PROCESS FOR THE POLYMERIZATION OF PHENOLS AT LOW OXYGEN FLOW RATES

Abstract: The need for indirect cooling and for pure oxygen are decreased without offsetting disadvantages in the batch manufacture of polyphenylene ether resins by the catalyzed oxidation of hindered phenols, by introducing oxygen into the catalyst-phenol-solvent solution at such rate that about 1/4 to 3/4 of said phenol is in prepolymer state when about 1/3 to 2/3 of the charge of phenol has been added to the reaction mixture. Lengthening of the time over which the phenol is added decreases the proportion of the diphenoquinone byproduct which is formed.

Description: PROCESS FOR.THE POLYMERIZATION OF ' PHENOLS AT LOW. OXYGEN FLOW RATES The present invention relates to the manufacture of polyphenylene ether resins, and particularly relates to a method of controlling the rate at which heat is formed during the batch manufacture of these resins by the 5 catalyzed oxidation polymerization of hindered phenols. Background of the ' Invention The polyphenylene ether resins (often called "polyphenylene oxide resins") are a well-known large family of thermoplastic engineering plastics which alone and in admixture with modifying polymers,, lubricants, 10 fillers, pigments, etc., have found wide commercial use for the manufacture of articles which possess excellent impact resistance and resistance to high temperatures, organic solvents, and water. The articles include radio and television cabinets, hand tool and household appliance 15 housings, medical and surgical instruments, electric motor and automobile components, films, sheets, etc. The polymers are substantially composed of units having the theoretical formula: 20.. wherein Ar represents an aryl unit, the ether oxygen atom of one unit being connected to the next adjacent aryl unit, and n is a value sufficiently large (usually at least 50) so that the polymer has a softening point which is sufficiently high for the intended use of the polymer, 25 typically 150°C. The resins are generally prepared by the oxidative coupling in a volatile organic solvent containing the catalyst of one or more hindered phenols of the structure: wherein X and X' each designate an inert substituent and H (hydrogen) , and Y and Y' each designate an inert substituent. Methods for the preparation of the polymers and a wide variety of suitable catalysts and starting phenols are disclosed in Hay. U.S. Patents 3,306,874 and 3,306,875; Stamatoff U.S. Patents 3,256,358 and 3,257,357; Wieden et al, U.S. Patent 3,442,885; obyashi et al U.S. Patent 3,445,880; Nakashio et al U.S. Patents 3,573,257 and 3,658,945; Haaf U.S. Patent 3,737,479, and White U.S. Patent 4,165,422, which is the most relevant of the group- (see. example thereof) . Commercial interest has centered about the polymer which is prepared from 2,6-xylenol which has the theoretical . .structure: the resulting polymer is substantially composed of units having the theoretical structure: wherein n has the meaning given above. The polymers are usually prepared by the batch method, by slowly pumping a charge of a solution of the desired polymerizable phenol or mixture of polymerizable phenols into a cylindrical reaction vessel which contains a solution of the desired catalyst and an oxygen supply tube extending to the bottom of the vessel. The catalysts and phenols usually have, limited solubility, and consequently the solvents which are used are usually the low molecular weight hydrocarbons or halocarbons or mixtures of these with alcohols, esters or ketones, all of-which are voltaile. The charge of the phenol or mixtures of phenols in an appropriate solvent is slowly pumped into the reactor containing the catalyst solution, and oxygen is introduced into the mixture with vigorous agitation in an amount which is in excess of the stoichio- etric requirements of the phenol component. A vigorous reaction takes place with evolution at the outset of much heat which decreases in the latter part of the polymerization. To maintain the temperature of the '_-_-__:..- reaction mixture safely below the decomposition point of the catalyst, the volatilization point of the solvent mixture present, and the temperature at which side __._.. reactions become significant, the reactor is provided with a jacket and interior cooling coils through which cold water or brine is circulated as required to prevent the temperature of the reaction mixture from rising above any of these danger points, generally taken to be 60°C. On completion of the reaction the polymer is recovered, the solvents are separated, and the catalyst is renewed. Details of the process and a variety of suitable catalysts and starting phenols are disclosed in the patents set forth above, which are hereby incorporated by reference in this specification. Various other ways of controlling the reaction have been tried without overcoming the foregoing disadvantages. Thus the use of less catalyst has been tried, but