Condensation of Phenols with 111. Direct Formaldehyde
Resinification
F. 5 . GRANGER 50 East 41st Street, New York, N . Y.
N PREVIOUS articles of this series (4, 6) the formation of resins by reaction of phenols with formaldehyde has, for convenience, been considered in two stages-the formation of phenol alcohols followed by condensation of the latter to form resins. For industrial purposes, however, it has not been customary to separate these two reaction stages. Instead, a mixture of the phenol with formaldehyde (as the approximately 40 per cent formalin solution) is subjected immediately to resinification conditions. In that case the intermediate formation of phenol alcohols is followed without interruption by their condeneation to resinous products with more or less rapidity, depending on reaction conditions, and is lost sight of , therefore.
I
Direct os. Phenol Alcohol Resinification
This article covers the additional fundamental factors arising when the successive combination and condensation reactions involved in the formation of phenol formaldehyde resins are combined in a single operation, as in industrial practice. The contrasting characteristics of alkaline and acid condensations are discussed and illustrated by experimental data.
the xylenols and higher homologs, the solubility in formalin is limited, decreasing as the series is ascended. It increases with temperature, however, reaching equimolarity in some cases. Thus highly concentrated homogeneous reaction mixtures with the simplest phenols can be prepared containing any desired ratio of reactants. More moderate concentrations, however, down to the low solubility of these phenols in water alone, except with increasing excesses of formaldehyde, are excluded by the limitations of the solvent effect of formaldehyde. With the higher phenols the possibilities are increasingly limited. Solubility of phenol alcohols in water varies greatly with different individuals, generally decreasing as the molecular complexity of the parent phenol increases and increasing with the ratio of formaldehyde to phenol. Probably only in the case of the polyalcohols of phenol are concentrations comparable to those of phenol-formalin mixtures approached, but there are no limits to dilution. With the higher monohydric phenols, whether uncombined or as phenol alcohols, we must usually resort to phenolate conditions or to organic solvents for homogeneous reaction mixtures a t practical concentrations. condensation may be effected in heterogeneous mixtures, but this is usually less satisfactory.
The contrasting characteristics of acid and alkaline conditionw, as applied to the resinification of phenol alcohols (6), also apply here. I n direct condensation, however, additional factors are introduced, modifying the situation in certain respects and giving rise to a further differentiation between acid and alkaline conditions which involves questions of considerable practical importance. This differentiation lies principally in the respective effects of these conditions on the relative velocities of combination and subsequent condensation and on the ratio of combination. The latter is a curability-determining factor which does not enter into the simple resinification of phenol alcohols, in which the ratio of combination is already fixed. The proportions in which the phenol and formaldehyde combine are seldom the same as thesproportions in the reaction mixture. Consequently in direct condensation the initial combination or phenol alcohol formation, which occurs mainly before resinification under alkaline conditions, and simultaneously with it under acid conditions, leaves free an excess of phenol or formaldehyde or both, in the presence of which the subsequent resinification occurs. Direct and phenol alcohol resinification differ also with respect to concentration ranges, as determined by solubility Alkaline Condensation relations. Only the common case where the inert solvent Under alkaline conditions resinification of phenol alcohols vehicle is water is considered here, and obviously phenolate is considerably slower than their formation, especially in the Conditions are excepted. Under nearly neutral or acid conditions the situation is as follows: I n direct resinification recase of equimolar mixtures. I n that case these two stages of reaction, in direct condensation, overlap only to B slight exaction mixtures the usual initial solvent is the aqueous solutent and are easily distinguished. With higher formaldehyde tion known as formalin, containing about 38 per cent by ratios a longer time is required for complete combination, and weight of formaldehyde, in one form or another. Monohydric resinification is more rapid, resulting in considerable overlapphenols are much more soluble in this solution than either ping. they or most of the phenol alcohols are in water alone. Phenol and the cresols are miscible with formalin in all A further differentiation from acid condensation is found in the ratio of combination. From reaction mixtures of the proportions but differ in that only phenol will tolerate much dilution with water without precipitation. This toleration same proportions, phenols take up more formaldehyde under is decidedly increased by slight alkalinity, however. With alkaline than under acid conditions. Thus, with equimolar 1125
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INDUSTRIAL AND ENGINEERING CHEMISTRY
mixtures and phenols capable of combining with more than an equimolar proportion of formaldehyde, more than an equimolar proportion is actually utilized in the initial combinatioc'under alkaline conditions, as will be shown, leaving considerable free phenol. The latter is taken up in the subsequent resinification but usually incompletely. The degree of curability is correspondingly affected ( I ) , according to the type of phenol (6). Thus, with phenol or m-cresol (type 3), equimolar as well as higher proportioqs of formaldehyde yield highly curable resins. The indifference of resinification velocity to the degree of alkalinity, its variation with different phenols and formaldehyde t o phenol ratios: and other characteristics manifested in the alkaline resinification of isolated phenol alcohols (6) also apply here. Alkaline conditions are of two types according to the degree of alkalinity. Strong alkalinity functions dually, as solvent as well as catalyst; in the usual weakly alkaline processes ( I ) , essentially only the catalytic function is employed.
