Ionic Polvmerization of Some -
Vinyl Compounds C. E. SCHILDJLNECHT, A. 0. ZOSS, AND FREDERICK GROSSER General Aniline & Film Corporation, Euston, Pa.,and Grasselli, N . J .
*-
c
B
T
tively low polarity attached T h e cationic polymerization of vinyl-type monomers is to the second carbon atom. briefly reviewed. The polymerizations of lower alkyl vinyl ionic or polar-type polyPrice has suggested that those ethers in different types of systems are discussed, particumeriaations have received monomers undergoing ionic larly in relation to monomer structure and the properties comparatively little attention polymerization usually bear of the vinyl ether polymers formed. A number of experiin comparison to the free substituents promoting the ments are included bearing upon the kinetics of vinyl radical or thermal-induced release of electrons (20). alkyl ether polymerization, and upon the nature of isompolymerization of vinyl and Many of these monomers erism in polyvinyl isobutyl ethers and in polyvinyl related compounds. Of ionic show the possibility of resomethyl ethers. Some observations of cationic polymeripolymerizations a t low temnance with mobile electrons zation of vinyl methyl ketone, N-vinylpyrrolidone, and peratures with Friedel-Craf ts of the double bond, ether OXYN-vinylcarbazole are included. type catalysts, most familiar gen, nitrogen, and the benis the work on the preparation zene ring. Table I, column of isobutylene (2methylproA, shows examples of monomers which respond to Friedel-Crafts pene) high polymers (SS),isobutylene copolymers (3d), a-methylcatalysts a t low temperatures, but ordinarily do not yield high styrene polymers (I&’), and vinyl alkyl ether polymers (26, 27). homopolymers by free radical catalyzed or thermal polymerizaThis paper discusses the cationic polymerization of several lower tion. Most of these monomers respond to such ionic catalysts as alkyl vinyl ethers and includes some observations on the ionic polyboron fluoride and aluminum chloride (cationic polymerization) merization of vinyl methyl ketone, N-vinylcarbazole, and N-vinylbut do not respond well t o sodium (anionic polymerization). pyrrolidone. I n this paper only homopolymerizations giving Styrene and butadiene are well known examples of olefinic products of comparatively high molecular weight are considered. monomers which respond both to ionic polymerization and to Ionic polymerizations show a i d e diversification with respect to peroxide induced polymerization. Divinyl ether, vinyl methyl temperature, kinds of catalysts, diluents, phases involved, and ketone, AT-vinylpyrrolidone, and N-vinylcarbazole are found to kinetic characteristics. Many of these factors differ materially belong in this group, shown in column B of Table I. Most from the more familiar examples of free radical initiated addition monomers bearing strongly negative groups, as well as ethylene polymerization. It is of interest to compare vinyl alkyl ether itself, give high polymers by peroxide or thermal polymerization polymerization a t low temperatures with published work on the but not readily by Friedel-Crafts catalysts. These include vinyl ionic polymerization of isobutylene. halides, vinylidene halides, vinyl esters, acrylic esters, and methaThe paper includes some further investigation into the nature crylic esters listed in Table I, column C. of isomerism in polyvinyl isobutyl ethers and polyvinyl methyl ethers (25-27). The type of catalpt, the method of carrying out METHODS OF IONIC POLYMERIZATION OF VINYL ETHERS the polymerization, and special solvent activators have all been shown capable of influencing the degree of order and physical BULKPOLYMERIZATION. I n the scmplest cases the polymerizaproperties of the products. Except where otherwise stated, tion occurs in the liquid monomer phase and the polymer usually the‘se reactions were carried out in Pyrex vessels without excluremains dissolved. Ionic catalysts completely or partially solusion of air. ble in the monomer phase are ordinarily used for the bulk polyThe comparative polymerizability of a series of lower alkyl merization. Sirupy and balsamlike polymerizates were prepared vinyl ethers with boron fluoride and boron fluoride etherate cataby bulk reaction from lower alkyl vinyl ethers by Wislicenus (S), lysts has been correlated by assuming equilibria between boron Chalmers (4, Reppe and co-workers ($2, as), and Russian workfluoride associated with the double bond and with the vinyl ers (29). The following list of hydrolyzable inorganic halides ether oxygen atoms as influenced by steric factors. Some of of the Friedel-Crafts type are among those found to be effective these same considerations may apply also to vinyl ketones, N catalysts in earlier work and in this laboratory: boron fluoride, vinyl amides, and N-vinyl amines, where the vinyl group may boron chloride, aluminum chloride, aluminum bromide, stannic compete with oxygen and nitrogen as electron donors. chloride, ferric chloride, zinc chloride, silicon chloride, titanium
HE characteristics of
MONOMER RESPONSE TO DIFFERENT CATALYST TYPES
