[1]United States Patent Office 3vO6l258O 3,061,580 UNSATURATED POLYESfE]f RFSINS CONTAINING A LITHIUM HALIDE AS STABIULIZER AND METHOD OF MAKING Warren 0. Erickson, Fort Lauderdale, Fla., and William J. Connolly, Toledo, Ohio, assignors to Allied Chemical Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Oct. 22, 1959, Ser. No. 847,906 13 Claims. (Cl. 260-45.4) This invention relates to resinousthermosettable polyester compositions that comprise copolymerizable inixtures of ethylenically unsaturated polyester resins and ethylenically unsaturated monomers. More particularly, the invention relates to the produc-tion of unsaturated polyester resin compositions that are exceptionally stable even at elevated temperatures and during long periods of storage prior to use, but which are nevertheless readily thermosettable subsequent to incorporation of catalyst into the mixtures. The term "unsaturated polyester resin compositiore' is used herein in the general sense it now conveys in the art; namely, to refer generally to those compositions that comprise a polymerizable unsaturated polycarboxylic acid-polyhydric alcohol polyester, which is prepared by an esterification reaction bet@veen on@- or more polybasic acids, at least one of which is unsaturated, and one or more polyhydric alcohols. Such compositions preferably comprise also acopolymerizable monomerir, substance that contains at least one CH2==C< group. In general, unsaturated polyester resin compositions of the type referred to cure or harden rather slowly. This characteristic originally limited the u-tility of such resins insofar as commercied use was concerned. However, it has been conventional in the art for some time to add a catalyst, usually some type of peroxy compound, prior to use of the polyester composition, wbereby the rate of thermosetting or cure is greatly increased. As a Tesult, polyester resin compositions have found wide applicability in the molding, laniinating, casting, coating, and other fields. Unfortunately, these polyester compositions, being thermosettable, begin to cure or harden either immediately upon mixing of the polyester and monomer components or shortly after preparation, even prior to the incorporation of catalyst, and the rapidity of this occurrence is increased by higher ambient tempcratures. Originally, this fact limited the use of these otherwise reeognizedly valuable materials to applications where they could be finally cured comparatively shortly after preparation. For the purpose of obvia-ting this serious limitation on the use of these compositions, it has also been conventional in tfie art for some time to incorporate in said compositions, certain substances known as gelatioln inhibitors or stabilizers, that prevent setting up of the compositions for appreciable lengths of time. Examples of polymeriza-tion inhibitors of commercial acceptability are hydroquinone, tertiary butyl-catechol, pbenzoquinone, 3- isopropyl ca-techol, 4-isopropyl catechoi and others. These inhibitors are normally employed in amounts effective to prevent premature gelation of a given polyester composition to a desired degree. A problem is posed by their use, since the inhibitory function against prema-ture gelation is carried over during the time Of cure in the presence of a catalyst. This results in either increased cure time or increased cost of additional catalyst if added to overcome said inhibito function. In the ry latter case, the additional catalyst may also ca-use difficultly controlled cures of the compositions. There are several criteria for determining the comparative worth or relative effectiveness of a gelation inhibitor. Patented Oct. -.3 1962 2, A primary criterion, of c-ourse, is the ability of the inhibitor to prevent gelation of the polyester resin composition in which i-t is incorporated, for "tended len 9ths ibf time under ordinary ambient temperature conditions. Another criterion is the ability Qf the inhibitor to function as such for shorter times under extraordinary temperature conditions prior to inclusion of peroxy catalyst. Finally, there is another criterion, most difficult of fulfillment, particularly in conjunction with the others, that 10 is the ability of the inhibitor not to interfere to any appreciable extent with the functioning of a peroxy catalyst that is incorporated in the resin compositions prior to ultimate cure. In the optimum situation, the ideal inhibitor functions not merely passively in the presence of 15- the added peroxy catalyst, but actively to -accelerate the aetion of the catalyst. Such compounds per se have come to be known as "promoters." There are similarly several criteria for deterinining the comparative worth or relative effectiveness of a com20 pound as a promoter for a peroxy catalyst system in polyester resin compositions. For example, the criteria relied upon in