Base as Solvent and Catalyst (Phenolate Conditions)
.
The former condition exists when the proportions of a strong alkali to the phenol are varied from more than equimolar down to about one-fifth that amount in aqueous solution. The resin, because of its phenolic properties, usually remains held in the aqueous solution by the alkali and may be precipitated by neutralization a t the desired stage of condensation. Processes of this type have appeared in the patent literature (6). They constitute a convenient means of maintaining homogeneous &action mixtures for a wide range of phenols and concentrations, and of producing a resin, especially a curable resin, in powder form and definite chemical state. When an equimolar reaction mixture of this type is boiled under reflux, phenol alcohol formation is completed in the fist few minutes, as shown by the disappearance of the formaldehyde odbr, a minor portion of which is consumed a t the same time by Cannizzaro's reaction (5). Very litt.le resinification occurs during this short initial period. From this point on, therefore, the process is simply the resinification of phenol alcohols (@, except for the presence of residual free phenol in the case of phenols of type 2 or 3, mentioned above as applying to direct alkaline condensation generally. The presence of this free phenol, together with the compensating polyalcohols, and its subsequent incomplete participation in the resin-forming condensation do not materially modify the snecific Dhenolate procem characteristics which were described preGously (5).The small portion not eventualiy utilized is usually lost in the subsequent processing, filtration, etc. The net result is merely a somewhat higher ultimate carbon (CHzO-H%O) content and consequent curability than would result from the resinification of minoalcohols alone. With higher formaldehyde ratios up to the limit with which the phenol will combine, complete combination requires a longer time which may extend well into the resinification stage. The result is that more formaldehyde is lost by Cannizzaro's reaction but more is also taken up, with a corresponding increase in curability. Also the resinification velocity in*creases rapidly with the ratio of formaldehyde to phenol, within the above limit.
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Base for Catalysis Only I n this category the conditions substantially as covered by the early, well-known Baekeland process ( I ) are contemplated by the writer. These comprise weak bases generally or smaU
VOL. 29, NO. 10
proportions of a strong alkali. In this case, the solvent effect is unimportant althoughit may not be entirely absent. Chemically the results appear to be similar to those under phenolate conditions, but the physical behavior and resulting practical aspects are quite different. Assuming the alkalinity to be such that its solvent effect is negligible, the resin, in the earlier stages of its formation, is held in solution by the solvent effect of the remaining phenol alcohols. Precipitation starts when the increasing concentration of the resin exceeds the solvent effect of the decreasing concentration of phenol alcohols. The resin precipitates in liquid form, probably carrying down phenol alcohols with it to some extent. But it gradually solidifies in the hot mixture as it accumulates, while the resinification of the remaining phenol alcohols continues in both phases. I n the case of highly curable or Bakelite-type resins, such as are obtained from phenol or m-cresol, this introduces another complication-namely, curing during resinification. Under phenolate conditions curing may occur if the heating is unduly prolonged. Usually, however, it occurs only after resinification of the phenol alcohols is almost complete because curing is generally much slower in solution. At resinification temperatures around 100" C. resins of this type (out of solution) cure fairly rapidly, although much more slow$ (especially with reference to the C stage) than a t the higher temperatures (e. g., 180" C.) used in molding. Therefore, in the present case the precipitated resin, if of the highly curable type, cures to a substantial extent while the initial resinification is still in progress.
