2,408,426 Patented Oct. 1, 1946 “ UNITED STATE 5 i PATENT OFFICE 2,408,426 ~ PREPARATION OF MODIFIED METHYL METHACRYLATE COMPOSITIONS Frederick L. Johnston, Claymont, Del., assignor to E. I. du Pont de Nemours & Company, Wil mington, DeL, a corporation of Delaware ' . No Drawing. Application January 12, 1943, Serial N0. 472,161 (CL 260-83) 2 Claims. 1 This invention relates to the preparation of" modi?ed methyl methacrylate compositions and, more particularly, to such compositions adapted , to give molded articles characterized by high re sistance to distortion by heat. Heretofore methyl methacrylate monomer has been polymerized to yield thermoplastic molding compositions. When such polymers are prepared In the preferred method of, carrying out this small amounts of benzoyl peroxide and the selected halo-ole?n are dissolved in methyl . invention, methacrylate monomer. This solution is sus pended in about twice its volume of water. water contains a small proportion of a mild dis persing agent such as the 65% sodium salt of poly methacrylic acid and is buffered to a pH of about 7.5 by means of a suitable inorganic salt. This by heating methyl methacrylate monomer in the mixture is agitated vigorously in a closed reac 10 absence of catalysts or in the presence of small tion vessel capable of withstanding moderate concentrations of peroxide-type catalysts, the re pressures. The polymerization is carried out by sulting molding compositions are difficult to fuse heating at a temperature in the neighborhood into optically homogeneous masses under heat of 125° C. under a pressure of about 50 lbs/sq. in. and pressure, and, when hot, are too viscous for 15 for twenty to thirty minutes until the essential satisfactory molding by injection.» In the past these objections have been partly overcome by completion of polymerization is indicated by a various means but an outstanding dif?culty has been to obtain a product which can be molded into, articles that do not tend to distort at undesirably appearance of monomeric methyl methacrylate. sudden drop in pressure due to the essential dis It is preferable to prevent the reaction from be coming too violent by suitable cooling of the ves low temperatures; particularly, has this been the 20 sel. The mixture is then cooled and discharged case where the articles have been injection mold from the reaction vessel. The granular product ed although it also holds to a considerable extent with respect to compression molded articles. A further di?lculty is to obtain a product improved in this characteristic and at the same time char acterized by good moldability and yielding mold ed products having optical homogeneity and being is separated from the mother liquor, washed, cen trifuged, and dried by heating at 70° C to 100° C. in a circulating air oven or under vacuum, and 25 this dried granular polymer is then masticated on hot mixing rolls for ten to ?fteen minutes, re moved from the rolls, cooled and comminuted to pass a %" screen. Thev resulting product is suit free from discoloration. An object of the present invention is to provide 30 able for compression or_ injection molding and an improved methyl methacrylate composition shows special advantages when used for the lat characterized by good moldability and adapted to be molded into articles having high resistance to distortion by heat, optical homogeneity, and free ter purpose. ‘ The following examples illustrate speci?c em bodiments of the composition and the method of dom from discoloration. A further and more preparing same according to the present inven particular object is to provide a composition 35 tion, all parts being given by weight unless other- _ adapted to be injection molded into articles hav ‘ wise specified: ing high resistance to distortion by heat. A still Exmu: I further object is to provide a practical and eco nomical method of preparing such compositions. 40 Other objects will be apparent from the descrip tion of the inventiongiven hereinafter. The above objects are accomplished according (a) The following solutions are made up of: > Parts Distilled water _________________________ __ to the present invention by polymerizing mono NazHPO4.12H2O meric methyl methacrylate in the presence of very 45 1% Water solution of ‘small amounts, of unsymmetrical alpha-ole?nic 4800 '56 polymethacrylic acid --_,_____________ __ ‘compounds in which one of the carbon atoms of the double bond carries a single, halogen atom. More speci?cally, the polymerized methyl meth acrylate composition of the present invention is 50 prepared by polymerizing a dispersion of mono meric methyl methacrylate in a non-solvent liq uid such as water in the presence of 0.01% to 3.0%, by weight of the monomer, of an unsym (b) . ‘ Parts Methyl methacrylate monomer __________ .._ 2786 Octadecyl alcohol (lubricant) ___________ .._ 56 Trichloroethylene _________ __l____.'. _____ __~ 14 (c) Benzoyl peroxide _______________________ -_ 'l metrical alpha-ole?nic compound in which one of the carbon atoms of the double bond carries a 65 The ingredients in (a) are dissolved together - single halogen atom, at a temperature of 100° C. and charged into a glass enamel‘ vlined closed re 150° C. under autogenous pressure. 