POLYMERIZATION AND POLYCONDENSATION PROCESSES

15 Process for Preparing High-Molecular-Weight Polyformals of Alicyclic Diols W. J . JACKSON, Jr., and J . R. CALDWELL

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Research Laboratories, Tennessee Eastman Co., Division of Eastman Kodak Co., Kingsport, Tenn.

Low-melting polyformals were made by Carothers by heating aliphatic diols and dibutyl formal in the presence of acidic catalysts.

When attempts

were made to prepare polyformals of alicyclic diols by this method, low-molecular-weight, colored polymers were obtained.

A new process

was

therefore developed for preparing these polyformals.

In this process, a diol and paraformalde-

hyde are heated in a hydrocarbon solvent in the presence of an acidic catalyst, and water is azeotropically

removed.

Depending

upon the

type of diol, the polymer is built up to a high molecular weight in this solution or in the solid phase. This process is superior to the conventional dibutyl formal method in that polymers with high molecular weights and substantially no color can be obtained.

The process, developed for prepar-

ing polyformals of alicyclic diols, should also be applicable to various other types of diols.

polyformals were first prepared b y Carothers (S, 6) b y heating aliphatic diols and dibutyl formal i n the presence of acidic catalysts: HO-R-OH + C H 0-CH -OC H 4

9

2

4

9

-» ( - 0 - R - 0 - C H - ) 2

w

+ C H OH 4

9

After the butyl alcohol was removed, the polymers were built u p b y heating the melt under reduced pressure. Since these polyformals of aliphatic diols h a d very low melting points (below 75° C ) , their utility was limited. Apparently, no higher melting points have been reported for polyformals. I n attempts to obtain higher-melting polyformals, the following alicyclic diols were used: cis-, trans-, and 1 to 1 cis-/trans- mixture of 2,2,4,4-tetramethyl-l,3-cyclobutanediol ( I ) ; trans1,4-cyclohexanediol ( I I ) ; trans-1,4-cyclohexanedimethanol ( I I I ) ; a n d 2,5- or 2,6norbornanediol ( I V ) . Polyformals of h i g h molecular weight were not obtained from these diols b y interchange w i t h dibutyl formal. Carothers reported that a polyformal c a n be

200 In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

JACKSON AND CALDWELL

Polyformals of Alicyclic Diols

201

made with 1,4-eyclohexanediol by this method, but did not describe the polymer (3). Since no other method for preparing polyformals was described in the literature, a new process was developed. A diol, paraformaldehyde, and an acidic

V

H

(CH )«C

3

X

H

v

)C(CH )2

/

3

H ,0H

/ 0 H

OH


I H

W

CH 0H

H

2

HO HOCH

H

2

III

OH IV

catalyst are heated in a water-immiscible solvent, and water is removed as an azeotrope with the solvent (2). Some of the polymers prepared by this process could be built up in solution. Others attained high molecular weights when the particles were heated under reduced pressure at temperatures below their melting points. The reaction may be represented as follows: H O - R - O H + CH*0 -> ( - O - R - O - C H a - ) » + HaO This polymerization method was also applied to 1,10-decanediol, one of the aliphatic diols used by Carothers.

Experimental Materials. 2,2,4,4-TETRAMETHYL-1,3-CYCLOBUTANEDIOL. The diol was a commercial product (Tennessee Eastman Co.). Unless otherwise indicated, the diol consisted of a cis-/trans- mixture with about a 1 to 1 isomer ratio. The cisisomer was obtained from the isomer mixture by transforming the trans- isomer into an unsaturated aldehyde with aqueous sulfuric acid (4). The frarw-diol was obtained by preparing the diformate of the isomer mixture, separating the transderivative from the cis- derivative by recrystallization, and converting the transdiformate to the diol by methanolysis (5). ttotiS'l ,4-CYCLOHEXANEDIMETHANOL. The diol was obtained from the cis-/ trans- mixture by crystallization. The isomer mixture was a commercial product (Tennessee Eastman Co.). trans-1 ,4-CYCLOHEXANEDIOL. The diol was obtained by isomerization of a cis-/trans- mixture of the diol with an equimolar amount of sodium in refluxing diethylene glycol diethyl ether by a modification of the procedure of Batzer and Fritz ( I ) . 2,5- or 2,6-NORBORNANEDIOL. The compound was prepared by adding acetic acid across the double bond of the cyclopentadiene-vinyl acetate Diels-Alder adduct and then converting this diacetate to the diol, which was an isomeric mixture. 1,10-DECANEDIOL. The diol (Eastman-grade) was purified by recrystallization. PARAFORMALDEHYDE. The aldehyde (Baker and Adamson reagent grade, Allied Chemical Corp.) was, according to the manufacturer, of at least 95% purity. A sample was checked and found to be 96% pure, calculated as formaldehyde. SOLVENTS. The solvents were commercial grades, except benzene (Baker and Adamson reagent grade). The other solvents were distilled before use. CATALYSTS. The catalysts were commercial products. In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