this decreases the rate of polymer molecμlar. weight increase; and slowing the rate at which the phenol solution is added also decreases the rate of polymer molecμlar weight .. _ increase. Slowing the rate at which the oxygen is added introduces the additional disadvantage of substantially increasing the proportion of less desirable dipheno- quinones which are formed as by-products. Thus in comparative laboratory trials a 2,6-xylenol-toluene solution was slowly pumped into a reactor containing a Hay copper-amine-bromine polymerization catalyst in toluene as solvent, and oxygen was introduced into the reaction mixture at a uniform rate with intensive stirring. When the oxygen was admitted in stoichiometric 3 excess (10 ft. , n.t.p. per hour), 0.99% of tetramethyl- diphenoquinone formed, based on the weight of the xylenol added. When the rate of admission of oxygen was 3 successively decreased to 5, 3 and 1.5 ft. /hr. , the amount of tetramethyldiphenoquinone which formed increased to 1.25%, 1.28% and 1.60% respectively. The discovery has now been made that the foregoing disadvantages and particularly the high initial release of heat can be substantially overcome without introduction of any serious new disadvantage by "starving" the reaction mixture of oxygen during the period over which the phenol- solvent charge is added to the reactor and by concurrently increasing the length of the time over which the phenol- solvent mixture is added, so that essentially only pre- polymerization of the phenol occurs during this period, and then if desired increasing the rate of oxygen admixxion during the latter phase of the polymerization, the oxygen then if desired being added in excess. The further discovery has been made that still better control of the release of heat during the reaction can be effected by using air as the source of oxygen during at least the first phase of the polymerization, which also permits a substantial saving in the cost of operating the process, and extending to at. least 20 minutes the duration of the step of charging the phenol into the reactor. The invention provides the following additional 5 advantages: 1. The initial surge of exothermic heat is moderated, and the rate of evolution of heat is more or . less leveled over the course of the reaction. As a result, in certain instances, depending, principally on the. volume: surface 10 ratio of the reaction vessel, the interior cooling coils can be eliminated entirely or their size substantially decreased. As a result, the capacity of the reactor is increased, its capital cost is lessened, and the task of cleaning the interior of the reactor is made easier. 15 2. The process does not require any new equipment or costly or delicate controls. The process is adapted for use in presently existing polymerization reactors. 3. Deactivation of the catalyst during the polymerization is usually less serious than has been 20 heretofore experienced, permitting a significant cost saving. More in detail, according to the invention a fluid solution of a polymerizable phenol in an inert volatile organic liquid at about room temperature is added as a 25. stream to a solution of a catalyst in a similar liquid, and oxygen is admitted as a stream into the reaction _ mixture at such a rate that oxidation of the phenolic hydroxy groups to ether groups takes place at a substantially constant rate during admixxion of the 30 phenolic component to the reactor. As a result, a substantial portion of the phenolic component is in low molecular weight or pre-polymer state when much but not all of the .phenolic component has been added. The reaction mixture is intensively agitated so as to disperse the 35 oxygen in small bubble or foam state throughout the reaction mixture to ensure that substantially all of the oxygen, at least during the initial phase of the polymerization, reacts with the phenol so as to cut losses of oxygen to a minimum. In the initial phase of the polymerization, air can be economically employed as the source of oxygen. The precise rate at which the oxygen is admitted to the reaction mixture depends on a number of independent variables, for example the molecular weight of the phenol (or mixture of phenols, hereinafter for convenience termed "the phenol") , the rate at which the phenol is supplied to the reactor, the. temperature of the reaction mixture, the efficiency of the catalyst which is employed, and the ratio of the volume of the reactor to the area of its cooled surface. A suitable oxygen admission rate in any instance can be readily found by a series of trials, the preferred rate being generally that which maintains the temperature at a level just below the decomposition point of the catalyst (usually 25°C. to 60?C), the temperature at which side reactions become significant, or the temperature at which the solvent volatilizes to more than a negligible extent, whichever is the lower. In the polymerization reaction, with introduction