9,408,426 3 action kettle capable of withstanding pressures up to 300 lbsJsqin. and ?tted with a stainless steel anchor shaped stirrer, stainless steel ba?les, thermocouple for observing the temperature of the contents, and an outlet through the head to a tioned in this speci?cation are determined by this pressure ‘gauge. The catalyst (c) is freshly dis solved in (b) and the resulting solutionis charged at once into the reaction kettle. method. \ A similar methyl methacrylate polymer poly The kettle is sealed and the stirrer operated at 575 R. P. M. throughout the run. External heat is applied to bring the kettle contents, to a temperature of 110° C. within ?fteen to twenty minutes at which time the pressure gauge shows about 45 lbs./sq.in. pressure. The heat is then shut oil". Within one to two minutes the exothermic polymerization re 15 action begins and there is a surge of‘ temperature and pressure to 114° C. and 53 lbs./sq.in., re spectively, where the bulk of the polymerization takes place. Within about. ?ve minutes there is a rapid decrease in pressure to about 15 lbs./sq.in. 20 and the temperature begins to drop. Stirring is continued until the kettle contents have cooled to 40° C. or. below at which time the pressure The above example is repeated using varying quantities of trichloroethylene. When the prod ucts are worked up and molded as above, injection molded softening temperature specimens are ob tained which soften vas shown in the following table: Softening-tom ra Oonocntmtion of trichlmoethylcno (based on methyl methacrylate monomer) gauge shows zero pressure and the kettle is opened. The product, in the form of crystal clear 25 spherical granules up to about 1/64" diameter, is removed from the mother liquor on ?lter cloth 0.0 . (blank for control).................... -- 0.25% _____ __ 0.75% 2.00%’. cction ° C. 64 82 0.50” 86 _- 85 1.00% ________________________________________ __ the washings are clear. This requires a total of ture of molded sinj en 84":24' x0.065" .... -_ 91 85 about 20,000 parts of wash water. Excesswater 30 is removed by means of a centrifuge and the prod not is dried at 100° C. for‘24 hours under high vacuum. I a The ?ne granular product is converted to mold ing powder suitable for injection molding by hot 35 pressing into sheets at 160° 0., followed by chop ping into particles which will pass a %” screen. Exam: I! The ingredients for a granular polymerization are assembled as follows‘ ' l\ (in Parts Distilled water________________________ __,- 4800 NazHZPO4J2HzO ______________________ __ This molding compound is then injection molded in an injection molding machine, suitably a 1% Water solution of 65% sodium salt of l-ounce capacity De Mattia vertical injection 40 molding machine built by the De Mattie. Machine and Tool Company, Clifton, N. J. The machine‘ polymethacrylic acid. ______________ ..-__ (b) _ 480 Parts Methyl methacrylate monomer__________ __ 2786 2-Chloropropene is supplied with a die capable of molding test specimens whose measurements are 21/2" x 1/z" x 0.065". The polymer is injected into the die 45 Benzoyl peroxide ___.._.._ ______ __....____.,-_ ' Cc) 14 Parts '7 through agate at the end of the‘ cavity ‘with the die closing and injection taking place during a The ingredients are charged into a kettle as de scribed in Example I and polymerization is con period of 1.25 seconds. The machine is timed ducted in a similar manner. Heat is applied as in to maintain piston pressure on the molding pow der and clamping pressure on the die simultane 50 Example I and after the heat has been cut off the exothermic polymerization reaction causes a ously for ?fteen seconds to enable the molding to surge of temperature and pressure to 125° C. and set up in the die. A new injection is made every 70 lbs/sq. in., respectively. The bulk of the poly sixty seconds. The polymer may be molded under merization takes place under ' these conditions. several temperature conditions to yield speci mens of attractive appearance. ~ When the heat 55 The resulting polymeris worked up and converted to molding powder and injection molded in the ing cylinder delivers polymer. at 220° C. into the manner described in Example I.’ When the heat cold die, satisfactory moldings are produced un ing cylinder delivers polymer at 230° C. into the der 22,700 lbs./sq.in. piston pressure.