OCTOBEH, 1936
INDUSTRIAI, AhD ENGINEERIYG CHEI1IISTRI-
tlie original resin about doiible that of the fractions. This difference in heat distortion and v-ater absorption vias due to the presence in the original resin of 10 to 13 per cent of very low polymer, ranging in molecular weight from 1000 to 4000, 15-hich n-as lost in the fractionation procedure. The presence of impurities such as cntalyst or monomer T v O U k ~also affect these properties, h i t these impurities are not likely to be present in ,sufficient quantity. The other physical properties listed show a pronounced variation JT-ith molecular weight. Tensile strength, impact strength. fatigue resistance, and the moduli of rupture and elasticity all show the same SfJrt of variation-that is, a rapid increase between molecular weights of 5000 and 8000 followed by a much more gradual increase above 8000. The average molecular weight of the highest fraction in Table I1 is 15,800, but fractions which show an average molecular \%*eight as high as 19,000 have been separated from other resins. Such frnctions show >very little change in physical properties
1155
froni fraction- A and B, except t'hat the plasticity is definitely higher. To summarize, these data show a rapid increase in mechanical strength with increasing niolecular weight u p to about' 8000, f o l l o ~ e dby a more gradual increase in the higher niolecular JTeight range. Similarly the heat distortion increases rapidly and the wat,er absorption decreases rapidly with increase in molecular weight up to about 4000; then they change more gradually.
Literature Cited (1) Rraerner and Van N a t t a , J.P h y s . Chem., 36, 3175 (1932). (2) Staudinger, "Hochmolekulare organische Verbindungen," p. 56, Berlin, J. Springer, 1932. (3) Ibid., p. 135.
(4) Ibid.,g . 179. ( 5 ) Willihnganr, McCluer, Fenske. and McGrew, IND. ESG. C H E h f . , Anal. Ed., 6, 231 (1934). RECEIVED September 2 , 1936.
Polymerization of Vinyl Acetate K . G . BLAIKIE AND R. N . CROZIER Shawinigan Chemicals Limited, Shawinigan Falls, Quebec, Canada
S
I S C E the discovery of vinyl acetate in 1912 (9, 16) numerous papers on its preparation (3, 8) and polymerization (3) have appeared. The present paper is an outcome of work carried out with a view to placing on a commercial basis the manufacture of polymerized vinyl acetate. It has been found that the factors affecting the polymerization and viscosity of the resulting polymer are impurities, temperature, solvents, catalyst, and percentage conversion. The polyvinyl acetate resins described are characterized by a number calculated from the outflow time, through 811 O d n a l d viscometer, of a standard solution in benzene:
T7 = = )SI = Ti = Db = TB = I'b
viscosity of polymer, centipoises absolute viscosity of benzene at 20" C. density of solution of polymer at 20" C. outflow time of solution at 20" C., seconds density of benzene at 20' C., seconds outflow time of benzene at 20" C., seconds
Impurities Polymerizations involving chain formation are extremely sensitive to promoters and inhibitors. Tiny1 acetate is no exception; thus it is necessary, especially for commercial production, t o pay particular attention to the purity of the ingredients as well as to the standardization of the conditions under which polymerization takes place. A good grade of commercial vinyl acetate contains over 99.9 per cent ester; the only impurities are traces of water, acetic acid, and acetaldehyde. The first two do not have much effect but acetaldehyde influences the viscosity t o a marked degree. The experimental method throughout has been to heat the material under reflux or in sealed glass tubes. Concordant results are obtained provided the time of reaction and the temperature are comparable. The effect of acetaldehyde is shown in the following table:
Vinyl acetate, parts Benzene, parts Catalyst, part Reflux period a t 73-78' C . , IIOUE 70conversion Acetaldehyde
60 40 0.0II 4.5 66-70 Viscosity
% 20
0.1 0.2 0.6
15
6
I n addition t(J these impurities, certaiii materials which actively inhibit the polynierization can be picked up by the ester and solvent unless precautions are taken. Chief among them are sulfur and copper compounds. Thus solvents must not, contain sulfur compounds, and tanks and pipe lines must not be assembled Fith gaskets containing sulfur. I n order to prevent polymerization in stills and columns, copper equipment is used : but as it is imperative that none of this material shall appear in the finished product, vapor lines and condensers should be constructed of aluminum or stainless steel. Cold Vinyl acetate, containing less than 0.03 per cent acetic acid, does not corrode iron, so that t>hismetal can be used for storage t,anks.