Vinyl-type monomers (“ethenoid” monomers) capable of forming homopolymers readily by addition polymerization arc, characterized by the terminal methylene group attached to a
\ /
second carbon atom by an olefinic double bond, C=CH2. Tetrafluoroethylene and chlorotrifluoroethylene, which respond to peroxide-catalyzed polymerization, are special cases where the small fluorine atoms can replace hydrogen of the methylene group. Those monomers responding best to ionic catalysts contain, in addition to the terminal methylene group, substituents of rela-
tetrachloride, gallium trichloride, and antimony pentachloride. Solid aluminum chloride is relatively inactive under conditions in which i t does not dissolve. A second class of ionic catalysts are the complexes with FriedelCrafts agents--e.g., boron fluoride-diethyl ether, boron fluoride dihydrate. These catalysts are definite compounds capable of purification which, a t a given temperature range, ordinarily give more mild polymerization reactions than the free metal halide. A third class of ionic catalysts comprises anhydrous inorganic acids, such as sulfuric acid and hydrofluoric acid, but these are ordinarily not suitable for preparing high polymers from the lower alkyl vinyl ethers. Certain silicates including bleaching earths, after activation by heating, can act as mild catalysts at relatively
2891
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
2892
1. RESPONSE OF OLEFINIC TYPES
TAR1.E
A High Polymers by Ionic Polymerizstion Only isobutylene ( 3 3 )
kfOVOMERS
B High Polymers b y Both Ionic a n d Peroxide Polyineriaation
/CHa
TO
CATALYST
c High Polvmers by Perdxide or Thermal Polymerization Ethylene HzC=CHv
H.C: -s=C
\
CHa Butadiene HsC-CH---C>H=CHs Divinyl ether H2C =C H
b
Vinylidene halides OHg=CX%
/
A2C-CFI
Methyl vinyl ketone 0
// ILC=CH- -C-CHa
Vinyl esterH?C==CH
\ / R/ ! = O
n-laopropenyltolue
Vinyl alkyl ethers ($3, 86,871 RsC':-CH '0
/ R
hlethactylic ester. CHs
H,C=C
/ \
C= 0 bR
M e t h i 1 ester of vinyl oxyacetie acid (6)
R*CeCH b-CHKOOCHs
high teniperatures, particularly in bulk polymerization. Lower alkyl vinyl ethers also respond to catalysis by iodine and by 4 f u r dioxide but do not polymerize under the action of sodium. Bulk polymerization in the temperature range 0' to 100" Cy. has been used commercially for preparing sirupy, balsamlike, or semisolid polymers from lower alkyl vinyl ethers. Examples include polyviny1 methyl ether manufactured in this country and in Germany and Igevin J (viscous liquid polyvinyl isobutyl ether). Once started, the rate of heat evolution in bulk ionic polymerizations is often of a higher order than t h a t ordinarily encountered in peroxide catalysis and therefore must be carefully controlled to prevent reactions of considerable violence. Polymers of viscositv ?sp/c = 0.2 to 0.8 are typical of the products obtained irom vinyl methyl or vinyl butyl ether monomers by bulk polymerization in the temperature range 0 " to 100' C . (viscosities determined a t 25' C, using solutions of 0.1 to 1.0 gram per 100 ml. of benzene). SOLUTIOXPOLYMERIZATION. Ordinarily, greater dilution of vinyl monomers in peroxide-catalyzed polymerization gives products of lower degree of polymerization when other factors remain constant. However, 1 to 4 parts of suitable solvents can have the practical result of giving higher polymers in many ionic polymerizations. This results in part from better control of temperature in the presence of a diluent. I n the solution polymerization of vinyl isopropyl ether catalyzed by boron fluoride-diethyl ether and by gallium trifluoride, the chemical nature of the solvent has heen found to be important (IO). A number of halogen-contain-
Vol. 41, No. 12
ing solvents gave smooth polymerization and comparatively high polymers in the temperature range 0 " to 50" C. Although the polyvinyl isopropyl ethers obtained by this method are not so high in viscosity as some of those obtained by polymerization at low temperatures, they are surprisingly high, qspjc = 0.6 to 5.0, considering the temperature range. Solid polyvinyl isopropyl ethers were obtained a t above 0 O C. in solution only by using monomer of especially high purity, by adding only small amounts of catalyst portionwise from dilute solution, and by maintaining relatively even polymerization over a period of 1 to 2 hours. As shown in Figure 1, the polyvinyl isopropyl ethers of highest viscosity were obtained from smooth polymerizations without sharp peaks of temperature rise. The relation of monomer purity, catalyst concentration, and solvent ratio t o viscosity of produrt is shown in Table II for the experiments of Figure 1. FLASH-TYPE PoLYwamATIoiv. One of the most remarkable types of ionic polymerization is the flash-type reaction for preparing rubberlike polyisobutylene and polyvinyl isobutyl ether, dis, covered by Michael Otto and eo-workers (2, 28, 56). Boron fluoride can act upon mixtures of vinyl isobutyl ether and propane at near -50' C. with almost instantaneous formation of rubberlike high polymers in substantially