CIIARLFS E. SCOTT. \ N D CH.ZRLES C. PRICE
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ylvinylsilanes absorb a t lower wave length and The electrical factors observed for the vinylsilmuch lower intensity than vinyl sulfides. anes seem to be about as expected, intermediate beThese facts suggest that it is misleading to re- tween sulfide ( c = -1.4)l and sulfone (e = 1.2).’ fer to the radical-sulfide resonance interaction as “ d - The more positive e-value for the triethoxy comorbital” resonance. il 3d orbital must be utilized pound could be ascribed to the electron-withdrawin the process but i t appears likely that it must be ing inductive effect of the oxygen atoms as comused to hold the unshared 9th electron on the sulfur pared to the methyl groups of the trimethyl comatom (B). If the double bond in (B) were indeed a pound. 2p-3d double bond, i t could be expected that silicon could participate in such interaction equally SOTRE DAME,I N D well. PHILADELPHIA, PEVNA
[ C O N T R I R U T I O N FROM THE CHEMISTRY
DEPARTMENTS, vXIVERSITY
O F S O T R E DAME A S D [TXIVERSITY OF PENSSYLVASIA]
Divinyl Sulfide : Copolymerization and Spectra B Y CH.4RLE.5
E.SCOTT A N D
CHARLES
c. P R I C E
RECEIT E D DECEMBER 18, 1938 Divinyl sulfide has a very intense absorption in the ultraviolet, A,, 240 and 255, E,,, 41,800 and 38,000. Earlier values are very probably those for the corresponding sulfoxide. The high degree of conjugation is reflected in the polymerization characteristics of divinyl sulfide. The material can be converted to soluble high polymer in 50% yield by azobisisobutyronitrile catalysis. Copolymerization studies indicate the resonance stabilization factor, Q = 0.6 =k 0.1, t o be appreciably higher than that for methyl vinyl sulfide, Q = 0.33.
The similarity of conjugating properties of the vinylene and sulfide groups has been emphasized by many authors.’ The particular case of the similarity of ultraviolet spectra between divinyl sulfide and 1,3,5-hexatriene?has stimulated this further investigation of the conjugative properties of the former. One example of the enhanced conjugation in divinyl sulfide (I) is the increased ease of its conversion to homopolymer, as compared to methyl vinyl sulfide. The fact that the polymer produced after 50y0conversion is still soluble is itself evidence of the greater reactivity of the divinyl sulfide system than of a vinyl sulfide system. Normal vinyl polymerization of I would produce a polymer with pendant vinyl groups.
The data in Table IV indicate the need for great care in using solvents free of peroxide impurities capable of readily oxidizing sulfide groups to sulfoxides. Thus isopropyl vinyl sulfide showed essentially the same Xmax and log Emax in alcohol and in freshly puri$ed dioxane. In dioxane which had been purified earlier and stored without exclusion of air, there was an appreciable shift of the absorption to longer wave length and lower intensity, closely resembling the sulfoxide. The ease of oxidation of the sulfide group by peroxide is also supported by the ineffectiveness of benzoyl peroxide as a catalyst. In many monomer systems, benzoyl peroxide and azoisobutyronitrile are roughly equally effective as catalysts. In divinyl sulfide polymerizations, the former is ineffecIZ C H z z C H -(-CHy-CH-)-, tive, presumably due to its rapid destruction by S reaction with the sulfide group. 1 Copolymerization studies of I (MI) with methyl CH2=CH CHz=CH methacrylate and styrene lend further support to I the through conjugation in I. The resonance parThe presence of these pendant vinyl groups is evi- ameter, Q1 = 0.6 =t0.1, is considerably higher than dent from the ultraviolet spectra of copolymers of I that for methyl vinyl sulfide, Q = 0.35. This sug(Table IV) and from the crosslinking and insolubili- gests an added degree of resonance stabilization for zation of these polymers which occurs on standing. the intermediate free radical from I. The fact that the polymer is not highly crosslinked w C H ~ C H . ++ wCH:CH initially must mean t h a t either double bond in I is j 11 far more reactive in polymerization and copolymeri:S: : S. 1 zation than the pendant double bond in the poly1 mer. This in turn would be most readily explained CH, CH, if the two vinyl groups were mutually activated by +.*CHr CH, NCH~CH mCH2CH conjugation through the sulfur atom. \I I1 :s This through conjugation is clearly supported by :s. * 11 the ultraviolet spectra data on I. It is pertinent I CH=CH? CHCHz. CH=CH, to point out that we now believe that earlier reports of the spectra of I are indeed that of its ~ u l f o x i d e . ~ I n the case of copolymerization, the wavy line (1) See, e x . , (a) A. D. Walsh, Quarf. Revs., 2 , 85 (1948); (b) C. C. would represent the remainder of a growing poly-
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Price and J. Zomlefer. THISJOURNAL, 72, 14 (1950); (c) M. R. Padhje and J. C. Patel, Trans. Faraday S O L . 4, 9 , 1119 (1953). ( 2 ) C. C. Price and H. Morita, T H I SJOURNAL, 75, 4747 (1953). ( 8 ) H. Mohler and J. Sorge, Helv. Chim. Acta, 23, 1200 (1940), give 233 and 275, log E,,, 3.7 and 3.76 (in hexane) as contrasted
-
~
t o our values of 240 and 255, log E,,, 4.62 and 4.58 (in dioxane). T h e shift to longer n a v e length and lower intensity would correspond t o t h a t n-e ohserve for isopropyl vinyl sulfide and its sulfoxide (Table 11’).
DIVINYL SCLFIDES :
June 5, 1959
TABLE I COPOLYMERIZATION OF METHYL METHACRYLATE (M?) WITH DIVISYLSULFIDE (M1)" >fib
0.204 ,402 ,504 ,604
,801
Time, Conver- Softening min. sion, 70 point, " C . 24 8.0 145-150 30 11.0 104-110 22 17.0 120-130 25 9 9 170-178 20 4 u 190
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10.57 12 47 14 31 20.00
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