the several cur-ves at 25' C. Taking the rate for diazabicyclo octane (r@1) as unity, the comparalive rate,s for the other catalysts are given in Table 2 below. From the time/viscosity curves of FIGURE 2 (at 7580' C.) similarly r values were determined and related to the r value for diazabicy-,Io octane, also tabulat@-d in Table 2. The ternperature sensitivity of each catalyst compared to that of diazabicyclo octane will be seen from columns 3 and 4 of the table. TABLE 2 1 2 3 4 r25 r75 r75 Percent r- activa25 tion - Di,,izabicyclo octane ---------------------- 1.0 1.0 1.0 0 2-etliyl-4-metliyl imidazole --------------- 0.05 0.37 7.0 700 I3niclazole -------------------------------- 0.08 0. 23 3.0 300 2-etliyl-imidazole ------------------------- 0.09 0.40 3.3 330 2,4-dimethyl iraidazole ------------------- 0.09 0.58 6.0 600 2-metliyl iiridazole ----------------------- 0.12 0. 55 4. 5 450 2,4,5-trimethyl iinidazole ----------------- 0.50 1.49 3.0 300 This un@qtie temperature sensitivity of the secondary imidazoles can be used to particular advantage in several ways: (1) In polyurethane moldin.- cor@ipositions where appreciable "pot life" is desired; for example, v;here a molding composition is rnade up and a period of from one to 16 or more hours is needed to prepare and cast the molds. During the interval the condensation reaction is very slow at room temperature, but when the prepared mix incli-icling secondary imidazole as catalyst is poured into.the warnied mold or the mixture warmed before pouring, the cast mix reacts rapidly to form the desired condensation product. (2) In thermosetting cements the polyurethane adhesive mix including the dormant catalyst may be placed on the pieces to be joined, affording the operator time to locate and clamp these pieces in position. The set-up can then be heated, for example, by conveying through an oven, wherein the joined parts are sealed by heatin-. luustrative examples of certain of these appjications of the secondary imidazole catalyst in non-c-.Ilular polyurethane,s appear below: Example XIV An adhesive composition having good shelf life is made up from the followingParts by wt. Polyethylene glycol (M.W. 375-400) ----------- 400 Tolylene diisocyanate - ------------------------ 350 Imidazole ------------ ----------------------- 2 Organo-silicone (DC 199)1 -------------------- 1 Benzene -------------- ----------------------- 110 1 Hydrophobic alkylene-oxide silicoiae polymer. The polyether -Iycol is added to the diisocyanate dissolved in benzene. The imidazole and silicone were then added and tne solution allowed to precure by autogenous reaction. A viscous amber liquid results wh;ch is stable up to 12 months at 50' C. if kept free of water. The viscous precured adduct is mixed with the imidazole dissolved in benzene. Shelf life remains -,ood for a month or more at ambient temperatures and up to 12 months at moderately low temperatures, e.g., 5' C. Th.- stable adhesive adduct is applied in a thin coating on the materials to be cemented, e.g., steel to glass. No further reactive cure is required other than volatilization of the solvent present. When the adhesive coated surfaces are tacky (in rou,-hly 10 to 20 minutes) the pieces are pressed into contact and passed tbrough heated (80-100' C.) rors or held in a heated (100' C.) press for approxi3,152,094 14 mately 2 minutes to set and finally cure the adhesive. Bond strength is good immediately on lea-ving the press, however, full bond stren.-th is developed on cooling. Glass bonded to steel in 'Lhis example had tensile strengths of 800 to 1000 p.s.i., or an avera,-e bond stren.-th of 900 p.s.i. This thermosetting adhesive is applicable wherever the work pieces are stable at temperatures of 100-120' C., for example, vulcanized rubber to steel, aluminum sheet to methyl methaerylate, etc. 10 Example XV A modification of the above method permits a new tecbniqil-e of dry bonding. The above forniulation is prepared usin-, only 10 gm. of benzene to dissolve the 15 or-.ano-silicone. The resultant precured viscous liquid is mixed with the imidazole catalyst in benzene solution, cast and dried to a workable plastic sheet. Coupons of the dry adhesive, cut to size, are placed between the work pieces to be cemented and the sandwich, in this instance 20 aluminum foil 0.001" in thickness, adhesiv.- ffim 0.001" and cellulose acetate sheet 0.001" are laminated, pressed througb collandering roils heated to 80' C. and cemented to a tough laminate in a press time of one mh-iute at 150 pounds pressure. This aluminum-urethane-acetate sheet 25 bas a tensile strength of over 1500 p.s.i. THE RMOSETTD4G COATING COMPOSITIONS Coatin g compositions are of particular value on paper, textile s, leather or metals. Esp.