of the phenol and oxygen at constant " rate, the concentration of reactive hydroxy groups in the reaction mixture slowly increases as the polymerization advances until all the phenol.has been admitted, and then falls as the reaction proceeds. During the first part of the polymerization, therefore, the rate of admission of oxygen, according to the present invention, is less than that which is stoichiometrically equivalent to the phenolic hydroxy groups. As a result, the phenol component is "starved" for oxygen during this phase of the reaction. In proportion as the concentra¬ tion of hydroxyl groups to phenolic groups changes, the quantity of oxygen admitted to the reaction is controlled so as to keep substantially constant the rate per unit of ti e at which the hydroxy groups are oxidized to ether groups. Preferably the rate is such that the temperature of the reaction mixture is less than 50°C. when l/2_of the phenol-solvent charge has been added to the reaction mixture. The aforesaid oxidation reaction is not self-sustain¬ ing, and the heat which it releases is a direct function of the quantity of oxygen which has been reacted. Accordingly, it is advantageous to introduce pure or substantially pure oxygen in an excess for a brief period at the start of the reaction, so as to bring the reaction mixture to its optimum reaction temperature and so to bring this phase of the polymerization to a conclusion as quickly as possible. The product of this phase of the polymeri- zation is predominantly a mixture of low oligomers of the phenol (that is, low molecular weight prepolymers) including dimers, trimers and tetramers, plus a substantial proportion of the phenol in unreacted state. In practice, the foregoing means that the oxygen is introduced or:.injected into the reaction mixture at such a rate that between about 1/4 and 3/4 by weight of the added phenol (i.e. , the weight of phenol which has been added to the reaction mixture) is in the aforesaid low oligomeric state when between about 1/3 and 2/3 of the charge of the phenol has been added, that is, when the addition of the phenol to the reaction mixture is between about 1/3 and 2/3 complete. Preferably the rate of admixxion of oxygen is such that at least 1/2 of the weight of said added phenol is in low molecular weight oligomeric state when about 1/2 of the phenol-solvent charge has been added. In order to introduce oxygen at a low rate and yet not build up a high concentration of unreacted phenol, which can produce more by-product diphenoquinone, it is desirable to add the phenol at a slower rate than is normally possible with the Hay catalyst (which had led to retardation of the polymerization) . Surprisingly we find that when the oxygen is added at a slow rate, the phenol can also be added at a slow rate. Two principal advantages result from this combination. First, the evolution of heat is spread out over a longer period of time, so that the reactor requires less cooling capacity. Second, less diphenoquinone is formed. The catalyst which is used to promote the oxidation reaction should be non-hydrolyzable since the polymeriza- tion reaction results in the formation of a considerable amount of water. For this purpose the Hay catalysts (disclosed in the aforementioned patents) are preferred since they are very resistant to hydrolysis, are easily prepared, and possess good resistance to decomposition or deactivation under reaction conditions. These catalysts are complexes in a volatile inert solvent of a cuprous compound or cupric compound and one or more amines and a halogenide, preferably a bromide. If desired, the catalysts can contain a lower (C-. _g alkyl) secondary amine to improve the impact resistance of the polymer. If preferred, any other non-hydrolyzable catalyst can be employed, for example, one of the highly reactive manganese salt (chloride, sulfate, etc.) - benzoin oxime catalysts wherein the benzoin oxime is present as ligand. The solvents referred to above can be any volatile organic liquid which is inert and which possesses the necessary solubility characteristics. Aromatics such as benzene and toluene are suitable, but it is preferable to have a substantial amount of a lower alkanol present such as methanol and/or ethanol to receive the water which is formed in the reaction. The process is at an end when a polymer has formed which has a softening point which,is sufficiently high to render it practically useful, for example 150°C. and preferably 200°C. The reaction is halted by switching the supply of oxygen (or air) to nitrogen followed by addition of trisodium ethylenediaminetetraacetate, after which the catalyst is separated, and the polymer recovered. The invention is thus an improvement in a batch- process for the manufacture of a polyphenylene ether resin by the catalytic oxidation polymerization of a phenol, wherein a fluid charge of a polymerizable phenol in an inert volatile organic solvent is added as a stream