3,756,992 United States Patent Office Patented Sept. 4, 1973 1. 2 urethanes in water without the use of solvents. Thus for 3,756,992 example an ionic polypropylene glycol polyurethane which POLYURETHANE POLYELECTROLYTES AND has been modified with isocyanate groups in the terminal PROCESS FOR PREPARING SAME Dieter Dieterich, Leverkusen, Germany, assignor to Bayer positions can be injected in the form of a hot liquid into Aktiengesellschaft, Leverkusen, Germany Water or distributed in water by means of mechanical No Drawing. Continuation of abandoned application Ser. stirrers which produce high shearing forces. Dispersions No. 809,987, Mar. 24, 1969. This application Mar. 13, of high molecular weight polyurethanes can also be ob 1972, Ser. No. 234,315 tained in this way by reacting the emulsion droplets with Claims priority, application Germany, Mar. 27, 1968, the water. P 17 70 068.4 0. This procedure is, however, technically complicated and Int, CI. C08g 22/04 difficult to reproduce. Furthermore, it is in practice limited U.S. C. 260-77.5 Q 16 Claims to polyether polyurethanes of low viscosity. It is also known that polyurethanes which are dispersed or dissolved in water may be cross-linked by means of ABSTRACT OF THE DISCLOSURE 15 formaldehyde (German Pat. No. 1,187,012). In such a Polyurethanes are prepared by dispersing solid or liquid case, formaldehyde, compounds which give off formalde polyurethane polyelectrolytes containing methylol groups hyde or compounds which react like formaldehyde, are by mixing with water, subjecting the electrolytes to a heat added to the polyurethane dispersion in the course of its treatment of 25 to 200° C. and removing the water. preparation and then react with the polyurethane in a 20 cross-linking reaction during the subsequent drying. The addition of aqueous solutions of formaldehyde during the This is a continuation of application Ser. No. 809,987, synthesis of the polyurethane mass in the presence of free filed Mar. 24, 1969, and now abandoned. NCO groups is, of course, out of the question, since the This invention relates to polyurethane plastics and a water would immediately react with the free NCO groups, method of production. More particularly, it relates to an 25 which would lead to the formation of a gelled mass. improved process for preparing new aqueous polyurethane It may, therefore, be said that polyurethane dispersions dispersions. having good technological properties could hitherto only Numerous processes are already known for the prepara be produced, in practice, by using organic solvents. If tion of polyurethane resins from aqueous polyurethane one wishes to emulsify prepolymers containing free NCO dispersions. 30 groups with the use of emulsifiers it is advantageous to For example, prepolymers with terminal reactive iso use hydrocarbons which are left in the latex. In the case cyanate groups obtained by reacting compounds which of dispersions of polyurethane polyelectrolytes, the low have active hydrogen atoms with a stoichiometric excess boiling solvent used for the preparation of the dispersion of diisocyanates may be dissolved in an organic solvent is removed from the dispersion by distillation and re and emulsified with the aid of emulsifiers under the action 35 turned to the cycle. Although the dispersions are com of powerful shearing forces in water or in solutions of pletely free from organic solvents when applied, this meth diamines in water (German Auslegeschrift No. 1,097 od of preparation is economically less satisfactory. 678) (U.S. 2,968,575, Mallonee). In this process, an emul It is therefore an object of this invention to provide sion of the reactive prepolymer is first produced. A chain improved polyurethane polymers. It is another object to lengthening reaction then takes place as a result of the dif 40 provide improved polyurethane dispersions. It is another fusion of water or diamine into the droplets of the emul object to provide aqueous polyurethane dispersions with sion and reaction with the isocyanate groups occurs so out the necessity of using solvents. It is still another ob that, finally, dispersed particles of polymeric polyurethane ject of this invention to provide polyurethane polymers ureas are formed. This process has the disadvantage that from dispersions that are useful in all types of applica it is difficult to influence and control the chain lengthening 45 tions. reaction because it takes place in the droplets of emulsion The foregoing objects and others which will become ap and, as is well known, the chain lengthening reaction of parent from the following description are accomplished polyisocyanates with water or diamines proceeds with in accordance with this invention, generally speaking, by considerable chain branching. In addition, the dispersions providing polyurethanes by dispersing methylol-contain obtained are not stable for any length of time. 50 ing, solid or liquid, relatively low molecular weight poly These