the standard Society of the Plastics Industry (SPI) hardening tests are useful for such comparisons. The tests are commonly referred to in group as the SPI 25 Gel Time Determination. Briefly, the tests involve determination of the time temperature characteristir-s of a particular resin sample solution containing a known amount of catalyst and a known amount of a particular 30 promoter. More particularly, one of these criteria determined in the aforesaid test is "gel tim4?' which is the time interval measured that it takes for -the resin sample solu-tion to pass from 150' F. to 190' F., wherein greater promotive power is reflected in shorter "gel time." Another criterion is "time of exotherm," which is the time, 35 interval measured from the time the sample attains atemperature of 150' F., until the highest or peak temperature is attained, the shortness of such time similarly indicating the degree of promotive power. StiU another 40 criterion is "peak exotherm," which is the actual highest temperature reached by the resin sample solution during cure. 'nis last value, in addition to indicating the promotive power of a substance used for such purpose, indicates the likelihood that the resin will cure to an ac45 ceptable rigid state under room temperature conditions and within a reasonabie time, the comparison, however, being taken under elevated temperature curing conditions. -- )O In addition to the foregoing, the room temperature pot life of polyester resin solutions containing predetermined amounts of catalyst and promoter is also of importance in determining the efficacy of a catalyst-promoter system. Pot life is measured as the time that it takes, subsequent to incorporation of the promotercatalyst system, for gelation to occur at room temperature, and 55 gelation is said to occur when the resin solution is no longer flowable. As a practical matter, it is necessary that a polyester resin have a sufficiently long pot life so that, after it is catalyzed and promoted by the additions of a peroxy compound and accelerator, respqctively, there 60 still remains sufficient time to pour, spread or otherwise arrange the resin into the shape or form desired in the hard6ned, rigid state, before it becomes non-flowable. On the other hand, it is frequently highly desirable, particularly in room temperature curing applir-ations, for the (;5 polyester resins to have a rather short pot life (e.g., is minutes) whereby gelation will occur very quickly after the aforesaid spreading or otherwise arranging operation, so as to eliminate flow-off, disarrange - ment, etc., which otherwise occurs and which usually requires time-consuming, continued spreading, reforming and rearranging 70 until gelation does finally set in. In certain applications, such as in the manufacture of
[2]3 button blanks, in the production of corrugated sheet, and the hke, it may be desirable to have the resin, that rontains the promoter-catalyst system, in a semi-cured gened condition for several hours after initial gelling to permit cutting or stamping of the products prior to rapid cure to an infusible state by post-curing thereof at an elevated temperature. Whffe certain of the presently known inhibitors that function dually as promoters for pdlyester resins after addition of peroxy catalyst do achieve optimum results in one or @more of the various criteria described above with respect to desirable inhibitive and promotive functions, they leave much to be desired in the matter of achieving desirabie balances""bf values in aU said criteria. The problem is complicated by the fact that, upon addition of many known inhibitorr. and/or promoters in polyester resins the substances per se tend to disoolor the compositions. Another known difficulty with the polyester compositions that contain a combined gelation inhibitor and promoter for peroxy-catalyst systems, is that while they may achieve varying degrees of fair or good results in the criteria discussed above, they may have the tendency to cause uncontrolled or run-away reactions due to the over. promotion of the peroxy catalyst. As a consequence, hot spots in localized areas of the curing mass may orcur with resultant serious flaws in the fmishe-d pro-ducts that are obtained therefrom. In view of the foregoing, it is a primary object of the present invention to provide polyester resin compositions that have improved high temperature and storage stability when in uncatalyzed state. -It is another object of this invention to permit the introduction of monomets to polyester resin oompositions even when the latter are at elevated temperatures, without inrurring undesirable premature gelation. -It is another primary object of the invention to pro. vide polyester resin compositions of the aforesaid stability when in uncatalyzed state, and w@hich have excellent gelation and curing characteristics