A PROCESS FOR PREPARING A POLYOXAZOLIDONE

Abstract: A process by which a polyepoxide and a polyisocyanate are reacted to form a polyoxazolidone. The process is characterized by conducting said reaction in the presence of a catalytic amount of an organoantimony iodide catalyst. In this process, the oxazolidone forming reaction proceeds much more rapidly than the trimerization reaction of the polyisocyanate or the homopolymerization of the polyepoxide. As a result, the product polymer or polymer precursor contains a surprisingly small proportion of isocyanurates. In addition, the overall rate of reaction is substantially increased as compared to that achieved with conventional catalysts, thereby reducing the time and stringency of conditions required to form the desired product.

Description: A PROCESS FOR PREPARING A POLYOXAZOLIDONE This invention relates to a process for preparing a polyoxazolidone. More particularly, this invention relates to a process for preparing polyoxazo¬ lidone containing relatively small proportions of trimer- ized polyisocyanates. It is well known to react an epoxide with an isocyanate to form an oxazolidone. Such reactions are generally carried out in the presence of a catalyst. Typical catalysts for this reaction include lithium bromide, quaternary ammonium salts, tertiary amines, Lewis acids, such as aluminum chloride, complexes of these Lewis acids with a Lewis base, and similar materials. In similar manner, polyoxazolidones can be prepared by reacting a diepoxide (i.e. a compound having at least two oxirane groups) with a polyiso- cyanate (i.e. a compound having at least two isocyanate groups). However, whereas the reaction of a mono- epoxide and a monoisocyanate to form an oxazolidone proceeds relatively cleanly and in good yield, the corresponding reaction between higher functionality 5 epoxides and isocyanates results in the formation of substantial quantities of undesirable by-products. The major by-products are polyethers prepared by the homo- polymerization of the polyepoxide and isocyanurates formed by the trimerization of the polyisocyanate. Of 10 these, the trimerization reaction is particularly disadvantageous since the trimerization leads to the formation of very high functionality materials which give rise to very highly crosslinked, brittle polymers. Unfortunately, the catalysts conventionally used in 15 preparing polyoxazolidones do not selectively catalyze the oxazolidone reaction, and substantial quantities of isocyanurates are formed. Generally, the polyoxazoli- done prepared by processes known in the art contains from 20 to 40 mole percent or more of isocyanurates. 20 For this reason, it would be desirable to provide a process whereby a polyepoxide and polyiso¬ cyanate are reacted to form a polyoxazolidone contain¬ ing relatively small quantities of trimerized isocy¬ anates. 25 This invention is directed to a process for preparing a polyoxazolidone by reacting together a polyepoxide and a polyisocyanate. The process is characterized by reacting said polyepoxide and poly¬ isocyanate in the presence of a catalytic amount of an 30 organoantimony iodide. In this process, the oxazolidone- -forming reaction proceeds much more rapidly than the trimerization reaction of the polyisocyanate or the homopolymerization of the polyepoxide. As a result, the product polymer or polymer precursor contains a surprisingly small proportion of isocyanurates. In addition, the overall rate of reaction is substan¬ tially increased as compared to that achieved with conventional catalysts, thereby reducing the time and ■ stringency of conditions required to form the desired product. In this invention preferred catalysts are as represented by the structure R χ SbI y wherein x and y are each numbers from 1 to 4, provided that the sum of x + y is equal to or less than 7, each R is independently an aliphatic, cycloaliphatic, aromatic, alkyl or aralkyl group which optionally may contain hetero atoms or other substituent groups which are inert to the reaction of the polyepoxide and the polyisocyanate to form a polyoxazolidone polymer or polymer precursor. In