202

ADVANCES IN CHEMISTRY SERIES

D I B U T Y L F O R M A L . T h e compound was prepared b y refluxing a mixture con taining 5.0 moles of formaldehyde, 11 moles of butyl alcohol, 25 grams of p toluenesulfonic a c i d , and 500 m l . of benzene. T h e water w h i c h was formed d u r i n g the reaction was collected i n a Dean-Stark trap attached to a Vigreux column. This required about 4 hours. T h e solution was then cooled, washed w i t h sodium bicarbonate solution, dried w i t h sodium sulfate, and distilled. T h e product, a colorless l i q u i d , boiled at 5 5 ° C , 6 m m . of H g , η ° 1.4061. T h e y i e l d was about 80%. D i b u t y l F o r m a l M e t h o d . A procedure similar to that of Carothers (8,6) was used i n preparing polyformals from diols and dibutyl formal. Usually, 0.10 mole of d i b u t y l formal, 0.105 mole of the cyclic diol, and a catalytic amount of an acidic compound were heated i n a metal bath at the boiling point of dibutyl formal ( 1 8 0 ° C ) . If no b u t y l alcohol distilled over i n about 0.5 hour, more catalyst was added. W h e n insufficient b u t y l alcohol was obtained after about 2 hours, more catalyst was added. W h e n an appreciable amount of the alcohol had been collected, the bath temperature was increased to 200° C . for about 1 hour. T h e pressure was then reduced to 0.5 m m . of H g , while the prepolymer was stirred. If buildup of polymer d i d not take place i n 1 to 2 hours (indicated b y an increase i n viscosity of the m e l t ) , the bath temperature was increased to 250° C . T h e polyformals w h i c h were obtained i n this manner from the alicyclic diols were highly colored, a n d their inherent viscosities were below 0.4 (determined using 6 0 / 4 0 phenol-tetrachloroethane mixture as solvent). Catalysts w h i c h were used were ferric chloride, methanedisulfonic acid, camphorsulfonic acid, anti mony trifluoride, and titanium tetrafluoride. Polymers were not obtained w i t h the latter two. Paraformaldehyde M e t h o d . 2,2,4,4-TETRAMETHYL-1,3-CYCLOBUTANEDIOL. A 2-liter, three-necked flask was fitted w i t h a glass stirrer, thermometer, and D e a n Stark trap w h i c h was filled w i t h distilled cyclohexane a n d attached to a watercooled condenser. In the flask were placed 216 grams (1.5 moles) of 2,2,4,4tetramethyl-l,3-cyclobutanediol ( l to l cis-/trans- mixture), 52.2 grams (1.65 moles, if 9 5 % pure) of paraformaldehyde, 1200 m l . of distilled cyclohexane, a n d 0.20 gram of methanedisulfonic acid i n a 10 to 2 5 % aqueous solution. ( T h e catalyst solution had been treated w i t h Darco G - 6 0 to remove all color.) W h i l e this mixture was stirred at 60° C , the paraformaldehyde depolymerized to form aldehyde, w h i c h reacted w i t h the diol. Complete reaction of these t w o com ponents was indicated when they h a d gone into solution. This required about 1 hour. T h e temperature of the mixture was then raised to 7 0 ° C . W h i l e this tem perature was maintained w i t h an automatic controller, the pressure was reduced until the cyclohexane was refluxing rapidly. This was accomplished b y con necting the top of the reflux condenser through a d r y ice trap to a vacuum line. T h e pressure was adjusted w i t h a valve w h i c h bled air into the system between the condenser and trap. T h e reflux was fairly r a p i d i n order to remove the water at a reasonable rate. N o r m a l l y , about 5 hours was required to remove a l l of the water. I n addition to the water w h i c h was i n the catalyst solution, about 31 m l . of water collected i n the Dean-Stark trap. (Apparently the aqueous layer con tained some products from the excess formaldehyde, because the theoretical amount was 27 ml. ) D u r i n g the later stages of the reaction, some black material collected on the wall of the flask. One-half hour after no more water was obtained i n the Dean-Stark trap, the hot solution was decanted from the black residue and filtered through a fluted filter. T h e solution was kept hot d u r i n g the filtration step to prevent the separation of prepolymer. T h e cyclohexane was then distilled, while the solution was heated under reduced pressure (water aspirator) o n the steam bath. T h e residue con sisted of white particles and powder with an inherent viscosity of 0.1 to 0.2. ( A l l inherent viscosities were determined using 60 to 40 phenol-tetrachloroethane mix ture as solvent. ) T h e yield was virtually quantitative. Analysis. Calculated for C H 0 : C , 6 9 . 3 % ; H , 10.3%. F o u n d : C , 6 8 . 7 % ; H , 10.3%. After the above prepolymer was ground to pass a 20-mesh screen, it was heated under a pressure of 0.1 m m . of H g for 1 hour, while the temperature was 2