subsequent to incorporation therein of peroxy catalyst. It is yet another object of the invention to provide such r,tabilized @polyester resin compositions that do not have their color affected adversely, even after curing in the presence of catalyst. It is yet another object of the invention to provide said stabilized polyester resin compositions that, when catalyzed, also provide optimum balances of various criteria for promotive effect; namely, gel time, time of exotherm, peak "otherm, pot life, and semi-cure life. Another object of the invention is to provide a method of stabilizing unsaturated polyester resin compositions that assures the aforesaidadvantages and, in addition, results in smooth and controfled polymerization reactions subsequent to addition of catalyst and application of curing conditions. It is yet another object of the invention to provide novel compositions that include two-component inhibitor systems that give improved inhibitive results and that, subsequent to incorporation therein of a peroxy catalyst, at least assure rapid, smooth, even, and controlled polym. erization and resultant minimization of flaws in the finally cured product, if they do not actuoy-enhance such curing results. Other objects, purposes and advantages of the invention will appear to those skilled in the art upon reading the description of the invention that follows. In general, the invention resides in methods of effectively stabilizing unsaturated polyester resins derived from polyhydric alcohol and unsaturated polycarbOxYlic acid, which comprises incorporating therein, as stabilizer, a lithium halide. The invention also comprises the production of polymerizable unsaturated polyester resin compositions that comprise (a) an esterification product of polyhydric alcohol and unsaturated polycarboxylic acid, 3,061,580 4 and (b) a lithium halide,,which compositions are exceptionaffy stable if stored for long periods of time in uncatalyzed state and for shorter periods of time at higher tem-peratures, but which are particularly adaptcd to be cured under desired conditions, by the addition of the peroxy catalyst chosen, such as benzoyl peroxide. It has been found that the lithium halide compounds described herein function in a completely unexpected manner as highly effective promoters for catalyst systems that in10 clude a tertiary hydroperoxide; e.g., cumene hydroperoxide. In a prefeffed embodiment of the invention, there is included the substance copper naphthenate, that has an unexpected synergistic effect on the stabilizing effect of 15 the lithium halide, and, subsequent t-) addition of peroxy catalyst, on the promotive effect of the lithium halide, even when said copper naphthenate is added in minute quantities. Preferably, in accordance with the invention, both in 20 exercising the methods and in the production of the prod. ucts, a compound containing at least one CHr-=C< group and having a boiling point above 60' C., and copolymerizable with the unsaturated polyester resin, is included. As polybasic r-omponent of the unsaturated polyester 25 resin, there may be chosen an alpha-beta unsaturated dibasic organic acid, of which are preferred maleic, fumaric, glutaconic, itaconic, mesaconic, and citraconic. Maleic, itaconic or citraconic anhydrides may be used instead of the corresponding acids. Other isomers of the maleic 30 series, -typified by allyl-malonic, allyl-succinic, and xeronic acids may also be used in the production of the poly. esters. Also employable are certain polybasic acids which decompose under heat to yield acids of the maleic type, such as malic and citric acids. Unsaturated dibasic or35 ganic acids admixed with other dibasic acids, such as phthalic, tetrachlorophthalic, hexachloroendomethylene tetrahydrophthalic (or their anhydrides), adipic, sebacic, etc., are similarly useful. The foregoing listing of acids with which polyesters may be prepared is to be under40 stood as merely ibustrative and not limitative, it merely being preferred that the polyester be an unsaturated polyester wherein at least 20 mol percent of the polycarboxylic acid is alpha-beta unsaturated polyearboxylic acid or anhydride. 