to a solution of a polymerization catalyst in a. voltaile organic solvent, and oxygen is introduced as a stream into the resulting mixture with agitation of the mixture to form a uniform dispersion of. the phenol, the catalyst and the oxygen, until a resin has formed which has a softening point in excess of 150°C. , the improvement being introducing said oxygen into said mixture at rate that between about 1/4 and 3/4 by weight of said added phenol is in low oligomeric prepolymeric state when between about 1/3 and 2/3 of said charge of said phenol has been added. The invention includes the additional step .of increasing the length of the addition time for the introduction of the phenol-solvent solution to said mixture, thereby enabling the rate of oxygen introduction to be decreased without production of additional diphenoquinone by¬ product. The invention is further described in the examples which follow. These examples are preferred embodiments of the invention, and the invention is not to be construed as limited thereto. EXAMPLE 1 The following illustrates the process of the present invention wherein a Hay-type catalyst is used and wherein the oxygen is injected at such rate that about 1/2 of the added phenol is in low oligomeric prepolymer state when about 1/3 of the phenol-solvent charge has been added to the reaction mixture. Into a 2.5-gallon water-jacketed stainless steel reactor equipped with paddle stirrer, oxygen inlet tube O extending to the bottom.of the reactor, interior cooling coils and viscosity monitor " (a pressure gauge mounted on a sampling loop through which the reaction mixture is constantly circulated) are charged at room temperature 3.3 5 liters of toluene as diluent, 62 ml. of laboratory catalyst stock solution (made by adding 23.1 ml. of bromine slowly to a chilled solution of 6.21 g. of cuprous oxide and 86.8 g. of 2,6-xylenol in methanol and diluting the mixture to 0.5 liter with methanol), 679. l. of 95% 10 methanol, 1.85 g. of N,N'-di-t-butylethylenediamine, 21.8 g. of butyldimethylamin , 12.0 g. of di-n-butylamine, and 1.2 g. of Aliquat 336 (a quaternary ammonium surface- active agent). The mixture is intensively stirred, oxygen at room temperature'is introduced into the 15 mixture through the inlet tube at the constant rate of 3 3.0 ft. (n.t.p.) per hour, and a solution of 1.2 kg. of 2,6-xylenol in 1.33 liters of toluene is pumped into the mixture in 56 minutes. The reaction temperature rises from 18°C. to 24°C. in five minutes and from 24°C. to 20 40°C. in about 15 minutes, at which point analysis of the reaction mixture by gas chromatography shows that at least half of the xylenol which has been added is in low oligomeric (prepolymer) state. The reaction temperature is maintained at 40°C. by admission of cooling 25.- water into the jacket and the interior coils until completion of the polymerization. During the polymerization, tetramethyldiphenoquinone is formed and the amount which is present is determined at intervals by removing, during the first part of the 30 polymerization 5-ml. samples of the reaction mixture, immediately diluting the samples to 100 ml. with benzene, then diluting 5-ml. portions of the resultant solutions to 100 ml. , and analyzing the portions spectrophotometri- cally at 423 nm. In the latter part of the polymerization, 35 2-ml. samples are sufficiently large for the second dilution. The polymerization is terminated 90 minutes after the start of the addition of the xylenol (and therefore 34 minutes after completion of the addition of the xylenol) by replacing the oxygen with nitrogen and adding 16 ml. of a 38% by weight solution of trisodium 5 ethylenediaminetetraacetate in water. The reaction mixture is transferred to a large open vessel equipped with a paddle stirrer, and three volumes of methanol are added to precipitate the polymer. The polymer is collected on a filter, washed with methanol and dried. 10 The intrinsic viscosity of . polyphenylene ether is 0.56 dl./g., the weight of tetramethyldiphenoquinone in the reaction mixture is 1.07% of the weight of xylenol added, and the softening point of the polyphenylene ether product, after injection molding, is over 150°C. 15 ' EXAMPLE 2 The following illustrates the controlled addition of the phenol component and of the oxygen to prevent " the rate of formation of heat in the reactor from rising above a safe level. 20 The procedure of Example 1 is repeated, except that the rates at which the phenolic component and the oxygen are added are decreased after the temperature of the reaction mixture has risen to the desired level. Initially, 400 g. of 2,6-xylenol (one-third of the total amount to 25. be added) is added to the reactor over a 10-minute period, and oxygen is supplied to the reactor at a flow 3 rate of 8.3 ft. per hour, during which time the temperature of the reaction rises from 24°C. to 40°C. The rate of flow of the oxygen is then decreased to 3.0 3 . 