the case of a polymer precursor, the substituent group is also advantageously inert to the reaction thereof to form a polymer. Suitable substituent groups include, for example, aryl-bonded halogen and alkoxy. More preferably, the antimony is pentavalent, i.e. the oxidation state of the antimony atom is +5, and in the formula x is 3 and y is 2 or 4. These are triorganoantimony di- or tetraiodides. Preferred as the R groups are aromatic groups having from 6 to 12 carbon atoms such as, for example, phenyl, tolyl, naphthyl, and o-, m- or p- halo-benzyl; alkyl groups such as, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl and other alkyl groups having from 4 to 12 carbon atoms as well as alkoxylated or halogenated derivatives thereof; and benzyl and inertly substituted benzyl groups. The preferred di- and tetraiodide catalysts are substantially equivalent in their activity and selectivity in the oxazolidone forming reaction. However, the tetraiodide is more preferred in making isocyanate-terminated polyoxazolidone polymer precur- sors because the products of the diiodide-catalyzed reaction tend to form small quantities of isocyanurates upon standing. The tetraiodide-catalyzed isocyanate terminated reaction products are significantly more stable. Exemplary antimony catalysts useful herein include trimethy1antimony diiodide, trimethylantimony tetraiodide, triethylantimony diiodide, triethylanti- mony tetraiiodide, triisopropylantimony diiodide, triisopropyl- antimony tetraiiodide, methyldiethyl- antimony diiodide methyldiethylantimony tetraiodide, tri-n-butylantimony diiodide, tri-n-butylantimony tetradiiodide, triphenylantimony diiodide, triphenyl- antimony tetradiiodide, tribenzylantimony diiodide, tribenzylantimony tetraiiodide, and tri-n-hexylantimony di- or tetraiiodide. The preferred antimony catalyst is advan¬ tageously employed in relatively small amounts in the reaction. Preferably from 0.3 to 20, more preferably from 1 to 5, and most preferably from 2 to 4 moles of the antimony catalyst are employed in the reaction per 100 mole of the polyepoxide. Use of the catalyst in the preferred and more preferred ranges provides for minimal isocyanurate formation without using unnecessary amounts of catalyst. The antimony catalyst is readily prepared by reacting the corresponding organoantimony compound, such as R_Sb, with iodine ( I ~ ) . When equimolar quan¬ tities thereof are employed, the diiodide is formed. Addition of a second mole of iodine forms the tetra- iodide. Generally, the reaction of the iodide and the organoantimony compound is conducted in a solvent. Polyepoxides and polyisocyanates are suitable such solvents. The reaction of the organoantimony compound with iodine proceeds readily at ambient or elevated temperature. This reaction proceeds particularly well at the conditions of the polymerization of the poly¬ epoxide and the polyisocyanate. Accordingly, it is possible, and generally preferable, to prepare the antimony catalyst in situ by charging the organoanti- mony compound and iodine to the polymerization vessel and carrying out the polymerization reaction and the catalyst-forming reaction simultaneously. The organo¬ antimony compound used as a starting material is readily formed in the reaction of the corresponding organo ag- nesium halide and antimony trichloride or tribromide. The polyepoxide used in this invention con¬ tains a plurality of epoxy, i.e. ,β-oxirane groups. Although said polyepoxide can have as many as 100 or more epoxy groups, it is highly preferred that the functionality of the polyepoxide be relatively low, i.e. from 2 to 10, more preferably from 2 to 4, and most preferably from 2 to 3. Lower functionalities are preferred because they give rise to less highly cross- -linked polymers, which tend to have better physical and thermal properties as well as being more easily processed. Diepoxides give rise to linear, thermoplastic polymers when reacted with a diisocyanate. Among the polyepoxides usefully employed herein are those represented by the general structure wherein X is the residue of an active hydrogen- -containing moiety