Temperature An increase in the temperature of polymerization has been shown to lower the viscosity of the product. The following table provides further evidence of this: Vinvl acetate, parts 90% butyl acetate, parts Catalyst, part Temp. Conversion
=
c.
70 75 80
70 30 0.07 Viscosity
% 68 70 65
23
19.5 16.5
Solvents The specific effect of variuu.' -01vents has been noted by several observers ( 1 1 , I J ) . Tables I and I1 a h o r clearly that not only the particular soh-ent, but also its concenhas a marked effect on the
INDUSTRIAL AiUD ENGINEEHISG CHEhIISTRY
11.56
One other factor appears to affect the viscosity of the final product-the presence of the polymer. -4s the reaction proceeds, the concentration of polymer increases, and the eviclence seems to support the view that it acts similarly to a solvent and depresses the viscosity. At least there is no doubt that a polymer, which has been freed from unchanged monomer by steam distillation, dried, and redissolved in fresh vinyl acetate, acts in the same way as benzene and does not rea(-t further with the monomer Under certain other conditions, which mill be described later, an increase in viscosity occurs which suggests that combination between chains takes place.
TABLE I. EFFECT OF SOLVENT Vinyl acetate, parts Solvent, parts Con-
Solvent
version
Catalyst, part Temperature,
50 50
Viscositr
29.0 68.5 22,6
C. 78
Con-
Solvent
veraoii
% Toluene Acetone Abs. alcohol
0 1
~
Viscnsity
% Acetic acid Ethyl acetate Benaene
2.9 3.0 5.6
78.7 89.3 55 0
6.8 8.2 18.2
T a n m 11. EFFECTOF SOLVESTCOXCESTRATIOP isulvent, 98% ethyl acetate: catalyst, 0.1%; temp., 73-77' C ' Ethyl Acetate Conversion Viscosity
%
Commercial-Scale Production
%
40 98 18.4 45 100 12.4 50 100 8.8 These runs were carried out under reflux. The rise in temperature froin 73-77O C. was the same in each run; thus they are exactly comparable.
Catalyst The catalyst used throughout is made by reacting sodium perborate with acetic anhydride in the appropriate solrent. The solution of acetyl peroxide is filtered from the insoluble residue and analyzed by measuring the iodine liberated from potassium iodide. The strength of the catalyst is expressed as sodium perborate. The viscosity of the polymer varies indirectly as the concentration of catalyst : Vinyl Acetate 50 Parts, 98% Ethyl Acetate, 50 P6rts; Tedp., 73-77' C. Catalyst Con\,ersion Viscosity Part % 0.1
100
0.025
100
8.8 11.8 13 8
...
0.05
Tiny1 Acetate, 70 Parts; 90% n$ 1 ice tate, 30 Parts; Temp., 80 . Catalyst Conversion TIisco8ity Part % 14.5 0.14 80 16.9 80 0.07 17.8 0.035 77
8.