‘ Moldings cold die, satisfactory moldings are produced un of excellent clarity and surface characteristics are obtained which are faithful reproductions of the 60 der 25,700 lbs./ . in. piston pressure. The mold ings obtained are brilliantly clear and are faith die cavity. Injection moldedstrips molded as ful reproductions of the die cavity. Injection above are found to “soften’? at 86° C. according to the following method. molded strips from the 2%“1: K" x 0.065" die soften at 99° C. according to the softening te The strip 2%" x 1/2''' x 0.065" is mounted perature determination described under Exam horizontally by one end in a clamp, cantilever 65 pie 1 " . . fashion, the supported end sticking 14" into a A similar methyl methacrylate polymer poly vertical slot in the clamp so that the strip is sup ported 34;" from the end. At a spot 1A" from the - merized as above but without the addition of 2-chloropropene and converted to molding powder opposite end on the upper edge a weight of 27.5 g. is placed so that it rests entirely on-the test strip 70 in the same manner yields injection molded test strips which soften at 74° C. by the above deter and is free to move up or down with the strip. The assembly (excepting the weight) is immersed in a bath of circulating mineral'oil which is uni formly heated at a‘ steady rate of 2° C. per minute.‘ The “softening” temperature is observed-as that mination. Example II is repeated using vof 2-chloropropene. When the quantities products are ' worked up and molded as above, injection molded 75 softening temperature specimens are obtained 3,403,490 . 5 6 It will be understood that the above examples are merely illustrative and that the present in vention comprises, in its broader. aspects, the whose softening temperatures to the method decribed under Example I are as follows: polymerization of monomeric, methyl methac . soitcnlngtemnew 5 rylate in the presence of small amounts of any unsymmetrical aipha-ole?nic compound in which w“ ° mm‘ ' Oonoentrationoi methyl mstbm (baled mine!) on gl?jflsd‘lp?w? one of the carbon atoms of ‘the double bond carries a single halogen atom‘, to obtain a prod uct especlally'suited for injection and compres ' c. 10 :1 (blank for control) ...................... -- ‘a: .i "f, ........................................ -_ w so ' sion molding. unsymmetrical alpha-ele?nic compound as here-' in de?ned. The structure and constitution of the rest of the molecule of the halo-ole?n is rela w mam-l III (0) tively immaterial as long as it does not contain chromophoric structures which would impart is- A polymerization is carried out using the follow ing ingredients: Distilled water ' The invention contemplates the use of any color to the product or functional groups that inhibit the polymerization of methyl methac rylate. In order to avoid the cumbersome and Parts 4800 Na:HPO4.l2HaO _____________________ .. 56 20 impractical use of gaseous modi?ers, it is pre ferred to employ halo-ole?ns of molecular weight above 70 and chloro-ole?ns are preferred. Compounds which are closely related chemi ((1)) Parts cally to the herein speci?ed halo-ole?ns but Methyl methacrylate monomer__________ __ 2772 which do not fall within the speci?c de?nition 1-Chloro-3-hydroxypropene-1 __________ __ 28 25 of being unsymmetrical alpha-ole?nic com 1% Aqueous solution of the 65% sodium salt of polymethacrylic acid ________ m _____ .._ (c) 600 Parts Benzoyl peroxide __-_ pounds in which one of the carbon atoms of the double bond also carries a single halogen atom, 7 fail to produce signi?cant improvements in The above ingredients are polymerized accord 3“ methyl methacrylate polymers. Thus if the ing to the general method described in Example process of Example II is ‘repeated using small I. ' The bulk of the polymerization takes place at a temperature of 121° C. under a pressure of 48 ‘ concentrations of other chlorine containing compounds closely related to 2-chloropropene, trichloroethylene, etc., the following results are is worked up and injection molded according to the general me od described in Example I, poly 35 obtained: granular polymer mer delivered from the heating cylinder at 220° C. is readily injection molded into specimens of excellent appearance under a piston pressure of 23,300 lbs/sq. in. Aspecimen 2%" x 1b" x 0.065" is found to soften at 87° according to the method described in Example I. A correspondingun modi?ed control polymer softens at 74° C. Exmnl IV The following solutions are made up: (a) ~ , Softening tempera ture of injection moldedspecimen 2%”x%’ X0065” Concentration of modi?er (based on methyl methacrylate monomer) 40 ' I .0% (blank ior control) ...................... _. .507 tetrachloroethylene __________ __ .15‘?a dlcbloroethylene. 4% symmetrical symmetrical dichioroethylenen 2 as’; _ carbon tetrachloride ...... . Parts Distilled water_________________________-- 4800 NamPOamHsO __._ ____________________ __ 56 1% Aqueous solution of the 65% sodium salt of polymethacrylic acid. ____________ _._.__ (12) 600 Parts Methyl methacrylate monomer_________ ..._.. 