quantitative yield. Peroxidc catalysis has no counterpart to this sudden formation of a polymer of high molecular weight. Even with considerable variation in catalyst concent,ration, temperature, diluent ratio, and method of mixing, so long as the reaction goes off with suddenness, the polyvinyl isobutyl ethers formed are rubberlike and form-stablt, over a wide range of polymer viscosities including nsp/c = 0.3 t o 9.0. The formation of solid rubberlike polyvinyl isobutyl ethers by flash polymerization even in the lorn viscosity range, qsp/c = 0.3 to 0.8, is in contrast to the sirupy, balsamlike character of the polymers of this viscosity range formed in bulk polymerization at higher temperatures. Solid polymers also have been reported from a-methylstyrene by rapid reaction at low temperatures using boron fluoride ( 1 8 , and from the methyl ester of vinyl oxyacetic acid (6). POLYPHASE POLYMERIZATION. This laboratory has studied a type of ionic polymerization in which the catalyst is presrnt as a separate liquid phase and the polymer slowly grows as a solid phase about the catalyst such as boron fluoride etherate. For the lack of a better name this may be called a polyphase or prolifcrous polymerization. By this means solid high polymers are obtained not only from branched alkyl vinyl ethers but also from n-butyl vinyl ether. Although of similar degree of polymerization to the polymers obtained by flash polymerization, the products of the polyphase polymerization are different in properties having a higher degrec of chain regularity and crystallinity. The properties and structures of the isomeric polyvinyl isobutyl ethers have been especially studied in this laboratory (26, 26). The polyphase polymerization is characterized by relativch slow growth of the polymer masses and, a t least in some cases, slow growth of the polymer chain molecules. This was shown iri t,he following experiments.
TABLE11. POLYMERIZATION OF VINYL ISOPROPYL ETHERIN SOLUTION (SEEFIGURE 1)
.Nn
Experiment NO.
"C "-
Times Monomer Distilled
Total Catslvst Usela, Parts BFa T)PP
Solvent iMonomer Ratio
Myliion Parts Monomer
WP/C
a Catalvst solution was 1 Po R F - . fC2Hs\.O in diethyl ether added clroi,wise Ice water bath used for until ~ ~ l y i i i r r i ~ a t ioccurred. oii external cooling of polyiiirrization rlask rt.Jring reaction.
at re,oiila;inter\,ala
December 1949
2893,
INDUSTRIAL AND ENGINEERING CHEMISTRY
One of these, the balsamlike polyvinyl methyl ether, is prepared by bulk polymerization. The solid crystalline type of 60 polyvinyl methyl ether was prepared by activation with a special solvent a t temperaso tures below which controlled polymerization of vinyl methyl ether ordinarily occurs. At near -70" C. a mixture of w 40 a purified vinyl methyl ether, = I chloroform, and liquid propane 5a was treated with boron fluo30 ride-diethyl ether. A smooth, c slow polymerization occurred, giving the new crystallinetype polyvinyl methyl ether, 20 a nontacky solid, containing no chlorine and having a viscosity, q s p l c , near 0.4. From io viscosity data these new solid polyvinyl methyl ethers have degrees of polymerization similar to the balsamlike, sticky 0 10 ZO 30 40 60 60 70 BO SO polyvinyl methyl ethers. CarTIME ( m i n u t e r ) bon tetrachloride was found Figure 1. Polymerization of Vinyl Isopropyl Ether in Solution to have no activating influence comparable to chloroform. To each of a series of Erlenmeyer flasks of 125-ml. capacity OTHER METHODSOF POLYMERIZATION. Other methods of were added 10 grams of cold purified vinyl n-butyl ether, 40 ionic polymerization have been reported-for example, vinyl grams of liquid propane, and 40 grams of dry ice. In each case cyclohexyl ether and other vinyl ethers have been treated with the mixture in the flask was allowed to stand 5 minutes, after boron fluoride in the gas phase to give low polymers (8). Numerwhich 4 separate drops of boron fluoride-diethyl ether were added directly to the cold mixture from a buret cooled nearly to ous attempts have been made in this laboratory and abroad to the tip by dry ice. The flask was placed in a bath at near - 78 O C. obtain homopolymers of high molecular weight from lower alkyl Evolution of carbon dioxide gas from dry ice within the flask vinyl ethers using peroxide catalysts and heating both in bulk and provided agitation. At the end of the desired time the reaction in aqueous emulsion. Under most favorable conditions yields was stopped by adding a quenching mixture of methanol, antioxidant, and ammonium hydroxide. The polymers were dried of sirupy low polymers as high as 75% have been obtained in this at 50" C. and viscosities determined using solutions of 0.20 gram laboratory from vinyl butyl ethers, but the reactions required as per 100 ml. of benzene at 25" e. in an Ostwald-Fenske type of long as 90 hours at 55" C. with 25% persulfate catalyst based on capillary viscometer. The chain lengths of the polyvinyl the monomer weight. n-butyl ether molecule as indicated by v s p / c values were shown to increase with time of reaction (Table 111).