D

9

1 6

2

In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.



raised from 160° to 260° C . T h e temperature was then held at 260° C . for 1 hour. T h e polymer was obtained as white particles w i t h inherent viscosities of 1.2 to 1.3. Analysis. Calculated for C « H 0 : C , 6 9 . 3 % ; H , 10.3%. F o u n d : C , 6 9 . 2 % ; H , 10.2%. Polyformals of the individual cis- and trans- isomers of the diol were similarly prepared. T h e thermal stability of the polyformal of the cis-/trans-diol mixture was increased b y treatment w i t h an amine. A mixture of 2 grams of polyformal, 0.02 gram of tributylamine, a n d 10 m l . of methanol was stirred for 0.5 hour. W h e n the polymer was heated i n a film press at 300° C . for 4 minutes, the inherent viscosity decreased from 1.21 to 0.99. T h e inherent viscosity decreased to 0.81 when the polymer had not been stabilized. T h e polymer could also be stabilized b y treatment w i t h acetic anhydride a n d sodium acetate. A mixture of 20 grams of the polyformal (20- to 40-mesh particles), 100 m l . of acetic anhydride, and 0.2 gram of sodium acetate was stirred for 3 hours at 130° C . T h e polymer was then collected a n d washed by stirring it w i t h acetone, methanol, a n d water several times. W h e n the polymer was heated i n a film press at 300° C . for 4 minutes, the inherent viscosity de creased from 0.96 to 0.85. T h e melting ranges a n d solubilities of the tetramethylcyclobutanediol poly formals are given i n Table I. £ r a n s - l , 4 - C Y C L O H E X A N E D i O L . A mixture of 11.6 grams (0.10 mole) of transI , 4-cyclohexanediol, 3.3 grams (0.105 mole, if 9 5 % pure) of paraformaldehyde, 0.05 gram of p-toluenesuTfonic acid, a n d 40 m l . of benzene was stirred at 6 0 ° C . for 1 hour. T h e solution was then refluxed for 2 hours, and the water w h i c h formed was collected i n a Dean-Stark trap filled w i t h benzene. M o r e paraformaldehyde (0.15 gram) was added, and the mixture was stirred at 60° C . for 0.5 hour before refluxing for 1 hour. Another 0.15 gram of paraformaldehyde was added, and the simmering a n d refluxing procedures were repeated. (These extra additions of paraformaldehyde were probably not necessary i n this procedure, since solidphase b u i l d u p was used, a n d only t w o experiments were carried out w i t h this diol. ) T h e benzene was then removed under reduced pressure, while the mixture was heated on the steam bath. After the white, crystalline residue was ground to pass a 40-mesh screen, it was heated under a pressure of 0.1 m m . of H g for 1.5 hours, while the tempera ture was raised from 150° to 193° C . T h e temperature was then held at 193° C . for 2 hours. T h e polymer, a white powder, h a d an inherent viscosity of 0.53. Its melting point and solubilities are given i n Table I. T h e elemental analysis was not obtained. trans-1,4-CYCLOHEXANEDIMETHANOL. A mixture of 28.8 grams (0.20 mole) of £rans-l,4-cyclohexanedimethanol, 6.3 grams (0.20 mole, i f 9 5 % pure) of para formaldehyde, 0.10 gram of p-toluenesulfonic acid, and 40 m l . or benzene was stirred at 60° C . for 1 hour. D u r i n g this time the diol and paraformaldehyde went into solution. W h i l e this mixture was refluxed for 1.5 hours, 3.5 m l . of water collected i n a Dean-Stark trap w h i c h was filled w i t h benzene a n d attached to the flask. Additional paraformaldehyde (0.3 gram) was added, and the mixture was stirred at 60° C . for 0.5 hour a n d then refluxed for 1 hour. Since the mixture was very viscous, more benzene was added. Paraformaldehyde (0.3 gram) was added twice more, and the heating and refluxing procedures were repeated. It was also necessary to a d d more benzene because the solution again became very vis cous. T h e catalyst i n the polymer solution was neutralized b y adding a few drops of ammonium hydroxide ( a n d some ethanol to a i d m i s c i b i l i t y ) . T h e solvent was removed from a portion of the solution b y heating on the steam bath under reduced pressure. T h e polymer had an inherent viscosity of 0.57. Analysis. Calculated for C H 0 : C , 6 9 . 3 % ; H , 1 0 . 3 % . Found: C, 6 8 . 6 % ; H , 10.4%. T h e remainder of the benzene solution was poured into methanol w i t h stirring. T h e white powder obtained h a d a n inherent viscosity of 0.67. Its melting point and solubilities are given i n Table I. Analysis. Calculated for C H 0 : C , 6 9 . 3 % ; H , 1 0 . 3 % . F o u n d : C , 6 8 . 6 % ; H , 10.4%. Perchloric acid was used as the catalyst i n a procedure similar to that w i t h p 1 6