after removal of said active hydrogen, R 1 is an organic polyradical and n is at least 2. N is preferably from 2 to 4, more preferably 2 to 3. Such polyepoxides are advantageously prepared by reacting a compound having a plurality of groups containing active hydrogen atoms with a halogen-containing oxirane such as epichlorohydrin or epibromohydrin. In structure I, the group X is advantageously R 2 0 0 R 2 0 0 I II It I II II -0-, -NH-, -N-, -C-, -0-C-, -S-, -N-C-, -O-C-NH- or a similar group, wherein R 2 is inertly substituted lower alkyl or phenyl. Preferably, "the group X is -0- and the polyepoxide is one prepared in the reaction of a polyhydroxyl containing compound with a halogenated oxirane as discussed hereinbefore. Exemplary polyepoxides include epoxy-terminated derivatives of bisphenols, such as are represented by the structure wherein each A is independently a lower alkylene group such as, for example, methylene, ethylene, or isopro- pylidine O II or -0-, -S-, or -C-; each B is as defined by A, and/or -OCH 2 CHOHCH 2 0-, each R is independently hydrogen, halogen or lower alkyl, and m is a number from 0 to 30, preferably from 0 to 10 and more preferably from 0.1 to 3. In addition, derivatives of the materials represented by structure II in which one or more of the positions on the group A is substituted with an inert substitutent such as, for example, halogen, aryl, and alkyl are also useful herein. Suitable such epoxides include the commercially available resinous reaction products of an epihalohydrin with the the diverse bisphenols and halogenated bisphenols, particularly the reaction products of an epihalohydrin with bisphenol A or bisphenol F or halogenated derivatives thereof. These resins preferably have an average epoxide equi¬ valent weight from 155 to 2000. Suitable such epoxy resins include those sold commercially as DER* 317, DER 330, DER 331, DER 332, DER 333, DER 337, DER 642U, DER ''Trademark of The Dow Chemical Company. 661, DER 662, DER 663U, DER 664, DER 664U, DER 667, DER 673MF, DER 542, DER 511-A80, DER 521-A75, and DER 599 epoxy resins, all available from The Dow Chemical Company. Also suitable are the corresponding aromatic glycidyl amine resins wherein the various ether linkages are replaced by -NH- groups. Also useful herein are the so called poly- nuclear phenol glycidyl ether derived resins. Also suitable are the so-called epoxy phenol novolac resins and epoxy cresol novolac resins which can be represented by the structure I wherein n is a number from 0 to 20 and each R 3 is independently hydrogen, halogen, lower alkyl, aryl or aralkyl. Halogenated derivatives of such resins are also useful herein. In addition, epoxy resins prepared by reacting an organic diene with an aromatic hydroxyl-containing compound and subsequently reacting the resulting product with an epihalohydrin, as are described in U.S. Patent 4,390,680 to Nelson. Suitable aliphatic epoxy resins include the hydrogenated derivatives of the foregoing aromatic epoxy resins, as well as those in which the group R 1 of Structure I is lower alkylene, especially ethylene and isopropylene, a dialkylene ether or a polyoxyalkylene group. Such resins are advantageously prepared by reacting an alkylene glycol or polyether polyol with an epihalohydrin. Examples of such resins include DER 732 and DER 736, both of which are available from The Dow Chemical Company. Also useful are aliphatic epoxy resins pre¬ pared in reaction of cycloolefins with peracetic acid, as well as diglycidyl ethers of cyclic dicarboxylic acids. The foregoing polyepoxide is reacted with a polyisocyanate in the presence of the aforedescribed antimony catalyst to form a polyoxazolidone. The polyisocyanate may be highly functional but preferably has the functionality of less than 10, preferably from 2 to 4, and more preferably from 2 to 3. Organic polyisocyanates which may be employed include aromatic, aliphatic and cycloaliphatic poly- isocyanates and combinations thereof. Representative of these types are diisocyanates such as m-phenylene diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,- 