45 Of the polyhydric alcobols which are known to be useful in the production of unsaturated polyester resins to which the present invention pertains, there may be chosen dihydric alcohols and mixtures thereof, or mixtures of dihydric alcohols and small amounts of higher r)o polyhydric alcohols. The glycols, such as diethylene giycol, triethylene glycol, trimethylene glycol, monoethylene glycol, and propylene glycol and derivatives thereof, may also be used. Examples of higher polyhydric alcohols whicb may be employed in the production 55 of the polyester c-ontemplated, in amounts not exceeding about 5 mol percent, are glycerol, pentaerythritol, man. nitol, etc. Also employable, as part or all of the dihydric alcohols to be used, are the more complex glycols of the bisphenol A type, such as those disclosed in U.S. Patent 60 No. 2,331,265. The unsaturated polyester resins for which the present invention has been found to be most useful are those that are manufactured from polyhydric alcohol and unsaturated polybasic acid by standard and well known 65 pt;lyesterific-ation techniques, to have acid numbers not greater than 50, although resins having acid numbers as high as 100 may be used and may even be desirable in some cases. Generafly, the acid number should be as as low as possibie, and particularly good results are ob70 tained when the I>olyester resin used has an acid numt>er between 15 and 50. A polymerizable unsaturated monomeric substance that may be included with the unsaturated polyester resins in conventional mariner and in the practice of the present 75 invention, may -be any substance (or raixture of such
[3]substances) whose molecule co@tains at least one polymerizable ethylenic double bond that is capable of copolymerizing with the polymerizable unsaturated polycarboxylic acid-polyhydric alcohol polyester. Examples of such monomeric substances are now well known in t:-e polyester art, and include, merely by way of example, styrene, 13-- methyl styrene, vinyl toluene, divinyl benzene, methyl acrylate, methyl methacrylate, acrolein, diallyl phthalate, triallyl cyanurate, the diallyl ester of endomethylene tetrahydrophthalic anhydride, etc. The catalyst that may be introduced into polyester resin compositions containing a lithium halide (and optionally, copper naphthenate), when cure of said compositions',is desired, may be any perc;xy catalyst such as benzoyl pe'roxide, tertiary butyl hydroperoxide, CYCIOhexanol peroxide, ascaridol, etc., or mixtures thereof. In the event the benefits of the promotive action of the lithium halide present in the compositions of the invention are also desireld, th6-peroxy catalyst system should comprise, at least in@ part tertiary hydroperoxide catalyst that may be a ' n aralkyl hydroperoxide having the following formula: I R2 Ri-@-0-@--OH where RI is an aryl group, R2 and R3 are alkyl groups and any of RI, R2 or R3 may contain substituents @!attached thereto, other than halogens or other atoms, or groups which might adversely affect the charadter of.@the hydroperoxide linkage. Examples of such,h@droperoiides are cumene hydioperoxide, cymene hydroperoxi4e, scebutylbenzene hydroperoxide, 1-methyltetralin hydroperoxide, etc. The compound to be used in conjunction with the polyester resin compositions to form the stabilized systems in accordance with the present invention is a lithium halide that is soluble in the polyester resin composition into which it is incorporated. The lithium halide may be incorporated in amounts ranging from about 0.0001% to about 0.5% by weight of the total polyester resin composition depending on the substance utilized, the kind and amount of @catalyst to be incorporated, and the extent of promoter action desired. For the purpose of greatiy augmenting the gelation inhibiting action of the lithium halide upon the unsaturated polyester resin system comprising copolymerizable polyester and monomer, it has been found advantageous in many instances, in accordance with the invention, to add a second specific composition. Thus, it has been discovered that the inclusion of even a minute amount of copper naphthenate augments the inhibiting action of the lithium halide on polymerization of polyes,ter resins to to a totally 'un6x;pected syneran unexpected degree, due gistic action, and moreover, eithei'does not affect the promotive function of -the hali4le or, depending on the peroxy catalyst chosen, enhaii6es the latter effect in a controlled manner, that av@"@o'ids run-away reactions and localized hot spots in,t hecuring mass. It has been found, that this second c.om@ound, copper naphthenate, may be included in amounts from about 0.0001 % to about 0.5 % by weight of ihe total polyester composition to perform its functions. When appreciably less than the aforesaid minimum amount is included, no practical effect is observed, whereas when appreciably more than the maximum amount of sec-ond compound is employed, the stabilizing function of the lithium halide is not additionally affected to an extent that from a practical standpoint, warrants any greater amount of copper naphthenate than said maximum. The inclusion of copper nap4thenate as compound that functions as second inhibiter arid, under certain circumstances, as second promoter, in addition to permitting controlled curing of the compositions subsequent to introduction of catalyst, whereby more uniform gel times are achiived with similar compositions; also 3,001,580 6 decreases the obs-ervable gel time to a marked degme. In the exercising of the invention, the unsaturated polyester chosen to be used is preferably mixed with a monomer, as referred to above; and a lithium halide. When desired, copper naphthenate as second inhibitor is also thoroughly mixed into the polyester-monomer mixture. This results in the highly desirable benefits of the invention, whereby the polymerizable compositions are rendered high temperatur46- and storage-stable. 