Percentage Conversion The weight of polymer obtained per 100 parts of inononieric vinyl acetate used is called here the "percentage conversion." When vinyl acetate is polymerized in the absence of solvent, the viscosity of the resulting polymer rises with increase in percentage conversion. In one experiment the viscosity was 32 when the conversion was only 6 per cent. After 28 per cent of the vinyl acetate was converted to polymer, the viscosity had risen t o 71. The addition of solvent lowers the final viscosity and also tends t o suppress this rise in viscosity with increasing percentage conversion. If enough solvent is added, the viscosity becomes actually lower as the reaction proceeds. The more active a solvent is in lowering the final viscosity, the greater this effect will be. The following table illustrates this point (at 78" C.): -Benzene BenCataaene lyst % % 75 0.3
60 40
Solvent--ConVisrerslon cosity
88
7
% 43 79
3.4 3.1
0.1
54
0.03
73 81 ia
15.1 15.6 16.5 18.0 31.0 33.0 37.0
41 66
61
--
Tolu-
ene
'1 oluene as Soh ent -
Catalyst
Conversion
%
%
%
50
0.1
33 45 50
VOL. 28. KO. 10
-
Vis-
cosity 3.0 3.6 2.5
By applying the information given in the foregoing, it has been possible to obtain polyvinyl acetate of almost any viscosity up to about 60. Low-viscosity polymers can be made in toluene; higher ones are made in benzene. I n practice it is found convenient to keep the temperature and the duration of the reaction as constant as possible. Impurities in the reagents are reduced to a minimum by fractionation so that the variables which can be used for control are solvents and catalysts, or the catalyst and main solvent may be kept constant while the final adjustment is obtained by the addition of small amounts of acetaldehyde. A charge of vinyl acetate, benzene, and catalyst which 1 x 3 ~ been adjusted to give the desired viscosity is fed into a jacketed aluminum kettle fitted with an efficient stirrer. The bolution is gently refluxed for 5 hours while the temperature rises from 72" to 76" C. The thick solution is allowed to rtin into a tall narrow still through which free steam is passetl. The solvent, unchanged vinyl acetate, and steam are condensed; the top layer is separated, dried by distillation, and used in a subsequent run. During the last part of the steain didillation the pressure in the still is raised to about 50 pounds per square inch (3.5 kg. per sq. cm.). The increased temperature thus obtained assists in removing the last trace& of solvent and softens the gum so that it can be forced through the valve a t the bottom of the still Here it is picked up by an extruder which forms it into rods. These rods are cooled and sliced into thin shavings by a rapidly rotating cutter. The shavings are dried in a current of air a t a temperature not exceeding 60" C. The blocks of slightly sintered material, after cooling, are crushed in a swing hammer mill and stored in a revolving tank which acts as both a blending barrel and storage bin. Polyvinyl acetate has a high cold flow, and in warm weather it is impossible to prevent the material from caking. For this reason i t is advisable t o use comparatively m a l l containers for packing and to store them a t as low a temperature as convenient. The polymers obtained by this process are clear, colorlesa thermoplastic resins soluble in most organic solvents ( 8 , 1 5 ) .
Insoluble Polymerized Vinyl Acetate When vinyl acetate is gently refluxed with a small quantity of acetic anhydride and sodium perborate, a thick solution results. Samples removed from the reaction flask a t intervals show a gradually increasing viscosity until about 100 centipoises is reached, when the polymer begins t o become insoluble. On further heating, all the polymer precipitates as a whitish mass insoluble in the unchanged monomeric vinyl acetate; when heated still more, the acetate goes through the same cycle of changes. Eventually almost all the ester is converted into a polymer which is insoluble at temperatures below 100" C. in all the common organic solvents (1, 6). I n the presence of solvents the production of insoluble material is suppressed to a great extent. Mixtures of vinyl acetate, solvent, and catalyst, which consisted of sodium perborate with double its weight of acetic anhydride, were re-
DATAON SECOSDARY POLTNERIZ.%TION nun NO.
1131 1134 1138
T.ab. Boil-out ConTisversion cosity % 67 73 69 69 7
8.4 7.1 6.5 7.3
Large-Scale Steam Distn. ConVisversion cosity % 68 8.2 65 i3
Run No. 1141 1143 1145 1150 1152 1166 1168 1170
7.2 6.6
AV.