203

9

9

1 6

2

1 6

2

2


204

ADVANCES IN CHEMISTRY SERIES Table I.

Physical Properties of polyformals of Alicyclic Diols


Diol 1 / l m-/*rûJW-2,2,4,4-tetramethyl-l ,3-cyclobutanediol «>-2,2,4,4-Tetramethyl-l,3-cyclobutanediol trans-2,2,4,4-Tetramethyl-l, 3-cyclobutanediol trans A ,4-Cyclohexanediol trans A ,4-Cyclohexanedimethanol 2,5- or 2,6-Norbornanediol

Melting Range, ° C.°,*> 283- 291

Solubility* ChloroHot form toluene Sol. Sol.

284-289 275-280 206-210 83-86 83-98

Swollen Insol. Insol. Sol. Sol.

Swollen Insol. Insol. Sol. Sol.

° The lowerfigureof each range was the temperature at which the polymer began to soften. The higherfigurewas the temperature at which the polymer began to flow. Melting ranges of tetramethylcyclobutanediol polyformals were determined under nitrogen in sealed capillaries. In air, these polymers melted at about 200° to 210° G. Melting ranges of the other polymers were determined in air with polarized light. They melted at approximately the same temperatures under nitrogen. All of the polyformals were soluble in hot tetrachloroethane and insoluble in methanol, ethyl acetate, and naphtha. 6