9
*
Ew
ISOMERISM IN POLYVINYL lSOBUTYL ETHERS
The flash-type polymerization using boron fluoride gives rubTABLE111. INCREASE OF DEGREEOF POLYMERIZATION 'WITH berlike tacky polymers, while the slow polyphase-type reaction TIMEO F POLYPHASE POLYMERIZATION OF VINYL n-BuTYL ETHER with boron fluoride-diethyl ether catalyst gives more crystalline, Time of Expt. Reaction, Polymer nontacky polyvinyl isobutyl ethers (26). The experiments deNO. Min. Yield, % ~i.sp/e scribed below were designed to test whether the catalyst chosen 1 2 22 2.4 or the precise conditions of polymerization is the more important 2 5 28 4.5 3 10 39 6.7 factor determining the structure of the polyvinyl isobutyl ethers 4 15 44 7.3
This type of ionic polymerization apparently involves relatively slow chain growth and there is some evidence in this case that the rate of growth diminishes after a chain length corresponding to about q s p l c = 6 to 7 is reached. The polyphase technique seems unique in giving comparatively
Boron fluoride-diethyl ether was added as catalyst to vinyl isobutyl ether-propane mixture a t low temperatures under conditions such that the polymerization occurred in a few minutes, but not so fast as in the flash polymerization. The product more closely resembled the crystalline-type polymer obtained by the slow polyphase-type reaction, although it had some tack and broke down slowly on milling near room temperature. The following values of viscosity were observed after milling this "fast polyphase" polymer for the periods indicated : WP/C
crystalline, well ordered high polymers of the type CH,-?HX, where X is a group large enough greatly to disturb the chain symmetry (R6,26). Polymers from p-isopropenyltoluene giving an x-ray fiber diagram also have been prepared by a slow ionic method (I?'). ACTIVATED IONICPOLYMERIZATION. As previously reported from this laboratory, it has been possible to prepare two types of polyvinyl methyl ether exhibiting structural isomerism (86).
Polyvinyl isobutyl ether (1-30) before milling After 5 minutes' milling After 15 minutes' milling After 30 minutes' milling
6.2 3.8 2.9 2.0
This is a slower breakdown than the rubberlike type of polyvinyl isobutyl ether normally under oes and pressure-sensitive tack was not much enhanced by mifiing The Shore hardness after milling was near 50. It was concluded that boron fluoridediethyl ether favors the formation of the more crystalline polymers, even though the reaction time is reduced to a few minutes.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2894
A second series of polymerization experinients was made as follows: Using boron fluoride diluted with nitrogen as catalyst, two flash-type polymerizations of vinyl isobutyl ether diluted with propane were carried out in such a way that the polymer was observed to form somewhat more slowly in one case than in the other. The slower polymerization in this case gave a polymer of lower viscosity and in smaller yield : R a t e of Polymerization Fast Slow
Experiment L.S. 3209 L.S. 3210
Polymer Yield, % 98 69
WP/C
3.8
0.9
Both polyvinyl isobutyl ethers Fere rubberlike, but the x-ray diagrams of the stretched polymers showed a faint but definite fiber diagram from the slower polymerization. The polyvinyl isobutyl ether obtained by the more typical flash polymerization gave only a halo diagram without trace of fibering or crystallinity. Although the rapid reaction with boron fluoride gives ordinarily rubberlike polymers, it is concluded that detectable differences in structure may also result from changing this rate. Rubberlike polyvinyl isopropyl ethers were prepared by passing a stream of boron fluoride into the monomer diluted with 2 or 4 parts of petroleum ether a t 50 O C. or lower. I n one of these experiments the polymer formed slowly enough to be observed first on the walls of the beaker, after which it quickly filled the beaker and the temperature rose from - 50' to near 0 O C. These experiments gave a rubberlike, tacky product in contrast to harder, nontacky polyvinyl isopropyl ethers obtained by polyphase polymerization during an hour or longer with boron fluoride-diethyl ether as catalyst.
Vol. 41, No. 12
>o R
H
n'
R
A very important factor may be the competition between the double bond of the vinyl ether and the ether oxygen atoms of (a) the vinyl ether and ( b ) the dialkyl ether to supply electrons to the boron fluoride. Vinyl methyl ether may not respond to small amounts of catalyst a t low temperatures because the boron fluoride is used up for association with the polar and exposed ether oxygen atom. The greatest steric effect of shielding of the oxygen atom may be in the vinyl isopropyl ether, where most of the boron fluoride may be directed toward activation of the double bond, Fischer-Hirschfelder models show this more clearly than can be shown in the two-dimensional diagrams that follow:
-
This view is consistent with the fact that the stabilities of the boron fluoride complexes with dialkyl ethers have been reported to be in the following order (3): dimethyl etherate > diethyl etherate > diisopropyl etherate.