-cially in wire coatings @- 0 polyur ethane coat;ngs exhibit highly desired gloss, water and solvent resistance, -xcellent electrical resistance, low gas permeability and high vieather resistance. Because of the high reactivity of the polyol materiais with isocyanates, it is custor@iary to react the polyol, such as castor oil, 3a with a portion of the diisocyanate up to the molar equivalent, thus to form a prepolymer to which the catalyst is added. The polymer-catalyst mixture has excellent storage stability with secondary imidazoles as catalysts, as seen from the example below. 40 Exam ple XYI (a) Parts by weight 45 Castor oil ----------------------------------- 380 Diphenyl methane diisocyanate ----------------- 380 These two ingredients are stirred and heated by autogenic condensation to approximately 85' C. and further cooked for two hours at temperatures up to 140' C. The 50 obtained prepolymer is allowed to cool and then there is added thereo with agitation (b) Parts by wt. 55 2,4-dimethyl imidazo'@e ---------------------- 3.8 Organo-silicone (DC 199) ------------------- 0.4 dissolved in D:,Phenyl methane diisocyanate ---------------- 200.0 60 The riixed catalyzed resin is storable at ordinary temperatures for months. In preparing coatings on wire, the wire is cleaned, dried and dipp.-d successively in (a) organic isocyanate solution, (b) liquid resin prepolyner and passed through curin.a ovens at 80 to 110' C. for a 65 reaction and etiring tiine of about 3 minutes. Longer heating alid curing times are permitted; however, closely adherent, dense coatings are produced in the lesser (3 min.) oven tiine. Metal and plywood panels are similarly coated by 70 dipping the clean dried piece into th6 polymer resin bath, then being conveyed mechanically through infrared heated ovens to obtain temperature activation of the catalyst at 80+' C. and final <)ven curing of the urethane coating at 125' C. for 20 minutes to one hour for maximum 75 hardness.
[8]STORAGE STABLE POTRING COMPOUNDS The process of potting or encapsulating mechanical items, such as electrical or electronic comi)onents, has come into wide use in this rapidly growing industry. The advantages of such weither-proof, scratchproof 5 packaging is obvious, but the necessity of havin-. tough coating materials to feed a manufacturer's assembly line requires compositions having low surface tension at ordinary temperatures to Jay down a thin, smooth coating on contact and a stable composition that does not harden 10 in air at ordinary temperatures, but condenses and hardens rapidly at moderately elevated te, -nperatures. A pottin.@ compos@tion that produces tough, flexible encapsulation essentially free of gas bubbles is illustrated in the following example. 15 Example XVII Parts by wt. Castor oil ----------------------------------- 760 TDI --------------------------------------- 640 20 Hexylene glycol ------------------------------ 120 2-ethyl imidazole ----------------------------- 5.6 Silicone oil ---------------------------------- 7.5 The dried castor oil, TDI and glycol are mixed, with the secondary imidazole catalyst and silicone oil added -5 and dissolved. The potting solution is fed througn closed lines to a dippiig pot where the conveyed mechanical goods are dipped, drained and rotated (to form an even non-dripping coat) as the article is conveyed to a heaidrying and preferably vacuum oven. Th,- piece is heated rapidly to a minimum of 80' C. and held at this temperature approximately two minutes. To insure thinner, bubble-free enclosure the ovens are preferably heated by infrared lamps and for at least the iirst half of the oven travel time the conveyed parts move through a vacuL)M 015 chamber to insure good de-asification of the coating. The condensed and cured film is allowed to cool and the coated article packed in appropriate containers. The specific advantage of pottin.- compositions employing thermally-activated secondary imidazole catalyst @10 will be seen from the following comparison: Example XYIII Parts by wt. Tolylene diisocyanate ------------------------- 300 45 Castor oil (dry) ------------------------------ 375 Organo-silicone oil --------------------------- 5 These components are mixed at room temperature and then heated gradually with agitation to 70' C. for not more than two hours to build up a prepolymer of about 50 40,000 centipoises at room temperature. The product is evacuated to <10 mm. Hg to remove gas bubbles. The vacuum is relieved with dry gas (nitro,-en) and the prepolymer cooled to room temperature. This prepolymer mix is used in the following cases: 55 A. To a sample of