10 Thereafter, which may be months later, and at a predetermined time before the ultimate use of the unsaturated polyester composition for curing, the peroxy compound chosen is incorporated as catalyst. The predet@rmined time is dependent upon the prop6rtions of ingredients 15 employed chosen for a particular application, since sufficient time is allowed by the use of the novel inhibitorpromoter system described herein, to permit placement of the polyester composition where it is intended to be cured. The following typical formulations are given by way of 20 example to iilustrate the methods and compositions of this invention. AU parts are given by weight. EXAMPLE 1 An unsaturated polyester resin was prepared in conven 25 tional manner from components consistin-. of 0.17 mol phthalic anhydride, 0.38 mol maleic anhydride and 0.52 mol dipropyiene glycol, by heating a mixture@ thereof. The heating was carried out under a C02 atm6sphere at an elevated temperature for a period of time' until the 30 acid number had fallen to appreciably below 100, as is conventional in the art. Thereafter, styrene and hydroquinone were added to the polyester in ainounts that were 26% and 0.013%, respectively, of the total composition. Three equal batches of the final polyester resin 35 cornposition were then separated and designated as samples "A," "B" and "C." Into said samples designated "A" and "B," amounts of lithium chloride were charged to the extent of 0.005% 40 and 0.010% of the total weights of said samples, respectively. No lithium chloride was introduced into sample "C," that was intended to function as a control. Equal portions of each of said three uncatalyzed samples were then tested for stability at high temperatures by maintaining the sample portibns at 120' C. and observing the time 45 interval for gelaii6n to occur. The remaining portions of each of the thrie samples "A," "B" and "C' were then catalyzed by introduction of an amount of benzoyl peroxide so that said catalyst was present in each sample in amount that equalled 1.0% of eacb, respectively. 50 'fbereafter, equal parts of the catalyzed samples "A "B" and "C," respectively were placed in an oil bath at 180' F., and the "SPI Gel Time," the "Peak Exotherm Temperature" and the "Time to Peak Exotherm" were observed (i.e., the time it takes for the temperature of the 55 sample to rise from 150' F. to 190' F., thd highest temperature attained by the sample, and the time interval for the last temperature to be reached, respectively, as referred to hereinbefore). The results of the foregoing observations are given in Table I, below: fjo Table I Stability Peak Time to Sampl e at 1201 C. Gel Time Exotberm, Peak (Minutes ) F. Exotb erm 65 C (Control) --------- 20-M 5 Min ------- 406 6 min., 24 we A --------- --------- 130- 190 5 Min., 22 395 @ min'. We. B --------- --------- 240- 260 a Min., 22 402 7 min. see. 70 EXAMPLE 2 Another unsaturated polyester resin was prepared in conventional manner from components consisting of 0.29 75 mol maleic anhydride, 0.22, mol isophthalic acid, and
[4]7 0.50 mol diethylene glycol, by heating a mixture thereof. The heating was carried out conventionally under an inert atmosphere at an elevated temperature for a period of time until the acid number of this polyester,had fallen appreciably below 100. Thereafter, styrene and hydroquinone were added to the polyester in amounts that were 30% and 0.004% of the total composition. As in Example 1, three equal batches of the polyester were separated and then designated, in this case, as samples "D," "F' and "F." Into samples "D" and "E," amounts of lithium chloride were charged to the extent of 0.001 % and 0.005 % of the total weights of said samples, respectively. As in Example 1, no lithium chloride was introduced into the third sample "F,' that was intended to function as a control. Equal portions of the three uneatalyzed samples"'D," "E" and "F' were tested for high temperature stability and for slightly elevated temperature stability by observing the time intervals necessary for separate samples to gel when maintained at a temperature of 120' C. and at a temperature of 120' F., respectively. Other portions of the three samples '@D," "F' and "F" were catalyzed by introdur-tion of benzoyl peroxide so that the amount in each sample equalled 1.0% of each, respectively. Equal portions of the catalyzed samples "D," "E" and "F," respectively, were then placed in an oil bath at 180' F. and the "SPI Gel Time," "Peak Exotherm," and "Time to Peak Exotherni" were observed as in Example 1. The room temperature pot life of each of these samples was also observed. Such observation is done simply by introducing 80 grams of each of the three resin samples into 150 ml. beakers and allowing them to set at room temperature. The samples are checked frequently and the pot life of each measured as the time that it takes for gelation to occur. The results of all of the foregoing observations are given in Table 11, below: Table If Sample F Sample D Sample B (Control) Stability at 1201 C. (Minutes)- 2D-40 -------- 70 - --------- 120-190. Stability at 1200 F. (Days) --- - 6 ------------ 40 ----------- 47. Gel Time --------------------- 3 min., 24 3 min., 37 4 min., 7 sec. see. Sec. Peak Exotherm 406, F 4321 F 4091 F --- 14min.- ---I 5m -ii , ii 30 'nme to Peak 4 min., se@., sm. c Pot Life (Days) -------------- 2-3 ---------- I 2-s3ee i. -th. I It was also observed that when lithium chloride is added at an elevated temperature of 110' F. to the uncut base resins such as those described in Examples I and 2, it furnishes exceuent stability by avoiding gelation during the addition of monomer, in addition to giving extended room temperature shelf life. JEXAMPLE 3 A polyester was prepared from components comprising 0.25 mol phthalic anhydride, 0.25 mol maleic anhydride, and 0.52 mol propylene glycol, by conventionally heatreacting the same under an atmosphere of C02 for an extended period of time until the acid number was appreciably below 100. Styrene and hydroquinone were admixed with the resulting polyester in proportions that the monomer and inhibitor comprised 34.5 % and 0.003 respectively, of the total composition. In a batch of the - above-described polyester-monomer resin composition, there was charged lithium chloride to the extent of 0.01% of the total weight of said batch. Two equal portions of the batch were designated "G" and "H," and in sample "G," there was included copper naphthenate in amount that was 0.0006% of the total weight of the sample. Portions of both of the samples "G" and "W' were subjected to the 120' C. stability test, 8,061,580 8 and other equal portions of said samples were catalyzed by introduction of benzoyl peroxide therein to the extent of 1% of the total sample, and the "SPI Gel Time," "Peak Exotherm Temperature," and "Time to Peak Exotherm," were observed as in the previous examples. The results of the foregoing observations are given in Table IH, below: Table III 10 Stability SPI Gel Peak Ex- Time to Polyester Resln Sample at 1201 C. Time otherm, Peak Ex (min- (Min- F. otlaerm, utes) utes) minutes Ctg..010% Lici---- H....... 45 5% 392 7.1 15 ctg. 0.10% LiCl+ 0.0,106% Ca Napbth --------- G------- 75 SHI 392 7.1 It was found that the copper - naphthenate in sample 20 "G," that obviously increased the uncatalyzed shelf life of the polyester resin in which it was incorporated in conjunction with a lithium halide, had no undesirable effect on the curing characteristics of the compositions after introduction of catalyst nor on the color of the cured 25 products resulting therefrom. It is to be understood that the constituents of the polyester compositions in the foregoing examples have been selected as representative of the materials normally found in such compositions, and that the advantages obtained 30 by the invention are unaffected by convenfional substitutions or omissions. For instance, similar results are obtained ff the styrene is replaced in whole or part by methyl methacrylate or other known cross-linking monomer. Incorporation of glass fibers in the resin composi35 tions, and/or otlier fibers, such as asbestos fibers and the like, may be accomplished before or after the inclusion of peroxy catalyst if the compositions are to be used in molding applications, for extrusions, or in laminating operations, for example. Similarly, other filler materials 40 may be included, additional stabiezer may be omitted, and/or other conventional stabilizers, pigments and other additions may be added or substituted for those disclosed. Furthermore, the relative proportions of the constituents listed in the examples or the substitutes therefor list45 ed in the foregoing paragraph, as well as hereinbefore, and/or known in the polyester resin art, may be varied within very wide limits. Thus the unsaturated polyester resin constituents can be varied, and the proportion of m onomer-polyester resin in the unsaturated polyester 5o combination may likewise vary between very wide limits. Moreover, the proportions of stabilizers, promoters, and catalysts can be varied to give the desired combination of shelf life and high temperature stability when in uncatalyzed condition; and pot Iffe, as well as gel time, semi55 cure life, and cure time characteristics, when in catalyzed condition. We