2772 Methyl alpha-chloracrylate monomer ____ __ 28 In general, the use of the speci?c halogenated 50 ole?ns de?ned above as modi?ers for methyl methacrylate according to this invention leads to polymers that show superior heat resistance in injection molded specimens. However, the concentration of the particular halogenated ole on the properties Parts 55 ?n has an important bearing and equivalent e?ects are ' of the molded product, Benzoyl peroxide 7 obtained with different concentrations for each The above ingredients are polymerized in the speci?c halogenated ole?n. This is obvious in general manner described in Example 1. During view of the differences in activity of the various the exothermic polymerization reaction the bulk e0 modi?ers contemplated and their di?ering rela of the polymerization takes place at a temperative molecular weights. In general, the concen ture of 126° C. under a pressure of 55 lbs./sq. in. tration of speci?c halogenated ole?n required is when the resulting granular polymer is worked ' greater the higher the molecular weight of the up and injection molded, polymer delivered from speci?c halogenated ole?n. But only relatively the heating cylinder into the injection die at 200° 65 small amounts of the modi?ers de?ned above - C. molds readily under a piston pressure of 23,300 are required, and the present invention contem lbs/sq. in. An injection molded specimen plates the use of these modifiers in concentra 21/2" x 9611' x 0.065" is ‘found to soften at 89° C. tions only up to about 3% by weight of the methyl according to the softening temperature determi methacrylate monomer. Particularly with very nation described under Example I. 70 active modi?ers, concentrations as low as 0.01% The above example is repeated using 2% of produce signi?cant improvements. methyl alpha-chloracrylate monomer (based on It is preferredto carry out the present inven tion by polymerizing methyl methacrylate com- _ ' methyl methacrylate monomer) instead of 1% and an injection molded specimen 21/2" x Vi" x positions'while dispersed in a non-solvent such 0.065" is found to soften at 95° C. as compared 75 as water. Temperatures of polymerization may to 74° C. for an unmodi?ed control. (c) 2,408,426 7 8 be from 100° 0. up to temperatures of 150° C. or higher, with a temperature oi.’ at least 125' C. size may be used on products oi’ the present in vention. - preferred, in closed reaction equipment suitably designed to withstand the autogenous pres- Plasticizers or lubricants may be added to the products of this invention either during poly sures developed. As the reaction temperature is 5 merization as in Example I or during subsequent increased,_ the‘concentration ot benzoyl peroxide mastication of the polymer 'on heated rolls. Suit about 1%, (based on methyl methaerylate monomer) at 100° C. to 0.5% in the range of 110° C. similar manner for imparting special appearance concentration is further decreased, and at temperatures of 150° C. and above the catalyst may articles by the known methods of compression or, injection molding commonly used for shaping eil'ects to the polymer. to 115° C. and to 0.25% in the range of 120° C. 10 The products of this invention are useful as to 130° 0. Above this temperature the catalyst molding powders for the preparation oi’ valuable .8 catalyst concentration is selected which yields 15 processloi’ injection molding, the products of this tion for optimum molding properties. Catalysts other than benzoyl Peroxide are used in corresponding amounts- V'I'hus didodecyl‘ ously known methyl methaerylate polymers in‘ ‘that the molded articles show a much greater resistance to distortion by heat while at the peroxide, diethyl peronide, hydrogen peroxide, 20 same time being optically horn and free and similar‘/ catafrom discoloration. The products of this inven ~ persuli'uric and its salts, lysts may beacid suitably used. The use of dispersants such as the 65% sodium rods. ' ‘ salt of polymethacrylic acid is‘ optional. The As many apparently widely diirerent embodi amount required generally varies in inverse ratio 25 ni'ents of this invention may be made without to the effectiveness of agitation during polymerdeparting from the spirit and scope thereof, it is ization. The amount and eifectiveness of the disto be understood that the invention is not lim persant selected, if any.>is preferably so limited ited to the speci?c embodiments thereof except a as to prevent the formation ofa permanent sus, as de?ned in the appended claims. _ pension and merely suincient to keep droplets 30 ,I claim:v ‘ _ of the methyl methacrylate compositions‘ from coalescing during polymerization. The water 1. Process of preparing a modi?ed methyl methacrylate omposition which comprises poly dispersant is the most effective. A pH of less 35 3.0% by weight of the monomer of trichloroethyl; than 4 or above 10 is generally to be avoided because of the tendency of methyl methacrylate ene at a temperature 01 100? C.-150° C. under . autog'enous pressure. - monomer to hydrolyze under these conditions. 2. A modi?ed methyl 'methacrylate molding The products of this invention can also‘ be precomposition adapted to be molded into articles pared by other methods of polymerization, such 40 having a high resistance to distortion by heat Any of the customary methods for converting weight of the monomer of trichloroethylene while granular I thermoplastic polymers to injection dispersed in water, said polymerimtion being car molding compositions such as by masticatingon a ried out at. a temperature oi’ 100° C.-150° C. under heated rolls or by --= w - 1 thrzmgh a screw stutter followed vby cooling and chopping to convenient autogenous ‘pressure. s FREDERICK L-JOHNSTON.