c

toluenesulfonic acid. T h e components of the reaction mixture were 43.2 grams (0.30 mole) of trans- 1,4-cyclohexanedimethanol, 11.3 grams (0.36 mole, if 9 5 % pure) of paraformaldehyde, 120 m l . of benzene, a n d 1 drop (0.05 gram) of 6 0 % perchloric acid. T w o 0.3-gram portions of paraformaldehyde were added w i t h a 1-hour stirring period at 60° C . a n d a 1-hour refluxing period after each addition. T h e catalyst was neutralized as before and the benzene was removed. T h e poly mer h a d an inherent viscosity of 0.88. 2,5- OR 2,6-NORBORNANEDIOL. This polymer was prepared b y a procedure similar to that for cyclohexanedimethanol using p-toluenesutfonic a c i d as catalyst. After concentration of a portion of the benzene solution, a polymer w i t h a n i n herent viscosity of 0.28 was obtained. W h e n the benzene solution was poured into methanol, a semisolid product was obtained. After being dried, the product, a clear, brittle resin, h a d an inherent viscosity of 0.49. Its melting range a n d solubilities are given i n T a b l e I. Analysis. Calculated for C H 0 : C , 6 8 . 6 % ; H , 8.6%. F o u n d : C , 6 8 . 5 % ; H , 8.6%. 1,10-DECANEDIOL. T h e polymer obtained from this diol was prepared simi larly to that from cyclohexanedimethanol, but twice as m u c h p-toluenesulfonic acid was used as catalyst a n d a 2 0 % excess of paraformaldehyde was present at the beginning of the reaction. After concentration of a portion of the benzene solution, a polymer was obtained w i t h an inherent viscosity of 0.87. W h e n the catalyst was not neutralized before concentration, the polymer was degraded and an inherent viscosity of only 0.27 was obtained. 8

1 2

2

Discussion Description of Process. T h i s process is superior to the conventional d i b u t y l formal method i n that polyformals can be obtained w i t h h i g h molecular weights and substantially no color. A mixture of a diol, paraformaldehyde, acidic catalyst, and hydrocarbon solvent is stirred at 6 0 ° C . for about 1 hour. D u r i n g this time, the paraformaldehyde depolymerizes and reacts w i t h the diol. W h e n complete solution is attained, the mixture is refluxed a n d the water formed i n the reaction is azeotropically removed. W h e n the prepolymer is to be built u p i n solution, two or three additional increments of paraformaldehyde are added a n d the reaction is continued. T h e viscosity of the solution increases as the molecular weight of the polymer increases. W h e n the prepolymer is to be built u p b y the solid-phase method, the solvent is removed and the prepolymer isolated. Prepolymers from the tetramethylcyclobutanediol isomers a n d from cyclohexanediol were built u p b y the solid-phase method—that is, the 2 0 - to 40-mesh




205


particles were heated under reduced pressure at temperatures somewhat below their melting points. T h e polyformals of cyclohexanedimethanol, norbornanediol, and decanediol melted too l o w to be built u p b y this method, but were effectively built u p i n solution. V e r y l o w molecular weights were obtained when the p r e polymers were built u p i n the melt phase under reduced pressure. T h e solid-phase method of b u i l d i n g u p polyformals is applicable only to high-melting polymers. T h e required melting point is not k n o w n , but the poly formal of rrafW-l,4-cyclohexanediol melted at 206°—10° C . a n d that of the c i s - / trans- mixture of 2,2,4,4-tetramethyl-l,3-cyclobutanediol melted appreciably higher. T h e solution method d i d not appear to be applicable to b u i l d i n g u p the poly formals of these two diols, since inherent viscosities below 0.4 were obtained. T h e solution method may be most applicable to primary diols, such as cyclohexanedi methanol a n d decanediol, w h i c h gave polyformals w i t h inherent viscosities of 0.9. Elemental analyses of the polyformals agreed w i t h or were reasonably close to the calculated values; therefore, the polymers contained substantially no poly(methylene oxide) i n the chains. Since excess formaldehyde was used i n pre paring the prepolymers, presumably their chains were terminated w i t h hydroxymethyl groups. Both water and formaldehyde must then be eliminated during the buildup of polymers: χ HOCHsi-O-R-O-CHs-J^OH -» ( - 0 - R - 0 - C H - ) ^ + x CH 0 + χ H 0 2