Lab. Boil-out ConVisversion oosity % 84 81 82 81 86 85 68 77 80.5
18.7 14.5 13.2 16.3 15.2 14.0 9.6 13.7 14.4
Large-Scale Steam Distn. ConVisversion cosity
Catalyat
% 0,6 0,6 0.6
0.6 0.6 1,2 1.2 1.2 0 2 0 6
Solvent
% Benzene, 20 Benzene, 30 Benzene, 30 Benzene, 40 Acetone, 10 Acetone, 10 Acetone, 20 Acetone, 30 Ethyl acetate 30 Ethyl acetate 30
4 16
16 15 12 15 15 15 15
75.5 74 53 48 39 14 7 88 67
Original 30 min. 1 hour Remarks Mostly insol. Some insol. .Much insol. Some insol. Trace insol. All sol. A11 sol. All sol. Much insol .Much insol
These data 3how clearly that for a moderate heating period, it is necessary to obtain a soluble polymer of relatively high viscosity before it will become insoluble. On a manufacturing bcale, however, when kettles are operated continuously, we find that small amounts of insoluble matter are formed along with polymers of loa- viscosity-viz., 2.5, 7, and 15,
Secondary Polymerization This term is used to describe a phenomenon which is observed during the steam distillation of polyvinyl acetate on a commercial scale. As explained a t the end of the paragraph on Percentage Conversion, it has not been possible to raise the viscosity of polymerized vinyl acetate once it has been isolated; but during the isolation of high-viscosity resins by steam distillation, it has been repeatedly found that the vibcosity of the final batch is considerably higher than that of a sample of polymerized vinyl acetate isolated immediately before running t o the steam still. The small sample can he rapidly boiled free from solvent and unchanged ester while a period of 6 to 8 hours elapses before the steam distillation is finished. During this operation the viscosity rises without any marked changes in the percentage conversion. The increase in viscosity without a corresponding increase in percentage conversion indicates definitely that cornbination between chains is occurring.
Depolymerization I n common with other similar colloids, polymerized vinyl acetate breaks down on milling. I n addition, depolymerization, as shown by a marked drop in viscosity, is brought about by acid hydrolysis, by heating in solvents such as acetic acid, and by alkaline hydrolysis. I n the case of the breakdown by mechanical means and by thermal depolwymerizationin acetic acid, there is no chemical change apart from rupture of the chains, provided the treatment is neither too severe nor prolonged.
Breakdown on Milling Polymerized vinyl acetate with a 1-iscosity of 60 was rolled on steam-heated compounding rolls to a temperature of 135 " C. for 6 hours. Samples were removed at intervals and their viwosities iletermined :
%
%
1057 1060 1097 1071
20.8 15.4 14.0 17.3 15.6 14.9 9.7 14.5 16 3
Time on Rolls
fluxed gently on a water bath a t about 75" C. The results are as follows: T'iscosi t y of Sol. Time of PolyHeating mer Hour? 4 B7
NO.
gr, ._
92 73 81 70 86 85 63 78 78 4
Large-Scale Steam Distn. CqnVisversion coeity
Lab. Boil-out ConVieversion oosity
Run
32.7 37.0 37.8 39.5 36.8
48 :34 35 63 45.0
Av.
Via-
56 35 39 65 48.8
Time on Rolls
cosity Centipoises 60.5 50.4 47.6
2 hours 4 hours 6 hours
45.1 50.1 46.0 59.0 50.1
Visoosity Centipoises 44.3 35.3 34.6
Depolymerization in Hot Acetic Acid Two per cent solutions of polymers of different viscosities were made u p and transferred to glass tubes. Samples (0.2gram) of insoluble polymer from kettles used to make soluble polymers of viscosity 45 and 2.5 were also placed in glass tubes, and 9.8 grams of acetic acid were added to each. The tubes were sealed and immersed in an oil bath a t 160" C. At definite intervals the bombs were removed and their relative viscosities determined as shown in Table IV. 'TABLE
Iv. RELATIVEVISCOSITT O F POLYMERS AFTER HE.4TING ACETICACID Relative Viscosity after Heating-a t 160' C.