6-diisocyanate, xylenediisocyanate, tetramethylxylene diisocyanate, isophorone diisocyanate, hydrogenated diphenyl methane diisocyanate, hydrogenated xylene diisocyanate, hexamethylene-l,6-diisocyanate, cyclo- hexane-1,4-diisocyanate, hexahydrotolylene diisocyanate (and isomers), naphthalene-l,5-diisocyanate, 1-methoxy- phenyl-2,4-diisocyanate, diphenylmethane-4,4'-diiso- cyanate, 4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,- 4'-biphenyl diisocyanate, and 3,3'-dimethyl-4,4'-diphenyl diisocyanate, the triisocyanates such as trifunctional polymethylene polyphenylisocyanates and tolylene-2,4,- 6-triisocyanate; and tetraisocyanates such as 4,4'-di- methyldiphenylmethane-2,2' ,5,5'-tetraisocyanate. A crude polyisocyanate may also be used in the practice of the present invention, such as the crude toluene diisocyanate obtained by the phosgenation of a mixture of toluene diamines or the crude diphenyl- methylene diisocyanate obtained by the phosgenation of crude diphenylmeth lenediamine. The preferred undis- tilled or crude isocyanates are disclosed in U.S. Patent No. 3,215,652. Alternatively, an isocyanate-terminated prepolymer or quasi-prepolymer prepared by reacting an excess of a polyisocyanate with a polyol of low or high equivalent weight may be employed as the polyisocyanate herein. The relative proportions of the polyepoxide and polyisocyanate employed control to a large extent the characteristics of the product polyoxazolidone. By using a stoichiometric excess of the polyisocyanate, an isocyanate-terminated polyoxazolidone polymer is prepared. Similarly, the use of an excess of the polyepoxide leads to the formation of epoxide terminated polymers. The use of excess amounts of the polyepoxide or poly¬ isocyanate can also be used to control the molecular weight of the polymer, since larger excesses of either component tend to produce lower molecular weight polymers. Using substantially equivalent amounts of the polyepoxide and polyisocyanate provides a process where higher molecular weight polyoxazolidones can be formed. Thus, the relative amounts of polyepoxide and polyisocyanate employed may vary over a relatively wide range, such as for example 10:1 to 1:10, on a molar basis. The oxazolidone-forming reaction is advan¬ tageously carried out by heating together the poly¬ isocyanate and polyepoxide in the presence of the antimony catalyst described herein. Advantageously, the reaction temperature is from 80 to 180°C. The optimum reaction temperature depends somewhat on the particular polyisocyanate employed. Aromatic poly- isocyanates which trimerize relatively slowly, such as diiphenylmethane diisocyanate are preferably reacted at a temperature from 80 to 120°C. Those such as toluene- diisocyanate which more rapidly trimerize are preferably reacted at a temperature from 120 to 175°C. Aliphatic polyisocyanates are also preferably reacted at a temper¬ ature from 120 to 175°C. It has been found that the use of significantly higher or significantly lower temperatures than described in this paragraph tends to promote the formation of higher amounts of isocyanurate groups. It will also be apparent that changes in temperature and amount of catalyst will effect the rates of the reaction. Under the conditions of tem- perature and amount of catalyst described herein, the reaction is typically completed in from 5 minutes to 8 hours, and more typically from 5 minutes to 4 hours. The oxazolidone forming reaction is generally carried out neat, but may if desired be carried out in the presence of a suitable diluent or solvent for the reactants. Ketones, aromatic hydrocarbons or other solvents which are inert to the polymerization reaction are suitable. Solvents which only weakly or negligibly coordinate with the catalyst are preferred since they tend to inhibit the oxazolidone forming reaction. The reaction can be run batch-wise or continuously, as in a coil reactor. Isocyanate-terminated oxazolidone polymer precursors prepared according to this invention can be reacted with a polyol, polyamine or other material containing a plurality of active hydogen atoms to form a polyurethane or