2

2

Reaction Variables. A n excess of paraformaldehyde was necessary ( 15 to 35 mole % excess was used) when the prepolymers were built up i n solution. A n excess evidently was not necessary when the prepolymers were built u p i n the solid phase. I n experiments w i t h tetramethylcyclobutanediol, a polymer w i t h an inherent viscosity of 1.2 was obtained when the diol was present i n 5 mole % excess, but the polymer was brown. W h e n the paraformaldehyde was i n excess, the amount was not critical, but it was necessary to use a m i n i m u m of about 10 mole % excess i n order to obtain white polymers. Polyformals w i t h inherent vis cosities of 0.5 or greater were obtained when the molar excess of paraformaldehyde ranged from 2 to 4 0 % . T h e highest inherent viscosities (above 1.0) were ob tained when the excess was about 10 mole % . W h e n trioxane was used as the formaldehyde source instead of paraformaldehyde, reaction d i d not take place (no water was obtained). Benzene was a satisfactory solvent for preparing the polyformals of a l l the diols, except tetramethylcyclobutanediol. T h e polyformal of this d i o l could be readily obtained when benzene was used, but, unlike the polyformals of the other diols, this one was somewhat brown. T h e color was due to a benzene-soluble impurity w h i c h was formed during the reaction. W h e n the prepolymer was built up, this color was greatly intensified and speckled polymer particles were obtained. A more satisfactory solvent was one i n w h i c h the dark impurities were insoluble. T h e y could then be removed b y filtration before concentration of the prepolymer solution. Hexane gave good results, but the purity of the hexane appeared to be critical. ( B r o w n - a n d tan-speckled polymer particles were often obtained after the solid-phase b u i l d u p , unless the hexane h a d been treated with oleum. ) C y c l o hexane gave white polymers w i t h h i g h inherent viscosities after b u i l d u p i f the maximum reaction temperature during prepolymer formation was limited to 7 0 ° C . This was accomplished b y carrying out the reaction under slightly reduced pres sure. (Colored polymers were obtained if the prepolymer preparation was carried out i n cyclohexane at its normal boiling point of 80° C.)



206

ADVANCES IN CHEMISTRY SERIES

Effective catalysts for preparing the polyformals were p-toluenesulfonic acid, camphorsulfonic acid, methanedisulfonic acid, and perchloric acid. Various other acidic compounds were evaluated as catalysts w i t h tetramethylcyclobutanediol. In these experiments, 0.5 to 1.0 gram of acidic compound per mole of tetramethyl cyclobutanediol was normally added. If insufficient water was obtained, more catalyst was added. If the prepolymer was obtained but an appreciable amount of brown color was present, less catalyst was then used. Compounds w h i c h d i d not catalyze the reaction (no water obtained) were phosphoric acid, zinc chloride, trifluoroacetic acid, and heptafluorobutyric acid. Incomplete reactions (insuffi cient water) took place w i t h concentrated hydrochloric acid, concentrated nitric acid, zinc fluoroborate, or Amberlite I R C - 5 0 ion exchange resin as catalyst. A prepolymer was obtained when boron trifluoride etherate was used, but buildup d i d not take place i n the solid phase (catalyst probably too volatile). Brown or speckled-brown polymers (after solid-phase buildup) were obtained with catalysts containing sulfonic acid groups (benzenesulfonic, dodecylbenzenesulfonic, sulfoacetic, methanetrisulfonic, sulfuric, p-toluenesulfonic, camphorsulfonic, and meth anedisulfonic acids). T o obtain white polymers from tetramethylcyclobutanediol it was necessary to treat the solvent and prepolymer reaction mixture as previously described. ( W h i t e polyformals were obtained from the other diols without this treatment. ) In these experiments w i t h tetramethylcyclobutanediol, it was found that meth anedisulfonic acid gave higher polyformals than the other catalysts. Inherent viscosities up to 1.7 were obtained, whereas values of only 0.8 to 0.9 resulted with camphorsulfonic acid or p-toluenesulfonic acid and 0.7 when perchloric acid was used. It was necessary to use 0.002 to 0.005 equivalent of camphorsulfonic acid or toluenesulfonic acid per mole of diol i n order to obtain the polyformal, but 0.001 equivalent of perchloric acid or 0.001 to 0.002 equivalent (0.0005 to 0.001 mole) of methanedisulfonic acid was sufficient to catalyze the polymeriza tion i n the various solvents. W h e n appreciably less catalyst was used, the poly mers d i d not b u i l d up, and when appreciably more was used, brown polymers were obtained. Titration indicated that almost all of the methanedisulfonic acid catalyst (or its reaction products) was present i n the black material w h i c h was deposited on the flask walls during the latter stages of the tetramethylcyclobutanediol prepolymer preparation when hexane was the solvent. Since the catalyst is very soluble i n water and insoluble i n hydrocarbons, it evidently came out of solution w i t h some decomposition products when no water remained i n the system. A n analysis of the prepolymer indicated that only 0.002% sulfur ( 1% of the original catalyst) was present. After solid-phase buildup, less than 0.001% sulfur was found i n the polymer. T h e r m a l Stabilization of Polyformals. Polyformals, built up i n solution, were neutralized w i t h a little ammonium hydroxide when they were to be isolated by concentration under reduced pressure on the steam bath. This prevented break down of the polymer because of the acidic catalyst. T h e degradation was par ticularly bad w i t h polyformals obtained from primary diols (cyclohexanedimeth anol and decanediol). In one experiment, the polyformal of decanediol was ob tained w i t h an inherent viscosity of 0.9 when the catalyst had been neutralized and 0.3 when it had not been neutralized. Breakdown under these conditions was not observed w i t h the prepolymer of tetramethylcyclobutanediol. Degradation of the polyformal of tetramethylcyclobutanediol occurred when the polymer powder was heated i n a film press at 300° C . T h e decrease i n i n In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.