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FIQURE 1. ANALYSISOF A CONDENSATION OF PHENOL EQUIMOLAR QUANTITY OF FORMALIN CATAONE-TWENTIETH ITSEQUIVALENT OF NORMAL SODIUM HYDROXIDE
WITH AN L Y Z ~ DBY
Consumption of formaldehyde complete at a; precipitation of resin begins a t b.
In industrial practice some point must be selected a t which the process is to be stopped. It is therefore of practical interest to know the condition or composition of such a reaction mixture a t various stages. This is shown continuously in Figure 1 which illustrates quantitatively the various characteristics of alkaline condensation that have been mentioned. It was derived experimentally as follows: Reaction mixtures were made up of equimolar quantities of pure anhydrous phenol and a formaldehyde solution (39 grams per 100 cc.) with the addition of a 0.05 molar quantity of normal sodium hydroxide solution. The mixtures were heated under reflux for various lengths of time in a boiling 20 per cent brine bath and then analyzed as described below. The results were calculated as percentages accounted for of the original phenol. As with the phenolate method, the odor of formaldehyde was barely perceptible after 15 minutes of heating and had disappeared entirely in a half-hour. The mixtures remained homogeneous during heating for periods varying from 2.5 to
OCTOBER, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
3 hours. On continued heating, precipitation ensued. It appeared to be liquid a t first and increased rapidly, collecting at the bottom as a white elastic cake. The persistence of homogeneity, until the greater part of the ultimate resinification had taken place, showed the solvent effect of the phenol alcohols, etc., on the resin. As the resin precipitated, it cured rapidly a t the reaction temperature, as shown.
Analytical Procedure The method of analysis differed according to the stage at which the condensation was stopped. When the heating was stopped before precipitation had occurred, the bulk of the resin precipitated on dilution, except in the very early stages. The precipitation was completed on neutralization with hydrochloric acid. The precipitates were liquid or plastic. They were dissolved in sodium hydroxide solution and reprecipitated by neutralization several times to remove phenol alcohols, etc. After washing, they were dried and finally dehydrated at 185' C. to constant weight to obtain a definite basis for calculation. This treatment converted them to the C state. The filtrates and washings from the resins contained the phenol alcohols and unreacted phenol. They were distilled down to a small volume, and the residue was steam-distilled to remove the Dhenol completely. Phenol was determined by the improved Koppeschaai method (14). The henol alcohols were artly resinified during the distilladetermine them. t i e resinification was comdeted bv tion. heating the distillation residues with hydrochloric acid. Thk resins so obtained were filtered off, washed, dehydrated to constant weight, and ashed. In the case of the condensations which were carried into the precipitation stage, a tough elastic cake, corresponding in pro erties to Bakelite B, was formed. After decantation, this cafe was soaked in alcohol until disintegrated to a white powder which was filtered off and washed with alcohol. The insoluble residue (designated "resinoid" in Figure 1) was heated at about 185" C. to constant weight. The decanted water and the alcoholic filtrate were combined, diluted with water, and neutralized. The alcohol was then removed by distillation, causing the highly curable resin to precipitate. The alcoholic distillate was refractionated to recover any phenol carried over with it. The rest of the analysis was carried out as already described.