disadvantages can be partly avoided by a con urethane polyelectrolytes in water and then effecting fur tinuous method of preparation in which the emulsification ther chain lengthening. This can be done by heat treat of the prepolymer is carried out at a low temperature ment, before and/or during and/or after removal of the and the diamine is added subsequently. Even by this varia water via methylene bridges. According to a particular tion of the process, however, relatively coarse dispersions 55 embodiment of the process, the polyurethanes to be dis which tend to sediment out or coagulate are obtained, and persed contain reactive terminal groups which are partic the resulting coatings, films and impregnations have very , ularly reactive with formaldehyde. These groups are re little resistance to water. It has not so far been possible acted with formaldehyde in the presence of water during to produce, by such a process, latices with particles be or immediately before dispersion. According to another low 400 mu, which would dry at room temperature or, at 60 embodiment of the process, the polyurethanes which are least, at temperatures below 80° C. to form coatings with to be dispersed are reacted, e.g., via isocyanate groups, satisfactory properties rendering them useful. In addition, with compounds which contain reactive methylol groups, coarsely disperse, sedimenting but redispersible dispersions so that polyurethanes with terminal free methylol groups cannot be produced by this process. are formed. Contrary to expectations, premature cross Furthermore, numerous processes are known for pro 65 linking does not occur; on the contrary, the process of ducing emulsifier-free polyurethane dispersions by incor dispersion is considerably facilitated by the addition of porating cationic or anionic salt groups into the polyure formaldehyde and the terminal methylol groups. Chain thane polymer chains and mixing solutions of such poly lengthening to produce the high molecular weight poly urethanes in organic solvents with water. Stable aqueous urethane thus takes place during and after the dispersion. polyurethane dispersions are obtained after removal of 70 A person skilled in the art would not have expected the organic solvent by distillation. that the preparation of aqueous polyurethane dispersions, It has also been proposed to disperse such ionic poly in other words a colloidal two-phase system would be 3,756,992 3 4. possible according to the invention without the aid of (1) has an average molecular weight of less than about (1) emulsifiers, (2) dispersing apparatuses such as high 25,000, preferably about 2,000 to about 10,000, speed stirrers or other apparatuses which produce shear (2) contains hydrophobic nonionic chain segments of at ing forces, (3) solvents, since, according to the state of least 60 chain links, the art, at least one of these aids is necessary, and that (3) contains 4 to 120 millieduivalents percent, preferably one can obtain, e.g., hydrophobic coatings from the re 8 to 80 milliequivalents percent of salt groups or of sulting dispersions. groups which are capable of salt formation which are This invention thus relates to a process for the prepara converted into salt groups in the course of the process, tion of polyurethanes which is characterized in that solid (4) has a viscosity of less than 1,500 poises and pref or liquid polyurethane polyelectrolytes which contain O erably 50 to 1,000 poises at 120° C. and methylol groups are dispersed by mixing them with water, (5) contains terminal acylated amino groups of the gen and the dispersed poyurethane polyelectrolytes are Sub eral formula jected to heat treatment at 25 to 200° C. before and/or -X-NHR during and/or after removal of the water. According to the invention, higher molecular weight which are reactive with formaldehyde, polyurethane polyelectrolytes are preferably used. By in which formula: "polyurethane polyelectrolytes' is meant compounds hav X represents -CO-, -CS-, -SO2-, ing terminal reactive methylol groups and which have been obtained from higher molecular weight polyiso -NR-CO cyanates and methylol compounds, and which have: -NR-CS-, -O-CO-, -S-CO-, -O-CS-, -O-SO-, -CNR-, -NR-CNR-, (1) an average molecular weight of less than about -CO-NR-CO 25,000, preferably about 2,000 to about 10,000, (2) hydrophobic nonionic chain segments of at least 60 -CS-NR-CS chain links, (3) 4 to 120 millieauivalents percent, preferably 8 to 80 millieduivalents of salt groups or of groups which are capable of salt formation and which are converted into salt groups in the course of the process, and (4) a viscosity of less than about 1,500 and preferably 30 'i about 100 to about 1,000 poises at 120° C. The polyurethane electrolyte is dispersed with water at to ?il, about 20 to about 150° C., preferably at about 50 to about 130 C, the quantity of water being from about and 0.5 to about 4 times the quantity of polyurethane poly Z represents electrolyte.