207

herent viscosity was 3 3 % (1.2 to 0.81) when the polymer was heated for 4 minutes. W h e n the polymer was stabilized b y stirring the particles i n methanol with 1 weight % of tributylamine, the reduction i n inherent viscosity was 1 8 % under these conditions. Appreciably less stabilization was obtained w i t h ammonia, trimethylamine, or pyridine. Presumably, this stabilization is due to neutraliza tion of the acidic catalyst. Acetylation of the polymer end groups by heating with acetic anhydride a n d sodium acetate was also effective i n stabilizing the polymer. After this treatment, the decrease i n inherent viscosity was only 1 1 % under the above conditions. Physical Properties of Polyformals. T h e polyformals of the alicyclic diols had higher melting points than any previously reported for polyformals. Those of the tetramethylcyclobutanediol polymers were unusually h i g h , about 280° to 290° C . under nitrogen (Table I ) . Surprisingly, these polymers softened at about 200° to 210° C . i n air. Since this lower melting range was due to air oxidation of the polymers, it was possible to protect them by the addition of conventional anti oxidants. T h e other polyformals h a d substantially the same melting points under nitrogen as i n air. A l l of the polymers were soluble i n hot tetrachloroethane, but, unexpectedly, the polyformal of the tetramethylcyclobutanediol isomer mixture was also soluble in chloroform and i n hot toluene. Since formais are readily hydrolyzed by dilute acids, polyformals w o u l d be expected to be unstable to acids. T h e tetramethylcyclobutanediol polyformal, however, was unusually resistant to acid hydrolysis. A 1-mil film d i d not begin to disintegrate i n 1 0 % hydrochloric acid at 100° C . until after 4 hours. T h e re sistance of this polymer to alkaline hydrolysis was outstanding. A film d i d not begin to disintegrate when immersed i n 1 0 % sodium hydroxide solution at 100° C . for 7 days. Acknowledgment Thanks are due R . G i l k e y and K . P . Perry for their contributions to this work. Literature Cited (1) Batzer, H., Fritz, G., Makromol. Chem. 14, 211 ( 1954 ). (2) Caldwell, J . R., Jackson, W . J., Jr. ( to Eastman Kodak Co. ), U. S. Patent 2,968,646 ( Jan. 17, 1961 ). (3) Carothers, W . H. ( to Ε. I. du Pont de Nemours & Co. ), Ibid., 2,071,252 ( Feb. 16, 1937 ). (4) Hasek, R. H., Clark, R. D., Chaudet, J . H.,J.Org. Chem. 26, 3130 ( 1961 ). (5) Hasek, R. H., Elam, E . U., Martin, J. C., Nations, R. G., Ibid., 26, 700 ( 1961 ). (6) Hill, J . W., Carothers, W . H.,J.Am. Chem. Soc. 57, 925 ( 1935 ). RECEIVED September 6,1961.


POLYMERIZATION AND POLYCONDENSATION PROCESSES

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