The above experiments suggest that both the chemical nature
of the catalyst and the conditions of polymerization can affect t h e arrangement of OR the degree of chain ordering-e.g., groups in d and e positions along t h e chain molecules. POLYMERIZABILITY OF LOWER ALKYL VINYL ETHERS IN RELATION TO STRUCTURE
Five purified vinyl alkyl ether monomers were compared in their tendency to polymerize in bulk and with hydrocarbon diluents with boron fluoride-diethyl ether complex in diethyl ether solution as initiator, and at initial temperatures ranging from - 100" to 0" C. I n these experiments special attention was given t o adding the catalvst in such a way as t o prevent local tcmperature rises which xould give false ideas of actual initiation temperatures. The following series vas indicated beginning with the most readily polymerized : CH-CW
>o
Chain mechanisms for ionic polvmerizations involving catalyst complexes as initiators, followed by propagation and termination processes, have been suggested by Chalmers ( h ) , Williams (34), and Price (20). Mechanisms proposed for cationic polymerization of monoolefinic hydrocarbons have been reviewed by Heiligmann ( 1 1 ) . The following mechanism for vinyl alkyl ethers is used as a basis for discussion: INITI.4TION
H H C : :C H >o
Table IV shows the approximate temperature thresholds above which the vinyl ethers, without special activators, would polymerize readily with boron fluoride-diethyl ether complex in diethyl ether solution as initiator in bulk and in mixture with hydrocarbon diluents. Branching seems to enhance the ease of vinyl alkyl ether polymerization a t low temperatures. Any theory relating the polymeriaability with structure must also explain that the isopropyl group promotes polymerization with boron fluoride etherate catalyst to a greater extent than the isobutyl group. The ease of releasing electrons t o the ionic catalyst may be involved. A structural theory based on the accessibility of the ether oxygen of the vinyl ether monomer is being proposed as follows:
/
R
BFS
--+
+
-H FIB : C : CH
.
">o
(4)
R
P R O P IG.ITION
+
= isopropyl> isobutyl> n-butyl> ethyl> methyl
wI-1 4: C : CH 11 \o
R -H F3B:E:CH
R R
MECHANISMS O F VINYL ALKYL ETHER POLYMERIZ4TION
+
- H H+ n : C : c '
--+
)o R
TERMINATIOX
When boron fluoride-dialkyl ether complex is added to a system containing a vinyl alkyl ether, but essentially no other polar compound, the following reactions may occur:
R
R
BFI
+
>O:BF~ e >o BF, R R H,C=CH i H,C=CH \ >BF, /O
(1)
+
R
R
'
(2)
The first small addition of catalyst may be used up in association with polar impurities and with the ether oxygen atoms of the vinyl alkyl ether (Equation 2). When a critical catalyst concentration is reached, a center or complex capable of initiating chain growth is formed as shown in Equation 4. If a local hot reaction
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1949 TABLEIV.
TEMPERATURE DEPENDENCE OF VINYL ETHER POLYMERIZATION Threshold Temp., C. (Approx.) -30 to -25 -53 t o -50 -80 to -70 Below - 80 Below 100
Vinyl Ether (Unactivated) Methyl Ethyl n-Butyl Isobutyl Isopropyl
-
POLYMERIZATION OF LOWER ALKYL TABLE V. POLYPHASE VINYLETHERS
Relative Amount of Added Catalyst
Polymer Yield, Gram after 5 Min.