80
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Calculations I n order to place the results on an equivalent basis, for plotting, they were all calculated back to percentage of original accounted-for phenol. To accomplish this, the molar ratio of formaldehyde to phenol entering the composition of the resin was estimated from the almost complete 8-hour condensation, and was found to be close to 11/10. Therefore, on the experimentally justified assumption that ultimate dehydration (6) amounts to 1 mole of water per mole of formaldehyde, the factor 0.877 was obtained for converting dehydrated original resin and resinoid into equivalent phenol. The formaldehyde thus accounted for was deducted from the total, and the remainder was assigned to the phenol alcohols. T o obtain the phenol equivalent to these, the weight of one atom of carbon (CHz0-HZO) per molecule of formaldehyde was deducted from the weight of dehydrated resin obtained in the determination of the phenol alcohols, as described.
Discussion of Results During the first 15 minutes, the period in which practically all of the formaldehyde was taken up, hardly any resinification occurred. Since only a little more than half of the phenol was consumed in this stage, the phenol alcohols formed must have consisted largely of polyalcohols. As condensation proceeded, a further quantity of phenol was taken up in the formation of the resins (roughly in proportion to the consumption of phenol alcohols) leaving ultimately about 10 per cent of the original phenol permanently free, after resinification was complete.
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The molar ratios of formaldehyde to phenol for the phenol alcohols remaining after the various stages of condensation, as calculated from the results, were as follows: Hours
Ratio
0.25 1.72
1 1.59
2 1.64
3 1.71
4 1.04
5 1.41
8 1.61
The ratio of formaldehyde to phenol incorporated in the final resin, although less than in the phenol alcohols, was still in excess of equimolar, resulting in high curability (1). Curing a t this temperature approached a constant value short of complete conversion of the resin to insoluble resinoid. Possibly this condition corresponds to the B state. After extraction of the resin, etc., from the precipitated cake, the residual insoluble resinoid wm deficient in thermoplasticity under molding conditions, to a degree indicating that it was already largely in the C state. The following features of the above results are illustrative of general characteristics of direct alkaline condensation: 1. The ratio of formaldehyde to phenol entering into phenol alcohol formation, much higher than the equimolar ratio of the reaction mixture. 2. The entrance of the residual phenol into the subsequent resin formation. 3. The difference in velocity between phenol alcohol formation and resinification, permitting the two stages to be easily distinguished. 4. Resinification approaching completion in the same time as under phenolate conditions, with twenty times the proportion of alkali.
Increasing the Formaldehyde I n any alkaline condensation it naturally takes longer for a mole of phenol to combine with 2 moles of formaldehyde than with 1 mole. On the other hand, speed of resinification of the alcohols increases with the proportion of formaldehyde. The result is a decided overlapping of the two stages, accompanying the reduction in the time required for condensation. When a reaction mixture containing 2 moles of formaldehyde to 1 mole of phenol and 0.05 mole of sodium hydroxide was made and heated as described, the disappearance of the aldehyde odor was so gradual that it was impossible to ascertain when it was complete. I n the meantime, extensive resin%cation occurred. Precipitation began a t 70 minutes (as compared to more than double that time with the equimolar mixtures), and the odor of formaldehyde was still perceptible though faint. On cooling, diluting, and neutralizing the mixture a t this stage, the resin precipitated in a pure white, granular form. It was conyerted to the B state, without alteration of appearance, by heating in a vacuum oven for 3 hours at 80" C. The yield was then 115 grams per mole of original phenol (94 grams). The theoretical yield, with complete dehydration, would be 118 grams. It gave excellent molding results a t 185" C.
p-Cresol The behavior of the type 2 phenol, p-cresol, on residication with an equimolar quantity of formaldehyde under the above conditions, was as follows: Precipitation of resin from the homogeneous reaction mixture started after 1 hour of heating and increased to a copious, white, mushy solid during 25 minutes of further heating. The percentage composition of the reaction mixture a t this stage, in terms of original cresol, was as follows: Formaldehyde utilized Cresol uncombined As cresol alcohols As resin
96.6 11.7 10.9 77.4
The resin was 30 per cent insoluble in acetone after drying in a vacuum for 8 hours a t 80" C. The uncured portion, like
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1128
all p-cresol resins, formed a homogeneous varnish on heating with China wood oil and thinning with Sunoco Spirits.