30 ft. per..hour, and the rate of addition of the xylenol is decreased so that the remaining 800 g. of the xylenol is added in 48 minutes. By these means the temperature of the reaction is controlled at 40°C. The polymeriza¬ tion is terminated 86 minutes after the start of the 5 addition of the xylenol ' (and therefore 28 minutes after completion of the addition of the xylenol) . The polymer ^ " RE is isolated by coagulation with methanol, collected by filtration and dried in vacuo at 70°C.-80°C. The intrinsic viscosity of the polymer is 0.56 dl./g.; the weight of tetramethyldiphenoquinone in the reaction mixture 5 on-..conclusion of the reaction is 0.95% of the weight of the xylenol shich was added. EXAMPLE 3 The following illustrates the polymerization of a polymerizable phenol under highly oxygen-starved conditions, 10 so that advancement of the phenol beyond the low molecular weight oligomeric stage is slight during. the first half of the addition of the phenol, with consequent decrease in the amount of heat which is formed in the reaction mixture. The procedure of Example 1 is repeated except 15 that the rate of admission of oxygen is decreased to 1.5 ft. /hr. and the oxygen is replaced by air (admitted at the same rate) when the temperature of the reaction mixture reaches 40°C. The viscosity of the reaction mixture does not' sensibly increase until 30 minutes after 20 all the xylenol has been added, showing that at least 1/2 by weight of the added xylenol is in an oligomeric state when about 1/2 of the xylenol-solvent charge has been added. The temperature of the reaction mixture is held at 40°C.-50°C. by circulating cold water through the 25.- jacket alone. When all the xylenol has been added, the supply of air is gradually replaced by oxygen so as to maintain the temperature in that range without use of the interior cooling coils. A similar polymer is obtained. EXAMPLE 4 30 The following further illustrates the use of air as the source of oxygen. The procedure of Example 1 is repeated except that the xylenol is added over 30 minutes and air at room 3 temperature is supplied at the rate of 15 ft. per hour, 3 35 which provides oxygen at the rate of 3. ft. per hour. In the absence of external heating and cooling the ' , gU OM reaction temperature increases from 23°C to- 40°C in 63 minutes. The reaction is terminated.181 minutes after the start of addition of the xylenol. The weight of tetramethyldiphenoquinone in the reaction mixture is 5 1.4% of the weight of the xylenol which was added. The intrinsic viscosity of the isolated polymer is 0.57 dl./g. • EXAMPLE 5 The following illustrates the use of a controlled rate of oxygen flow to maintain at a safe, level the rate 10 of release of heat in a xylenol polymerization catalyzed by a manganese-benzoin oxime complex. The reactor described in Example 1 is charged with 180.0 g. of 2,6-xylenol, 3.2 liters of toluene as diluent, 900 ml. of methanol, 48.0 of 50% sodium hydroxide 15 solution and 18.0 g. of di-n-butylamine, all at room temperature. The mixture is intensively stirred and - oxygen at room temperature is introduced into the " mixture 3 at the constant rate of 10 ft. per hour for 3 minutes, immediately followed by a solution of 2.98 g. of i-benzoin 20 oxime and 0.824 g. of M Cl^ dissolved in 100 ml. of methanol. A solution of 1080 g. of 2,6-xylenol in 1150 ml. of toluene is-then added over 38 minutes. Nine minutes after the start of the addition of the xylenol solution the desired reaction temperature of 28°C. is ' 25. reached and the rate of flow of the oxygen is decreased 3 to 3 ft. perhour. This temperature and rate of oxygenation are maintained until completion of the polymer¬ ization. The reaction is terminated 120 minutes from the start of the addition of the xylenol solution. 30 The weight of tetramethyldiphenoquinone in the :_ reaction mixture is 0.80% of the weight of the xylenol added. The intrinsic viscosity of the isolated polymer is 0.68 dl./g. EXAMPLE 6 35 The following illustrates the use of a combination of air and pure oxygen to supply oxygen to the reaction - U OM 3 mixture at a flow rate of 3 ft. per hour. The procedure of Example . 1 is repeated except that 3 a combined stream of air (7.5 ft. per hour) and oxygen 3 (1.5 ft. per hour) is injected into the reaction mixture. The xylenol is pumped into the reactor in- 58 minutes. The reaction temperature increases from 25°C. to 40°C. in 32 minutes. The reaction is terminated 141 minutes from the start of the addition of the xylenol. The weight of tetramethyldiphenoquinone is the reaction mixture is 1.5% of the weight of the xylenol which was added. After isolation, the polymer has an intrinsic viscosity of 0.54 dl./g. The above patents and/or publications are incorporated herein by reference. Obviously, many variations will suggest themselves to those skilled in this art in the light of the above detailed description. All such variations are within the full intended scope of the appended claims.