polyurea. Generally speaking, the isocyanate-terminated oxazolidone polymer precursor is used in the same manner as conventional polyisocyanates to prepare a polyurethane. The use of the oxazolidone polymer or precursor does not generally require any special processing conditions, and any of the conven¬ tional techniques for preparing polyurethanes are suitably used. In particular, polyurethane films, elastomers, structural foams, rigid foams, flexible foams all can be prepared with the oxazolidone polymer or precursor prepared by the process of this invention. Techniques for preparing polyurethane polymers which may be employed in conjunction with the isocyanate- -terminated oxazolidone polymer precursor include, for example, those described in U.S. patent numbers 3,821,130, 3,888,803, 4,280,007, 4,294,934 and 4,374,210. Similarly, the epoxy terminated oxazolidone polymer precursor can be reacted in conventional manner with epoxy curing agents to form epoxy coatings, resins, and adhesives. Epoxy curing agents include diamines and other compounds containing two or more groups which react with epoxy groups to form a bond thereto. Exem¬ plary epoxy curing agents and methods for preparing cured epoxy resins are described, for example, in Lee and Neville, Handbook of Epoxy Resins, McGraw-Hill Book Co., New York (1967). Those polyurethane polymers and cured epoxy resins prepared using the oxazolidone polymer or pre¬ cursor in this invention exhibit excellent thermal properties. In addition, such polymers exhibit good chemical and solvent stability. Further, these polymers have generally good impact properties as compared to conventional oxazolidones polymers. In preparing polyurethanes or cured epoxy resins according to this invention additives such as, for example, fillers, fibers, antioxidants, internal mold release agents, pigments, surfactants, catalysts, and blowing agents can all be employed in conventional manner. The following examples are provided to illus- trate the invention but not to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated. Examples 1 and 2 In a suitable flask are charged 6.6 grams of a 174 equivalent weight bisphenol A/epichlorhydrin epoxy resin, 15.4 grams of toluenediisocyanate, 0.27 grams (0.76 mmol) triphenyl antimony and 0.39 grams (1.54 mmol) of iodine. With stirring, the mixture is heated to 150°C and held at this temperature for 10 minutes. The reaction mixture is then cooled and analyzed by infrared spectroscopy and gel permeation chromatography. These tests indicate the formation of oxazolidone rings, the complete disappearance of the epoxide groups and the substantial absence of isocy- anurate groups. Nuclear magnetic resonance spectroscopy verifies the existence of only very small quantities of isocyanurate groups. This experiment is repeated, this time employ- ing 1.0 gram of the epoxy resin, 9.0 grams of toluene diisocyanate and as the catalyst 0.36 grams (1.23 mmols) of tri-n-butylantimony and 0.3 gram (1.18 mmol) iodine. The reaction is conducted for 8 min. at 150° C. The analysis of this product again shows the form- ation of essentially no trimerized isocyanaurates. Examples 3 to 7 Isocyanate terminated oxazolidone precursors are prepared from a brominated bisphenol A/epichloro- hydrin epoxy resin having an equivalent weight of about 325, toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) and an triorganoantimony di- or tetraiodide catalyst as indicated in the following table. The reaction conditions are also specified in the following table. All of these reactions produce isocyanate terminated oxazolidone polymer precursors containing insignificant quantities of trimerized isocyanates. TABLE I Example Catalyst Reaction NO: Starting Material Volume (ml) Type Amount Temp(°C) Time( 3 30 wt% epoxy resin in TDI 25 ml Ph 3 SbI 4 0.34g 150-175° 10 4 30 wt% epoxy resin in MDI 50 ml Ph 3 SbI 4 0.80g 95 30 5 21 wt% epoxy resin in MDI 25 ml Ph-Sbl- 0.19g 85-115 20 6 20 wt% epoxy resin in MDI 25 ml Ph 3 sbi 4 0.27g 95 20 7 40 wt% epoxy resin in MDI 50 ml Ph 3 sbi 4 1.08g 95-135 10 Example 8 In a test tube are placed 1 gram of a 3.5 functional