Acid Condensation When phenols are condensed directly with formaldehyde under acid conditions to form resins, the two stages, combination and condensation, are not distinguishable as they are under alkaline conditions. This is probably because resinification of phenol alcohols is faster, as compared to their formation, under acid than under alkaline conditions. Phenol alcohols have been isolated, however, from the early stages of direct acid condensation by de Laire (10) and by Gotthelf for Baekeland (a), but they evidently do not accumulate. Acid resinification is further characterized by its decided and continuous increase in velocity with increasing concentrations of reactants or catalyst (hydrogen ion). This has been discussed in copnection with the resinification of phenol alcohols (6) and applies also to direct resinification. Because of the higher concentrations involved in the latter case, we find a more striking manifestation of the highly exothermic nature of the reaction and its tendency to become violent at high concentrations. Kleeberg (8) was probably the first to observe the effect of acidification on a solution of phenol in formalin. With a formaldehyde ratio in excess of 2 molecules to 1 of phenol, the solution was strongly acidified with hydrochloric acid a t room temperature. Even with artificial cooling, the temperature rose rapidly to the boiling point, while a rose-red viscous mass separated and solidified to a hard sponge-like cake. The product a t this stage was evidently already highly cured since it dissolved only in traces in the usual solvents and, on heating, charred without melting. These results were confirmed and extended to other phenols by Hosaeus (7), referring to unpublished work of Tollens, and by Brissonet (3). I n a group of subsequent patents (16) an effort was made to utilize the acid resinification method by various modifications, complications, and limitations. Pollak (11) and Baekeland (I), referring to the work of his assistant, Thurlow, showed that the reaction could be easily controlled by merely limiting the degree of acidification sufficiently. The differentiation between acid and alkaline condensation, with respect to the ratio of combination, was also brought out by Baekeland (I). From an approximately equimolar reaction mixture, under acid in contrast to alkaline conditions, Less than an equimolar quantity of formaldehyde is utilized and consequently the resinous product is mainly Novolak. Sufficient excess of formaldehyde, however, as in the experiment of Kleeberg (8),will yield a highly curable resin. The various characteristics of direct acid condensation are illustrated in further detail and continuity in the following experimental observations of the writer: Homogeneous mixtures of 10 grams of phenol with approximately 40 per cent a ueous formaldehyde solution (formalin), in the roportions inzicated below, were resinified by adding 5 cc. o f concentrated hydrochloric acid at room temperature. The calorific effect or violence of the reaction diminished as the pro ortion of formalin was increased. This was attributable to t i e diluting effect of the latter. Excessive heating was avoided by external cooling. Samples of the resulting resins were extracted with acetone before and after a half-hour curing test at 180° t o 190°
c.:
Molar ratio taken HCHO/CaH,OH Soluble before curjng, % Soluble after curing, % Novolak % Curable 'but uncured, before test, % Cured bkfore test, % Total curable, %
1.0 86.0 64.6 84.5 20.6 15.0 35.6
1.33 47.5 8.3 8 3 39.2 52.5 91.7
2.0 35.8 6.0 6.0 29.8 64.2 94.0
To produce a completely curable resin under direct acid conditions, a large excess of formaldehyde is required, much of which is wasted. Under alkaline conditions only the minimum
VOL. 29, NO. 10
quantity of formaldehyde is required and practically none is wasted. When the reaction was moderated by dilution to permit temperature observations, it was found that the heating effect occurred in two stages. There was a gradual temperature rise from the start, during which the precipitation of resin was apparently completed. It separated out as a semitransparent viscous liquid. The reaction then subsided for a while, and the mixture started to cool. Then the second stage started rather suddenly with a greater heating effect than the first. The resin shrank somewhat and became thicker and opaque. The eventual solidification and development of the pink color (associated with curability, under acid conditions, 6) followed gradually. The effect of varying proportions and dilution is illustrated by the following data, based on 10 grams of phenol, to which 8 cc. of formalin is approximately equimolar: Formalin
Acid
Go.
cc.