IN
7 -
Viscosity No. of Polymer 4 30 300
Insol. 45 Insol. 2 . 5
No, Heating 2.0 5.4 20.7
...
. . ,
...
... 2.0 5.4 20.7
4
1 week 1.8 2.3 3.1 ?.4 1.5
2 weeks 1.8 2.8 3.7
4 weehs 1.8 3.4 3.7
... ...
... ...
A f t e r Heating at 100° C.-------
7 -
30 :100
34 hr. 1.8 2.4 3.4
2.0 5.2 16.3
1.9 4.8 11.6
1.9 4.4 10.1
~
1.9 4.0 7.0
The insoluble resin from polyvinyl acetate 45 did not dis3olve in acetic acid at 100" c. in 5 days but dissolved a t 125" C. in a few days. At the end of this time the resin was precipitated by pouring into water, and was then boiled with several changes of water to remove the acetic acid. The viscosity of this resin determined by the standard method was 38. Saponification showed i t t o be 99.6 per cent vinyl acetate. Polyvinyl acetate (viscosity, 300), after heating at 160" C., was isolated as already described. Its viscosity in benzene and its saponification value were determined as follows: Heating Period HOWS
Temp.
Viscosity
Vinyl Acetate
43 24
160 164
34 26
99.2 99.1
c.
%
After prolonged heating with acetic acid, evidence of decoinposition is shown. I n Table IV the viscosities of polyvinyl acetate 30 and 300 were starting to rise after they had been heated a t 160" C. for a week. A sample of insoluble polyvinyl acetate which was stable a t 125' C . for a week or so began t o decompose after 24 days at 160" C . Its saponification ralue indicated only 91.8 per cent as polyvinyl acetate, and the polyvinyl alcohol obtained from its hydrolysis was insoluble in water. This decomposition is in agreement with the disclosures of Staudinger and co-workers (22, IS). The above results were obtained in the presence of air. One or two experiments with tubes which had been evacuated showed a drop in viecmity. but the decrease was slover.
IXDUSTRIAL A N D EXGISEElUhG CHEMISTR1
1158
Hydrolysis with Concentrated Acid Samples of polyvinyl acetate of different riscoeities each weighing 2.58 grams were placed in 50-cc. volumetric flasks and covered with 10 cc. of concentrated hydrochloric acid. After standing a t room temperature overnight (16 hours), the thick solutions were diluted with water, immersed in a thermostat a t 20" C., and made up to 50 cc. with water. The time of outflow through an Ostwald viscometer was measured a t weekly intervals. The results are expressed as relative viscosities (ratio of outflow time of solution t o outflow time of solvent), Viscositya of Polyvinyl Acetate 2 7 15 30 40 50
--Relative 0 1.75 3.7 5.3 7.1 8.7 8.7 5.9
Viscosity at Weekly Intervale-4 ueeks 8 weeks 12 weeks
1 week 1.73 3.5 4.6
6.2
6.8 6.9
1.70 3.1 4.0 4.8 5.5 5.5 4.9
1 63 2.8 3.3 3.8 4 5 4.3 3.2
1.62 2.6 3.1 3.1 3.4 3.4 2.9
1mol.b 5.4 0 Measured by the standard method in benzene. 6 Insoluble polyvinyl acetate from kettle used t o inanufacture ri.;yinerired vinyl aoetate 45.