epoxy phenol novolac resin, 9 grams toluene diisocyanate, 0.02 gram (0.057 mmol) triphenyl antimony and 0.03 gram (o.H8 mmol) iodine. The test tube and its contents are heated to 150°C for 20 minutes. Infrared analysis of the resulting isocyanate-terminated polymer precursor verifies the formation of oxazolidone groups, but does not reveal any detectable isocyanurate. Example 9 In a test tube are reacted at 150°C for 20 minutes, 1 gram of a 320 equivalent weight epoxy- ter inated poly(propylene oxide), 9 gram toluene diiso¬ cyanate, 0.02 gram (0.057 mmol) triphenyl antimony and 0.03 gram (0.118 mmol) iodine. Infrared analysis verifies the existence of oxazolidone groups in the product, but no isocyanurates are detected. The resulting isocyanate-terminated polymer precursor has an average molecular weight of about 1000. Example 10 To one equivalent (163.3 g) of a triglycidyl ether of 4,4' ,4"-trihydroxy triphenyl methane are added, at 95°C, 0.44 g (1.25 mmol) triphenylantimony and 0.64 g (2.52 mmol) iodine. Isophorone diisocyanate, 11.1 g (0.1 equivalent) is then added and the mixture heated to 150°C. After reacting for six hours at 150°C, the product epoxy-ter inated polymer precursor contains 88 mole percent oxazolidone and 12 mole percent residual carbamate groups, with essentially no trimer. The equivalent weight of the product is about 206. To 80 gram of the polymer precursor is added 19.2 gram methylene dianiline to form a cured epoxy resin. A film cast from the curing resin exhibits excellent thermal stability. Example 11 To one equivalent (163.3 g) of a triglycidyl ether of 4,4' ,4"-trihydroxy triphenyl methane are added, at 110°C, 0.44 g (1.25 mmol) of triphenylanti¬ mony and 0.64 g (2.52 mmol) iodine. Toluene diisocy- anate (2.68 g, 0.031 eq) is added and the reaction mixture is heated at 105°C for 20 minutes. Hexamethyl- ene diisocyanate (HMDI) (3 ml, ~0.035 eq) is then added and allowed to react for ten minutes, at which time an additional 0.11 eq of HMDI are added. The mixture is then permitted to react an additional 6 hours at 110°C. The product epoxy-terminated polymer precursor contains 3 mole percent isocyanurate groups.

Claims: 1. A process for preparing a polyoxazolidone by reacting together a polyepoxide and a polyisocyanate, characterized by reacting said polyepoxide and polyiso¬ cyanate in the presence of a catalytic amount of an organoantimony iodide. 2. The process of Claim 1 characterized in that the organoantimony iodide catalyst is represented bythe formula R χ sbi y wherein x and y are each numbers from 1 to 4 provided that the sum of x plus y is equal to or less than 7 and each R is independently an aliphatic, cycloaliphatic, aromatic or aralkyl group or an inertly-substituted aliphatic; cycloaliphatic, aromatic or aralkyl group. 3. The process of Claim 2 characterized in that the antimony atom has an oxidation state of +5, x is a 3 and y is 2 or 4. 4. The process of Claim 3 characterized in that each R is independently an aromatic group having from 6 to 12 carbon atoms, a C 4= C 12 alkyl group or alkoxylated or halogenated derivatives thereof, a benzyl group or inertly substituted benzyl group. 5. The process of Claim 4 characterized in that the organoantimony iodide comprises triphenyl- antimony tetraiodide. 6. The process of Claim 3 characterized in that the molar ratio of the polyepoxide to the polyiso¬ cyanate is from 1:10 to 10:1. 7. The process of Claim 6 characterized in that an excess of said polyisocyanate is employed and the polyoxazolidone contains terminal isocyanate groups. 8. The process of Claim 7 characterized in that said polyepoxide and polyisocyanate each have an average functionality of from 2 to 3. 9. The process of Claim 1 characterized in that said polyepoxide is a reaction product of a bis- phenol or halogenated derivative thereof with an epihalohydrin and said polyisocyanate is toluene diiso¬ cyanate, diphenylmethane diisocyanate, or mixture thereof.

Inventors: MARKS MAURICE J, PLEPYS RAYMOND A, MARKS, MAURICE, J., PLEPYS, RAYMOND, A.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: C08G18
IPC codes: C08G18