8 S
2 5 4.6 2 4 5 9
10.5 15 15 15 16 16
2
Water
Product
Reaction
0 0 0 0 0 0
Novolak 64.57 Novolak 91.7& curable Partly curable B state in 12 daya, cold B state in 2 days, cold Kleeberg produot Novolak
Mild Violent Violent Mild Mild Moderate Very violent Mild
cc.
0 25
In this connection it should be noted that the calorific effect is influenced also by the scale of operations. Thus a reaction may be quite moderate with quantities of the above order and violent when the scale is increased, say, ten times. This is because the rate of heat escape from the system, being a surface function, increases only as the two-thirds power of the volume. The above results are therefore to be taken only in a comparative sense. It is apparent that the type of product obtained, with respect to curability, depends not only on the ratio of formaldehyde to phenol in the reaction mixture, but also on the intensity or velocity of the reaction as determined by the degree of acidification and concentration. These, therefore, probably influence the proportion of formaldehyde utilized. m-Cresol (10.8 grams = 0.1 mole) and formalin (15 cc. = 0.2 mole) with 1 cc. of hydrochloric acid, gave a reaction that was over i? 18 minutes. The product was similar to Bakelite A as defined in the literature (1). With 2 cc. of acid the reaction was over in 6 minutes and the product changed from the A to the B state on standing. The pink discoloration was much slower in developing and less pronounced than with phenol, but the brown discoloration, developing gradually in the C state after molding, was about the same. With equimolar proportions m-cresol yielded a permanently white Novolak. In all cases, good yields were obtained and good molding results, when the products were mainly of the highly curable type. Phenols of types 2 and 1 also yielded pure white Novolaks by this method, which is therefore advantageous when this type of resin is desired. These resins showed a little yellow or green color after melting to dry and clarify them. A specimen of the oil-soluble p-cresol Novolak, which was allowed t o dry in powder form without melting, has remained pure white for six years. This resin makes an excellent varnish.
Correlation of Direct Condensation Characteristics Referring to direct condensation in general there is a possible correlation between the ratio of combination and the relation of the velocity of resinification to that of initial combination to form phenol alcohols. This correlation requires the presupposition that formaldehyde molecules do not attach themselves as readily to the nuclei of a resin chain as to a free phenol molecule.
OCTOBER, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
The resin chain molecule is formed by condensation of phenol alcohol molecules with themselves and also with freephenol molecules when these are present. Under alkaline conditions the initial combination between the phenol and formaldehyde takes place more readily than the resinscation of the resulting phenol alcohols. The result is that a larger proportion of the available formaldehyde has entered into combination with the phenol before chain condensation than under acid conditions, where the reverse appears to be the case. Therefore, if the above presupposition is correct, a larger proportion of formaldehyde must enter into the resin molecule in the former than in the latter case.