Polymer Yield, % per Unit Catalyst
Methyl Vinyl E t h e r 12
2
6
12 2 4
8
1
2
P
d
0
0
n-Butyl Vinyl Ether 0.51 1.58 2.20
2.6 2.6 1.8
Isobutyl Vinyl Ether 0.51 0.85 1.51
2.6 2.1 1.9
Isopropyl Vinyl Ether 0.68 1.23
6.8 6.2
is produced, the rise of temperature may cause dissociation of boron fluoride from the ether oxygen, raising the effective catalyst concentration and causing an autocatalytic or trigger effect characteristic of ionic polymerizations. The activity of FriedelCrafts catalysts in isomerization shows the mobility imparted by their polarizing influences. Thus, the order of effectiveness of a number of metal halides in the racemization of a-phenyl ethyl chloride is similar to their relative activity as ionic polymerization catalysts ( 1 ) . Isomerization of cis- into trans-stilbene has been carried out using as catalyst boron fluoride-diethyl ether ($1). In producing these reactions boron fluoride probably attaches itself to an electron pair of the double bond. In the case of isobutylene polymerization a carbonium ion theory of initiation has been advocated, inasmuch as small amounts of water or other polar compounds have been found to accelerate polymerization under certain conditions (7, 16, 19, SO). Traces of water as a cocatalyst have not been proved necessary for polymerization of liquid isobutylene by boron fluoride and by aluminum chloride a t -80" C. and below, but contact with moist air has been observed to accelerate the polymerizations (IS). I n this laboratory polar impurities, particularly small amounts of dis-. solved water, alcohols, or aldehydes were always found to retard rather than accelerate solution polymerization of lower alkyl vinyl ethers. Polar impurities were removed by thorough washing by water followed by intensive drying over potassium hydroxide, careful distillation, and storage over sodium metal. I n the temperature range above 0' C. water in the vinyl ether uses up the catalyst, impedes polymerization, and may hydrolyze the monomer t o acetaldehyde and alcohol. However, in polymerizations a t -70" to - 1 O O O C. with boron fluoride ethcrates, ice or water could be added with no marked effect upon the rate or character of the products. Vinyl alkyl ethers may require no cocatalyst because the monomer itself contains the polar oxygen atom. However, the flash and polyphase polymerizations here reported were carried out in contact with laboratory air. The definite temperature thresholds found for vinyl alkyl ether polymerization with boron fluoride etherate catalysts suggest that initiation and propagation are the combined result of catalyst and thermal activation. Earlier work on isobutylene polymerization showed no diminution of the rates of polymerization
289s
with lowering temperature (16, 33). More recently Thomas and Arey have reported some indication of slower polymerization of isobutylene a t very low temperatures ($00). CHAINPROPAGATION IN VINYLETHERPOLYMERIZATION. Eley and Pepper have studied the polymerization of vinyl n-butyl ether initiated near room temperature (6). Stannic chloride was the catalyst used for bulk and for solution polymerization in petroleum ether. Catalyst thresholds were found, below which no polymerization occurred and above which reaction was rapid with temperature peaks of 70" to 90" C. resulting. Similar observations have been made in this laboratory supporting a chain mechanism. Eley and Pepper found the degree of polymerization to increase somewhat over periods of 8 to 14 minutes after the start of the bulk reaction near room temperature. In this laboratory dimer and other low polymers have been found to have retarding effects upon the polymerization of vinyl alkyl ethers t o high polymers. I n the introduction of catalyst for the polyphase-type polymerization care must be taken t o avoid local hot reactions giving low polymers which may act as chain terminators, preventing the subsequent formation of high polymers. With purest vinyl alkyl ether monomer under the best conditions there was almost no induction period (see Figure 1). I n the polyphase-type polymerization solid polymer was observed to form quickly after the introduction of a drop of immiscible catalyst and the data of Table I11 show that chain molecule growth continued for 10 minutes or longer. The experiment described below indicates that for the polyphase polymerization the yields a t low conversions are approximately proportional to the amount of added catalyst and to the number of growing polymerization centers. In fact, in some cases each drop of catalyst could be observed to form a separate growing clump of polymer. Table V shows the results of nine separate polyphase-type polymerizations in 125-ml. Erlenmeyer flasks under similar conditions, except that different vinyl ethers and different amounts of catalyst were added. There was used in each experiment a mixture of 10 grams of purified vinyl alkyl ether, 40 grams of liquid propane, and 40 grams of dry ice to maintain a temperature near -78" C. Earlier experiments had indicated the approximate amount