The concentrated acid lowers the \.iscushy niuch iaster than the dilute, but the alcohol eventually 1,econies inzuluLle in water and dilute acid. Polpiny1 acetate 1.5 was silowed to : t a d with 10 cc. uf concentrated hydrochloric acid for different periods of time and then diluted with water, snd the outflow p e r i d s ai the d i t ion were measured: Time Houra 16 18 72 120
which is rigorously stirred. The alcohol separates in granules or flakes. As ordinarily prepared by this method, the polyvinyl alcohol still contains 4 to 5 per cent saponifiable matter but is satisfactory for most purposes. The insoluble polymer can be hydrolyzed in the same way. The particles which swell without dissolving in the methanol begin to disintegrate about an hour after the addition of 0.4 per cent potash. In about an hour and a half the insoluble polymer has dissolved to give a thick homogeneous solution. A few minutes later, separation begins and the whole mass rapidly sets to an opaque gel which is worked up as described for the soluble form. Partially hydrolyzed resins are obtained by interrupting the alcoholysis a t intervals and precipitating with water. After exhaustively boiling with water, the resins are dried a t 130" C. under a vacuum of 24 inches (61 cm.). The polymerized alcohols prepared in this way can be readily reacetylated by means of pyridine and acetic anhydride a t 100" C. Polyvinyl acetate 15 and some insoluble resins were hydrolyzed, and the resulting polyalcohols were acetylated with pyridine and anhydride with the following results:
Insol.
Acid Hydrolysis with Dilute Alcoholic Acid Polyvinyl acetate is easily hydrolyzed by dilute alcoholic hydrochloric acid or sulfuric acid. The polyvinyl alcohol separates as a granular p m d e r , insoluble in organic qolvents but soluble in water (4). The alcohol prepared in this way cannot be completely reacetylated (12). This finding as confirmed in these experiments. After treating for 8 hours with an excess of pyridine and acetic anhydride, the resulting resin contained only 93.7 per cent polyvinyl acetate; heating for 24 hours gave a resin with 94.8 per cent. The difficulty in completely reacetylating polyvinyl alcohol prepared in this way points to the loss of some hydroxyl groups by the removal of water ( 5 ) . Whether this dehydration occurs during the hydrolysis or on drying the alcohol has not yet been ascertained, but there are indications that the change is accelerated by the presence of traces of acid which are very difficult to remove from the polyvinyl alcohol.
Alkaline Hydrolysis Polyvinyl acetate is readily hydrolyzed by ineans of alcoholic alkali. The normal method is to add an excess of alkali or alkali alcoholate to an alcoholic solution of the polyester. The precipitated polyvinyl alcohol is dissolved in water and dialyzed to remove sodium salts, and the polyvinyl alcohol is precipitated by the addition of alcohol (12). A much simpler method has been worked out by Price in these laboratories (10). Polyvinyl acetate is dissolved in dry methanol and treated with a small quantity (0.2 to 0.4 per cent) of caustic potash in dry methanol. Alcoholysis occurs and, after standing a t room temperature for some time, the polynierized alcohol separates as an opaque gel. Water inhibits the reaction. The product is isolated by dissolving the gel in boiling water, cooling, and pouring the solution into an excev of acetone
Time at
Polyvinyl Acetate No.
Polyvinyl
100' C. Acetate
Hours 8
15
16 24
Time at
Polyvinyl Acetate No.