Low Formaldehyde Ratios For ratios of formaldehyde to phenol less than equimolar, the general condensation equation may he written empirically as follows:
+ (n-1)
nCaHsOH
ZC&OH
ter case ammonia is liberated in the condensation instead of water. Pollak and Riesenfeld (I9) used the former method for the preparation and formulation of 5 Novolak of definite composition. This work is closely related to that of Koebner and to experiments of the writer ( 5 ) . From 25 grams of polyoxymethylene and 94 grams of phenol (CHsO :CsH,OH = approximately 5 : 6 ) the quantities of water formed and reactants consumed and the elementary composition of the resinous product indicated the formula: 7CaHsOH
Literature Cited
+
+ CX,O --+C,,H,,O, + H1O + CaHsOH --+C,r&~O*+ Ha0
or HOCsH..CHpOH
Conceivably, C,aH,,O, may he either HOCsHI-CH&H,OH or HOC~H,.CHSOC~&. In the case of phenol, even under acid conditions which favor a higher phenol to formaldehyde ratio of combination than alkaline conditions, Koehner (9)found that progressively increasing excesses of phenol are required in the reaction mixture, in approaching the minimum combination ratio of formaldehyde to phenol. The two extremes of the series of ratios tried by Koebner in condensing reaction mixtures of phenol, p-formaldehyde, and hydrochloric acid, yielding Novolak resins, gave the following results: From a reaction mixture ratio of 7 moles of formaldehyde to 10 of phenol the composition and yield of purified product were near the theoretical for 5CHsO G C B I ~ O H - ~ H ~ O
+
i. e., a ratio of SI/, to 10, while the minimum combination ratio of 1 to 2 was not quite reached even with a reaction mixture of 1mole of formaldehyde to 10 of phenol. This reversal of what is found on the other side of the equimolar ratio is probably due to resistance to shortening of the molecular chain in the case of some phenols or simultaneous formation of longer chains. Certain other phenols, on the other hand, representing the opposite extreme, form the diphenolmethane even under alkaline conditions and in the presence of a large excess of formaldehyde (4). The work of Koebner will be cited more fully in a future articlein connectionwith thesubject of structural formulation.
Dry Condensations Effective condensations are obtained without solvent hetween phenols and derivatives of formaldehyde in which an acid or basic substance has been taken up in a previous reaction. Thus, the formaldehyde equivalent carries in its own composition what might be called a “potential” catalyst. Outstanding examples of this class are the well-known processes of Pollak (12), using @-polyoxymethylene (a sulfuric ester of a polyoxymethylene hydrate, I 7 ) , and Redman, Weith, and Brock (15), using hexamethylenetetramine. In the lat-
+ 6CHzO -6HzO
Closely agreeing molecular weight determinations, however, by two different methods, indicated five nuclei instead of seven. This discrepancy was attributed to loosely hound terminal links.
CH*O +CY._~HB.O, (n-1) Ha0
The ratio (n-1) to n decreases with the value of 1z. This means that decreasing the ratio of combination involves shortening the resin molecular chain. Theoretically and actually the minimum ratio of formaldehyde to phenol entering a condensstion product composition is 1 to 2. This also represents the simplest condensation product or shortest chain:
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(7) (8) (9) (10j (11) (12) (13) (14) (15) (16)
(17)
Baekeland, 3. IND.ENNO. CHEM..1,149,5415 (1909): U. S. Patent 942,809 (1909). Beekelend, J. IND.ENG.CHEM.,4, 739 (1912). Bpiwnct. British Petent 5650 (1899). Granger, IND.Em. CBEM.,7.4,442 (1932). Ilvid., 29. 860 (1937). Hentsohke, German Patents 157.553 and 157,554 (1903); Steohan. U. S. Patent 812.608 (1906): Bhamst. IM.. 1,9&3,4tib (1934). Hosaeus, Ber., 25, 3213 (1892). Kleeberg, Ann.. 263, 283 (1891). Koebner. Z. aweu). Chem.. 46. 253 (1933) Lairs, di, fi&h Patent %61,539(1905): Pollsk. Germen Patent 263,109 (1909). 15s.. 310,894 (1911). Pollak and Riwenfeld, 2. angeu). Chem.. 43, 1129 (1930) Redman, Weith, and Brook, IND.ENQ.CHBM., 5,389 (1913). Redman. Weith, and Brock, Ibid.. 6, 3 (1914). Smith, British Patent 16,247 (1899): Blumer. Ibid., 12,880 (1902): I d t , Ihid., 10,218 (1902); Fayolle, Frenoh Patent 335.584 (1903): Serason, German Patent 219,570 (1905); Grognot, French Patents 390,713 and 392,978 (1907); Gentsoh. Ibid.. 384.425 (1907): Lebaoh. British Patent 28,009 (19On; Xildebrsndt. U. S. Patent 876.311 (1908). Staudinger, Z. phyaik. Chem., 126,431 (1921)
R E O ~ I Y E DJune 22.
1937.
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