the above prepolymer there is added 6 gm. of Quadrol (tetrakis-2-hydroxypropyl ethylene diamine) and the coniposition r)oured in a mold and placed in an oven to cure at 100' @-'. To obtain a good tough product about 18 to 20 hours are required for the cure. 60 B. To another sample of the above prepolymer th@-re is added in addi' ion to the Quadrol, 5 gm. of diazabicyclo octane. Because 6f the rapid catalysis of the cross-linking reaction there is produced an inimediate stringy composition which adheres to the pot (with high material r)5 loss) and pours unevenly into tho mold. Curing under these conditdns is quite rapid with autogenous heat building up to 125' C. or more in a half-hour. The prbduct is une-ven in texture, not well adhered to the mold, and is overheated in thick segments to produce a 7o dark bubbled product. C. To a third sample of the above polymer there is added with the Quadrol 6 gm. of 2,4-dimethyl imidazole at room temperalure. The composition is poured into a heated mold and the mold plus contents put under vaeu75 um (10 mm Hg) to dd@asify the mix. At temperatures of about 70. F. the condensation and cross-linking take place rapidly. The product is condensed and cured to a tough finely molded product in 60 to 80 minutes without further heating. The catalytic effect of secondary imidazoles in polyurethane rubber formulations is seen from the following illustration: Erample XIX Parts by wt. Adiprene LI -------------------------------- 100 LG 56 -------------------------------------- 85 2@methyl imidazole --------------------------- 0.5 'Prepolymer of tolylene diisocyanate and polytetramethylene glycol (ill.W. 2000) ; see SPE Journal, April 1959, p. 298. The catalyst was added to the polyol and heated with stirring to dissolve the material. The solution was cooled to room temperature, the Adiprene added, and the resulting mixture stirred for five rainutes. The experiment was repeated at room temperature and at 100' C. In the room temperature run about 23 hours were required for the mixture to set to tarky consistency and about 44 hours to dry state, as compared with diazabicyclooetane as a control Nvhich set in about 2 hours to tacky state and 7.4 hours to dry state. At 100' C. 2-methyl imidazole set dry in about 48 minutes as compared to about 27 minutes for the diazabicyclooetane. A run made with 2-ethyl 4-methyl imidazole (reqil-iring almost 80 hours at room temperature to set dry), when mixed at 100' C. set dry in 36 minutes. The secondary short chain trialkyl imidazoles (methyl through butyl substituents) while having a room teniperature activity in condensation and polymerization reactions (as measured by the desoribed polypropylene glycoltolylene diisocyanate model system) of one-third to onefourth that of dia zabicyclooctane, at higher temperatures (75-85' C.), the activity of the trialkyl imidazole approaches or exceeds that of diazabicyclooctane. The following example is illustrative of a mixed catalyst system employing a fastacting co-catalyst in association with a secondary irnidazole, in a "one-shot" elastomer: Example XX Parts by wt. Polypropyleneglycol (M.W. 1000) -------------- 100 2-methyl-tetrahydrobenziinidazole -------------- 0.4 N-phenyl-diethanolamine ---------------------- 13.6 Stannous octoate ----- ------------------------ 0.2 Tolylene diisocyanate(80:20) ----------------- 30.3 The stannous octoate and the allcyl tetrahydrobenziniidazole compound were dissolved in the molten diethanolamine and the obtained solution niixed with the polypropylene glycol. The mixture was carefully degassed undi-r vacuum (3 mm. H@ pressure) at 80-100. C. f . or twenty to forty minutes. . The diisocyanate was then added to the degassed resin mixture and poured inlo a mold, then again briefly degassed under vacuum (50 mm. Hg. pressure) and retumed to atmospheric pressure. Th@- molded product was cured in the mold at 140' C. for two hours, then released. The cured product released from the mold was of rubberycharacteristics, stretchina slowly with full recovery. By using the slow-acting @secondary imidazole compound, there is ample time delay to permit thorough mixing and d.-gassing prior to and during molding, thereby avoiding or minimizing gas bubbles in the product. The preparation of 2-methyl tetrahydrobenzimidazole by hydrogenation of 2-methyl benzimidazole is described in Helvetica Chemica Acta (1938), vol. 21, at p. 1693. Obviously many modifications and variations of the - invent-ion as hereinbefore set forth may be made without departing from the spirit and scope thereof, and
[9]3,152,094 17 therefore only such lin-iitations should be imposed as are indicated in the appended claims. VVhat is