Yo 100.1 99.6 99.9
Polyvinyl
100a C. Acetate
Insol. 45 Insol. 2.5
Hours
vo
8
99.1 99.8
8
Viscosity of Reacetylated Resins
Relative Visoosits 5.3 4.5 2.9
\ O L . 28, A.0. 10
Polyvinyl acetate 18.9 containing 99.5 per cent saponifiable matter as vinyl acetate was used for the following experiment e : Seven grams were heated for 8 hours at 100" C. with 14 cc. acetic anhydride and 21 cc. pyridine. The resin was recovered by precipitation with water. Aft,er thoroughly boiling with fresh changes of water, the resin was dried, first at 125" C. and then at 140" in the vacuum obtained by a mercury pump. The recovery was practically quantitative (viscosity, 18.2; per cent saponifiable matter, 99.6). A 33 per cent solution in dry methanol was prepared and divided into five portions, to each of which was added alcoholic potassium hydroxide, equivalent to 0.4 gram potassium hydroxide per 100 grams polyvinyl acetate. Alcoholysis was interrupted in the first four flasks at intervals of about 10 minutes. The fifth flask was left overnight. The partially hydrolyzed resins thus formed were worked up as previously described. They are all insoluble in benzene but dissolve in 80 per cent aqueous alcohol. The resins were reacetylated and the viscosities in benzene determined. The reacetylated product from the sample of polyvinyl alcohol Tvas again hydrolyzed and reacetylated: Polyvinyl Acetate,
%
Polyvinyl Acetate from 1st +etylation, yo
99.5 94.3 89.7 77.8 02.7 4.8
99:7 99.7 99.7 99.6 99.5
Insol. resin (99.4%) 45 Insol. resin 2 . 5
99.1 99.8
Ahs. Viscosity in Benzene 1s.: 16. 15.9 13.4 12.9 11.0
Polyvinyl Acetate from 2nd hcetylation, yo
.. .. ..
.ibs.
Viscosity in Benzene
..
..
98:s
ii:d
20.8 3.4
Co-polymer with Divinyl Ether Divinyl ether supplied by Merck Bt Company was redistilled in a vacuuni apparatus to remove stabilizers. A 1.8gram portion was mixed with 14.1 grams of vinyl acetate in a glass tube which was sealed ( A ) . A second tube containing vinyl acetate was also sealed ( B ) and both tubes were heated a t 79" C. for 6 hours. The contents of the tubes had set to stiff colorless gels. The tubes were opened and some acetone was added to dis-
OCTOBER, 1936
1NDUSTRIAL AND EKGINEERING CHEMISTRY
kolve the polymers. The coiitenta of tube -4were insoluble in acetone; the polymer in B was soluble and proved to be a typical, high-viscosity polyrinyl acetate. The material in A was scraped out. hoiled repeatedly Rith water. and dried a t 130" C. At this teinperaturc there was little or no evidence of fusion. This niaterial is unlike polyvinyl acetate, either soluGle or insoluble. It is unaffected by heating in acetic acid at 160" and even a t 180' C. I t swells in concentrated hydrochloric acid but does not dissolve. Saponification with standard alkali in alcohol was attempted. 1 value of 93.4 per cent was obtained but this figure is open to doubt as the saponified material was insoluble in aqueous alcohol and in water. This co-polymer is analogous to the products obtained by Staudinger and Heuer in bhe case of styrene and divinyl benzene ( I S ) .
Discussion of Results
-CH?-CHOAC-
1159
polymerized vinyl acetate by admixture with resins of the 11onhardening phenol-aldehyde type ( 7 ) . Thus, the suggestion is made that the polymers of vinyl acetate consist fundamentally of chains of various lengths which are joined by weak links to a greater or less degree as they are insoluble or soluble. Various stages in the polymerization are depicted graphically in formulas 1 and 2. I n formula 2 the number of cross links in different soluble polyniers will vary and be less than in the insoluble varietv: Soluble polymer of lox,- viscosity:
-CH~-CHO.~C-(CH?-CHO.~~) ,b--CH?-CHOA~2. soluble polSmer of higher riscosities and insoluble polymers:
(CH~-CHO.~C),,-CH~-CHO.~C-CH~-CHOACI
----cH?cHo.~~-(cH~--cHoA~)-
The rise in viscosity in the steam