Claims: CLAIMS 1. In a batch process for the manufacture of a polyphenylene ether resin by catalyzed oxidation polymerization of a phenol, wherein a fluid charge of a polymerizable phenol in an inert volatile solvent is 5 added as a stream to a solution of a polymerization c _ catalyst therefor in an inert volatile organic solvent, and oxygen is introduced as a stream into the resulting mixture with agitation of the mixture to form a uniform dispersion of the phenol, the catalyst and the oxygen, 10 until a resin has formed which has a softening point in excess of 150?C. , the improvement which comprises: introducing said oxygen into said mixture at such rate that between about 1/4 and 3/4 by weight of said added phenol is in a lower oligomeric state when between 5 about 1/3 and 2/3 of said charge of phenol has been added. 2. A process ' according to Claim 1 wherein said phenol is 2,6-xylenol. 3. A process according to Claim 1 wherein said charge of phenol and solvent is at room temperature at the start of said process. 4. A process according to Claim 1 wherein the time of addition of said phenol to said catalyst solution is in excess of 20 minutes, whereby the exothermic portion - of the polymerization reaction is prolonged and control 5 of the temperature of the reaction by external cooling is facilitated. 5. A process according to Claim 1 wherein the rate at which said oxygen is injected into said mixture is such that at least 1/2 by weight of said added phenol is in an oligomeric state when about 1/2 of said phenol-solvent 5 charge has been added. 6. A process according to Claim 1' wherein the charge contains a soluble C-, ,- dialkylamine as component increasing the impact resistance of the polymeric product. "BU E OMP - 16 - 7. A process according to Claim 1 wherein the rate at which said oxygen is injected into said mixture is such that the temperature of said mixture is less than 50°C. when 1/2 of said phenol-solvent charge has been added to the mixture. 8. A process according to Claim 1 wherein said oxygen is_initially added in excess until the temperature of said reaction mixture rises at least to 40°C. 9. A process according to Claim 1 wherein said catalyst is a non-hydrolyzable copper-amine-halogen complex. 10. A process according to Claim 1 wherein said catalyst is a manganese salt - benzoin oxime catalyst wherein said benzoin oxime is present as ligand. 11. In a batch process for the manufacture of a poly¬ phenylene ether resin wherein a charge of a polymerizable phenol in a volatile organic solvent is added as a stream to a solution of a polymerization catalyst in a volatile organic solvent, and oxygen is injected as a stream into the resulting mixture with agitation of the mixture to form a uniform dispersion of the phenol, the catalyst and the oxygen, until a resin has formed which has a softening point in excess of 150?C, the improvement , which comprises: first injecting said oxygen into said mixture at such rate that about 1/4 to 3/4 by weight of said added phenol is in oligomeric state when about 1/3 to 2/3 of said phenol and solvent charge has been added, and then adjusting said rate at which said oxygen is injected into said mixture so that said oxygen is injected in excess; if necessary, the temperature of said mixture being maintained by indirect cooling below the inactivation temperature of said catalyst. 12. A process according to Claim 11 wherein the oxygen which is first injected into said mixture is a component of air. O P - 17 - 13. A process according to Claim 11 wherein injection of said oxygen at said excess rate is continued until said resin has a softening point in excess of 150°C. 14. A process acco-ding to Claim 11 wherein said excess oxygen injection rate is in the rate at which at least 1% of said injected oxygen constantly escapes from said mixture in unreacted state. _O P

Inventors: LOUCKS GEORGE RAYMOND, WHITE DWAIN MONTGOMERY, LOUCKS, GEORGE, RAYMOND, WHITE, DWAIN, MONTGOMERY
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1982
Main classification: C08G65
IPC codes: C08G65