April, 1949
1313
THEPOLYMERIZATION OF PHENOXYACETYLENE
[CONTRIBUTION FROM THE CHEMISTRY
Acetylenic Ethers. V.
DEPARTMENT OF THE UNIVERSITY OF
CALIFORNIA, LOS ANGELES]
The Polymerization of Phenoxyacetylene
BY THOMAS L. JACOBS
AND
WILLIAM
PENN
TUTTLE,J R . ~
The polymerization of acetylenic compounds other than acetylene itself has been investigated in only a few instances3 although the literature occa\ /"-2 sionally contains a reference to the changes which Equation 1 Formula I these compounds undergo when heated, and a few substituted acetylenes are known to polymerize readily a t room temperature or be lo^.^^^^^^^ Among the latter, acetylenic ethers of the type ROC=CH appear to offer several advantages for a more careful study of the process. Phenoxyacetylene polymerizes spontaneously a t a moderate rate a t room temperature to give first a deep red liquid and finally a hard, shiny, brittle, black solid. The change was shown to be a true polymerization by powdering this solid and extracting it with benzene in which i t is partially soluble. The insoluble residue had the same composition as the monomer. The reaction appears to occur in two stages, involving first a chain reaction to give a linear, conjugated polyene and next a cross-linking step in which the conjugation is broken. The second reaction probably begins soon after the first linear chains are formed and insolubility occurs well before all of the monomer is consumed. It is suggested t h a t the cross-linking may occur by a Diels-Alder reaction and that the polymerization may be represented by the equaselves as precipitated from benzene by petroleum tions shown. The fist stage in the polymerization may be ether had molecular weights of 3000 to 8000 so followed by observing the rate of disappearance of that, within the experimental error, the lowering monomer. Methods of analysis involving the of the freezing point of benzene by a small sample acetylenic hydrogen of phenoxyacetylene or other of partly polymerized phenoxyacetylene was due properties such as ultraviolet absorption were not entirely to monomer. Tables I and I1 record the readily adapted t o the problem, and the determi- data obtained a t 25 and 40". The percentage of nation finally was made by finding the molecular polymerization of each sample was readily calcuweights cryoscopically of samples polymerized lated, and also the rate constants for the gross reunder various conditions. This method was used action. A first order rate equation fits the data by Taylor and Vernong to follow the photopoly- slightly better than a second order one, but the merization of styrene and vinyl acetate in benzene reaction could not be followed much beyond 50% solution. I t was found that the polymers them- completion due to insolubility of the polymer and no choice between first and second order kinetics (1) For t h e fourth paper of this series see Jacobs and Searles, could be made (see Fig. 1). The values of the THISJ O U R N A L , 66, 686 (1944). rate constants are (2) Much of this paper is based upon t h e Ph.D. thesis of \\'illiam Penn Tuttle, Jr., September, 1943. A preliminary report of t h e work was given before the Organic Division of t h e American Chemical Society a t t h e New York Meeting, September, 1942. Dr. Tuttle was killed while hiking in the Sierra Nevada in August, 19-26, (3) T h e literature t o 1941 is summarized by Mark and Raff, "High Polymeric Reactions,'' Interscience Publishers, Inc., h'ew York, N. Y., 1941, pp. 298-316. (4) Butadiyne: Mueller, H d v . Chim. A c t a , 8, 826 (1925): Straus and Kollek, Ber., 69, 1664 (1926). ( 5 ) Haloacetylenes: Nef, Ann., 298, 356 (1897); Lawrir, A m . Chem. J . , 36, 487 (1906); Hofmann and Kirmreuther, Ber., 41, 314 (1908); 42, 4232 (1909); Wallach, A n n . , 203, 88 (1880); Ingold. J . Chem Soc., l2S, 1528 (1924). (6) Cyanoacetylene: Moureu and Bougrand, A n n . chim., ['JJ 14, 47 (1920). ( 7 ) Propatgyl aldehyde: Huttel, Brr., 74, 1680 (1941). ( 8 ) Taylor and Vernon, THIS J O U R N A L , 53, 2527 (1931).
k a t 25a
First order 0.34 X lO-'sec.-' Second order 0.41 X 10-0 sec-1 wt. fraction-'
k
a t 40'
2 . 2 X 10-B see.-' 2 . 6 X 10-6 see.-* wt. fraction-'
From the first order values, the temperature coefficient for the over-all reaction of producing the linear polymer is found to be 4.3 per 10' between 25 and 40' and the total energy of activation is 23 kcal. per mole of monomer. It is interesting that styrene gives a value of 23.3 kcal. from specific rates determined a t 100.5O and 132°.9910 The (Q)Schulz a n d Husemann, Z . Physik. Chcm., 36B, 184 (1937). (IO) Walling, Briggs and Mayo, THISJOURNAL, 68, 1145 (1946)
THOMAS L.JACOBS AND
1314
WILLIAM
PENN
TUTTLE, JR.
Vol. 71
considerable amount of heat is evolved in the reaction. Samples of monomer in an air-bath produced heat faster than i t was conducted away a t temperatures of 55' or .50 above, and sealed samples could seldom be polymerized above 80' without exploding violently. Larger samples exploded as low .40 as 65'. Tables I and I1 also contain the results .70 6 ,+ of a preliminary study on the influence on .30 .60 I the polymerization of typical catalysts and .50 6 inhibitors for vinyl monomers. Most of 9 .50 --. these were ineffective in the concentrations 2 0 .40 .40 used. Among substances expected t o promote ionic polymerization only cadmium .30 .60.30 iodide produced a change, and even with .50 it the catalysis was erratic in a series of .10 2 0 '40 ,20 qualitative experiments. The polymer ob.30 .20 . i o tained appeared to be different from that .10 .10 formed in the absence of the catalyst. Stannic chloride and aluminum chloride 100 200 300 gave no qualitative evidence of catalytic 10 20 30 40 50 60 70 action, but were not tested quantitatively. Time, hr. fi-Toluenesulfonic acid may have been Fig. 1.-Thermal polymerization of phenoxyacetylene a t 25.0 and without effect because it added to the triple bond. 40.0': 0 , first order equation, 25O, inner left-hand scale and inner Iodine was tried because i t is a powerful time scale; 0, second order equation, 25O, inner right-hand scale catalyst for the polymerization of vinyl and inner time scale; @, first order equation, 40°, outer left-hand ethers1' Since i t is known to add to scale and outer time scale; A, second order equation, 40°, outer phenoxyacetylene,12the failure to observe right-hand scale and outer time scale; Ct is wt. fract. of monomer, catalysis is not surprising. The experiment COis original wt. fract. of monomer = 1. with metallic sodium was noteworthy becross-linking reaction made i t difficult to get in- cause when care was taken to bring the phenoxyacetylene into contact with the bright metallic formation about the constancy of chain length. Although no attempts were made to determine surface under an inert atmosphere and with carethe heat of polymerization of phenoxyacetylene, a