of catalyst required for each vinyl ether. The catalyst solution consisted of a mixture of equal volumes of boron fluoridediethyl ether complex with diethyl ether. Each polymerization reaction was stopped 5 minutes after catalyst addition by introducing a quenchin agent containing alkali, antioxidant, methanol, and water. #he catalyst was delivered from a buret iving approximately 0.0068 gram of boron fluoride etherate per %op. Under these conditions a t -78" C. chain growth was not induced in vinyl methyl ether. Vinyl n-butyl ether and vinyl isobutyl ether respond about the same and both give well ordercd polymers having sharp x-ray fiber patterns when stretched. Chain initiation and growth are extremely rapid in vinyl isopropyl ether to give a yield of 100 times the weight of added catalyst after 5 minutes. The data show evidence of a falling off of the rate as ratio of monomer to catalyst is reduced by polymerization. Among the factors favoring chain propagation and high molecular weight products are a continuous supply of pure monomer and enough catalyst to give continuing reaction without autocatalytic heat build-up. Such conditions occur in the polyphase or proliferous reaction where polymer growth occurs about a catalyst drop surrounded by a large supply of vinyl butyl ether in liquid propane. The solution polymerizations of vinyl isopropyl ether in chlorine-containing diluents a t above 0" C. (data of Figure 1) show that comparatively high polymers can be formed a t unexpectedly high temperatures if conditions for prolonged chain propagation are arranged. In fact, the high degree of polymerization of these polyvinyl isopropyl ethers leads one to suspect that in the polymerizations from mixtures apparently a t -50" C. and lower, the actual local seat of the polymerization may be a t considerably higher temperatures. This is further suggested by observations that polymer growth often starts a t a point of higher
2896
INDUSTRIAL AND ENGINEERING CHEMISTRY
temperature, such as a droplet of introduced catalyst, or at a bubble of boron fluoride gas. I n contrast to vinyl polymerization initiated b y free radicals, the ionic polymerization of vinyl alkyl ethers a t low temperatures is little affected by small amounts of antioxidants or by molecular oxygen. Observations in this laboratory seem in harmony with the concept of the growing polyvinyl butyl ether chain containing the ionic catalyst in chemical combination. The catalyst can be removed from the polymer by treatment with methanol or ethanol or by polymer precipitation from hydrocarbon solutions by adding methanol. Eley and Pepper reported cross linking in polyvinyl n-butyl ethers which had been brought to 90' C. in the presence of stannic chloride catalyst. I n polvmerizations near -80' C. with vinyl n-butyl ether, using boron fluoride etherate catalyst, no evidence of cross-linked insoluble products has been observed in this laboratory. However, vinyl isobutyl ether under certain conditions has given partially insoluble products, such as in flash polymerization with undiluted boron fluoride gas and in boron fluoride-diethyl ether reaction carried out t o obtain polyvinyl isobutyl ethers of unusually high molecular weight. Cross linking may occur at the carbon atom bearing the reactive tertiarv hydrogen atom which is absent in polyvinyl n-butyl ether. There seems to be insufficient evidence from which to choose among the various possible modes of chain termination in vinvl ether polymerization. IONIC POLYMERIZATION OF SOME OTHER VlNYL COMPOUNDS
IONIC POLYMERIZATION OF VIVYLMETHYL KETONE. Purified vinyl methyl ketone polymerizes readily on heating, with or without added peroxide catalysts, to give solid products. At room temperature addition of boron fluoridc-diethyl ether to dried purified vinyl methyl ketone caused rapid polymerization, giving balsamlike sticky, brown polymers. When boron fluoride-diethyl ether catalyst was added to vinyl methyl ketone at -78" C. (containing dry ice) there was little reaction until a large amount of catalyst was used. Then a rapid polymerization occurred with foaming caused by evolution of carbon dioxide from the viscous sirup. A solid polymer was isolated. A polyphase polymerization of vinyl methyl ketone was carried out under better control. To a mixture of equal volumes of dry vinyl methyl ketone monomer and dry petroleum ether along with dry ice, boron Buoride-diethyl ether was added in successive small portions. Under these conditions the catalyst formed a second phase. After about 10 minutes a growth of polyvinyl methyl ketone was observed around the catalyst. As the polymer filled the beaker the reaction became more rapid and it was necessary to pour in methanol quickly t o stop the reaction. The reaction mixture was dissolved by adding methanol made alkaline by ammonium hydroxide and containing an antioxidant (0.17 0 AT-p-hydroxyphenyl morpholine). The polyvinyl methyl ketone was precipitated by pouring the solution into excess water. After drying a t 50" C. in vacuum a nontacky solid polymer of light color was obtained.