the polyvinyl molecules. Preliminary -CH~-CHOAC-CH?-CHOACexperiments indicate that the rise becomes noticeable when the greater part of the volatile conWhen cross links of primary valences are introduced into stituents h a r e been removed, but this has not been definitely polyvinyl acetate, a body is obtained with the properties of established. Granting that this rise in viscosity does mean a the co-polymer of vinyl acetate with divinyl ether. It is union of molecules, it is reasonable to suppose that this union shown graphically in formula 3: occurs to a certain extent during tlie preparation of soluble polymer. The amount of interchain linking increases as the 3. Insoluble vinyl acetate-divinyl ether p o l w e r : viscosity of the polymer rises. Bt'audinger and others postulate a long -CH2-CHOAc-CH2-CH-(CH,-CHOAc),-CHOAc)n-CH2-CHOActhreadlike macromolecule coiisisting of a chain of monomeric molecules. If this chain-tochain union occurs a t the e d s of the mole-CH?-CHO.~~-C~~-~H-(C~?-~~O*~~~~-CH?-~H-~~*--CHOA~cules, the final result will be a "Staudinger chain" of greatly increased length. The behavior of the polymers of vinyl acetate of dif-CH:H-CHS-CHOAcferent viscosity, on milling, in hot acetic acid and in concentrated hydrochloric acid might be expected on account of the inherent instability of very long molecules, since This material is stable and does not break down to a soluble the treatment is severe. However, such a view can offer no exform. It is analogous to the inaolllble material obtained by planation of the behavior on alcoholysis where a polymer is deSt)audiilgerand Heuer (13). polymerized to a stable forin. Further treatment does not alter the viscosity of the product. S o r can it account for the Acknowledgment fact that the methods of degradation employed convert the inThe miters wish bo thank the directors and managemeiit of soluble polyniers to soluble bodies .ivhich in Some cases hare Shawinigan Chemicals Ltd. for permission to publish these rel.jscosities lower than the final obtained . & , hordinary sults. They are also grateful to H. K. Matheson, director of soluble polymers. research, and D. McIntosh, chief chemist, for their helpful inIt TTouldnot accoulltfor tile formation of the insoluble terest. terial which is obtained in a inanner strictly comparable to the v a y in which the soluble modification is made. I n fact,, Literature Cited there is evidence t'hat the soluble body is converted to the insoluble, in the instance described, simply by further reaction. (1, nlaikie, u.s. patent .ipplioation 447,428 (fled A ~ p r i25, l 1930; now in interference). Staudinger and Schwalbach (14) describe an insoluble poly( 2 , Elliot, Can. Chenz. J l e t . , 18, No. 8 (1934). mer obtained from vinyl acetate at about 200" C. They at( X I Ellis, Carleton, "Chemistry of Synthetic Resins," LIP. 1016-68, tribute its insolubility to a lattice or bridged structure resultYew l-ark, Reinhold Pub. Carp., 1935. ing from the fission of acetic anhydride between neighboring (4, H~~~~~~and Haehnel, B,,?,, 60, 1668 (1927). chain molecules. The material described here cannot be ( 5 ) Hermann and Haehnel, German Patent 480.866 (1929). 16) Hopff. Garbssh, and Teller, British Patent 328,848 (1932). formed in this way, since there is no evidence of deconipo(7) Irany, E. P., unpublished work. sition a t tlie temperatures of polymerization. This view is ( 8 ) Morrison and Shaw, Tra7ie. Electrochem. SOC, 43, 197 (1933). supported by saponification v a l u e s a - h i c h (9) hlylo, Ber., 45, 646 (1912). correspond to that of ordinary polyvinyl (10) Price, A. F., unpublished work. (11) Starkweather and Taylor, J. Am. Chenz. Soc., 52, 4708 (1930). acetate. (12) Staudinger, Frey, and Starck, Be,., 60, 1782 (1927). Severtheless, this type of structure seems (13) Staudinger and Heuer, Ibid., 67, 1164 (1934). to be suitable. Irany of these laboratories (14) Staudinger and Schwalbach, Ann., 488, 8 (1931). suggested that weak cross linkages existed in (15) Whitby, McNally, and Gallay, Brit. Chem. Abstracto, A1928, 1186. the insoluble polymer and that the ability of (16) Wohl and Mylo, Ber , 45, 329 (1912). the chains to form a lattice is in accord with his observations on the form stabilization of RECEIIEDSeptember 12, 1935.
b
A A