Vol. 41, No. 12'
I n 300 to 1000 ml. of dry methylene chloride were dissolved lor1 grams of purified N-vinylcarbaeole. To the agitated solution held below room temperature in a closed vessel were added 7 to 10 ml. of catalyst solution in portions at the rate of 5 to 10 ml. per minute. The catalyst solution consisted of 0.10% purified boron fluoride-diethyl ether complex dissolved in methylene chloride When excessive temperature rise was prevented by external cooling, the polymerization reaction, as indicated by heat evolution, could be extended over a period of nearly an hour, during which agitation was continued. To the viscous solution of polyvinylcarbazole resulting, 5.0 ml. of ammonium hydroxide (28%) werr added to destroy the catalyst. The solid white polymer was prrcipitated in granular form by pouring the methylene chloridr solution gradually into rapidly agitated methanol. LITERATURE CITED
Bodendorf, K., and Bohme, €I., Ann., 516, 1 (1936). Poundy, R. H., and Hasche, R. L., U. S. Dept. Commerce, Office of Technical Services, PB 399 (1945). Brown, H. C., and Adams, R. M., J . Am. Chem. SOC., 64, 2557 1942). Chalmers, William, Can. J. Research, 7, 113, 472 (1932), J Am. Chern. Sac., 56, 912 (1934). du Pant de Nemours & Co., E. I., British Patent 574,034 (1945, Eley, D. D., and Pepper, D. C., Trans. Faraday Soc., 43, 112 (1947). Evans, A. G., and Polyanyi, h l . , J . C'hem. Soc., 1947, 252. Fikentscher, H., Gaeth, R., and Schwah, U. S. Dept. Commercv. O.T.S., PB 11,415; Modern Plastics, 24, 162 (February 1947). Fikentscher, H., and Herrle, Modern, Plastics, 23, 157 (November 1945). Grosser, F., General Aniline & Film Corp., U. S. Patent 2,457,661 (1948). Heiligmann, R. G., J . Polymer Sci., 4, 183 (1949). Hersberger, A. B., Reid, J. C., and Heiligmann, R, G., INI). ENG.CHEM.,37, 1073 (1945). Houtman, J. P. W., J. Sac. Chern. I d . , 66, 102 (1847), Kline, G. M., Modern Plastics, 24, 157 (November 1946); I J ~d. Dept. Commerce, O.T.S., PB 33,272 (1946). Mueller-Cunradi, M., and Pieroh, K. (to I. G. Farheriindustrie: , German Patent 745,030 (November 25, 1943). Norrish, R. G. W., and Russel, K. E., Nature, 160, 543 (1947). Xyquist, A. S., and Kropa, E. L. (to American Cyanamid Co.), BritishPatent 574, 141 (1945). OtJto.M., and Mueller-Cunradi, M . (to I. G. Ferhenindustrie), U. S. Patent 2,130,507 (1938). Pleuch, P. H., Polanyi, M., and Skinner H. A., J. Chem SOC.. 1947, 257. Price, C. C., "Mechanisms of Reactions at Carbon-Carbon Double Bonds," p. 112 New York, Interscience Publishers. 1946. Price, C. C,, and Meister, M.. J . Am. Chem. Soc., 61, 2595 (1939). Reppe, W., and Kuehn, E. (to I. G. Farbenindustrie), U. H. Pat,ent 2.098.108 (1937). Reppe, W.;and Po'hlichkng, 0 , (to I, G. Farhenindusbrie). Ibid., 2,104,000 (1937). Ruthruff, 12. F., Division of Petroleum Chemistry, 98th LMeering, AM. CHEM.SOC., Boston, Mass, 1939. Schildknecht, C. E., Gross, S. T.,Davidson, H. R., Lambert. J. hl., and Zoss, A. O., IND. ENG.CHEX.,40, 2104 (1948). Schildknecht, C. E., Gross, S . T., and Zoss, A. O., Ibid., 41, 1998 (1949) Schildknecht, C. E., Zoss, A. O.,and McKinley, Clyde, Ibid.,39, 180 (1947). Shine, W. M., iModcrn PZnstics, 25, 130 (Seatember 1947). Shostakovskii, M. F., and Sidelekovskaya, F. P., J. Gen. (:hem U.S.S.R., 13, No. 6,428 (1943). Thomas, R. M ., and Arey, W. R., Louisiana Seotion, AM. CHEM. SOC., Meeting-in-Miniature, May 14-16, 1948. Thomas, R. M., and Reynolds, H. C. (to Standard Oil Development Co.), U. s. Patent 2,387,784 (1945). Thomas, R. M.,and Sparks, W. J. (to Jasco, Inc.), Ibid., 2,356,128, 1944. Thomas, R. M., Sparks, W. J., Frolich, P. K., Otto, M., ant! Muellcr-Cunradi, M., J. A m . Chem. Soc., 62, 276 (1940). Williams, Gwyn, J . Chem. Soc., 1940, 775. Wislicenus. Johannefi. Ann.. 192. 106 (1878). Zoss, A. O., and Fuller, D. L., U. S. Dept. Commerm, O.T.S.. PB 67,694 (1947). ~
I O X I C POLYMERIZATION O F f ~ - ~ I K Y L P Y R R O L I D O N E ,POlymerl-
zation of vinylpyrrolidone by heating Fith peroxide catalysts has been disclosed in O.T.S. reports from Germany (9). When two drops of cold boron fluoride-diethyl ether were added to 1 gram of freshly purified liquid vinyl pyrrolidone at room temperature, a mild reaction with perceptible evolution of heat occurred. A clear sirup gradually formed which, after 15 minutes passed to a solid polymer soluble in water. To 10 ml. of vinylpyrrolidone dissolved in 30 ml. of petroleum ether at room temperature were added 2 ml. of boron fluoride-diethyl ether, Polymerization occurred with temperature rise to 40 O C. The polymer recovered was a sticky solid a t room temperature. IONIC POLYMERIZATION OF N-VINYLCARBAZOLC. Polymerization of vinylcarbazole has been disclosed using oxvgen-containing as well as Friedel-Crafts catalysts (14, 18). I n this laboratory the following procedure has been found suitable for obtaining high polymers of vinylcarbazole.
RECEIVEDJune 15, 1949. Presented before the Division of Paint, Varnish, and Plastics Chemistry at the 113th Meeting of the AMERICANCHEMICAL SOCIETY. Chiartgo, Ill.
