395
DIRADICALS IN SOLUTION
Jan. 20, 1954
separate binodal curves has been observed in the author's laboratory.* These involve liquid carbon dioxide and will be presented in a later paper. They include also several examples of ternary systems with three separate binodal curves on the
16.0
27.0
Col
16.0 12.0 4.0 0
27.0 25.0 21.0 79.7 70.9 48.3 32.9p.p." 27.7 20.2
16.0 30.0 0 15 72.0 4.7 9 59.8 12.8 15.3 50.9 TABLE I1 11.8 22.5 37.2 SYSTEMMETHANOL-NITROBENZENE-ISO~CTANE (WEIGHT 10.1 24.8 30.8 PERCENTAGES) 19.2 0 21.8p.p. Temp., 20.3 14.9 Methanol Nitrobenzene OC. Methanol Nitrobenzene 6.0 8.0 77.0 8.0 92.0 0 0 7.0 0 17.0 0 85.9 55.7 20 0 76.2 69.6 0 (Equil. with solid 40.3 29.0 3.7 68.7 53.8 9.7 nitrobenzene) 27.3 45.5 7.4 57.5 46.1 13.9 4.5 0 25.5 48.2 7.5 45.5 32.0 19.3 4.7 16.1 7.0 60.6 7.0 41.4p.p. 28.8 20.9 4.5 5.2 8.4 78.1 6.4 38.4 21.9 18.6p.p. 14.3 3.8 0 86.1 9.8 3.2 28.5 5.8 12.2 0 7.5 0 0 23.8 74.2 0 10 0 25 0 73.5 66.6 62.1 9.5 5.0 0 7.9 3.5 60.0 52.3 3.9 6.5 24.5 40.3 37.7 12.8 3.3 47.9p.p. 9.7 32.1 32.2 7.5 24.5 13.4p.p. 0 34.2 14.8 21.1 42.4 8.7 8.9 14.8 17.4 16.8 51.0 3.7 11.4 4.9 16.0 11.8 60.8 0 8.0 0 74.0 4.9 53.0p.p. 29.65 0 0 83.0 (also C.S.T.) 23.5 27.1 8.5 14 9.5 42.6 33.6 0P.P. 18.0 12.0 27.2 18.2 (also C.S.T.) 18.0 22.8 11.3 32.3 Plait points, P.p. 14.2 24.8 10.3 47.0 19.5 0 three sides of the triangular diagrams, a novel phenomenon. Practical uses for some of these 20.0 22.0 27.0 14.1 13.0 systems are shown. 15.0 25.0 (8) A. W.Francis, U. S.Patents 2,631,966 and 2,646,387 (1953). PAULSBORO, N. J. [CONTRIBUTIONFROM THE FRICK CHEMICAL LABORATORY, PRINCETON UNIVERSITY ]
Diradicals in Solution : Role in Polymerization BY K. E. RUSSELL AND A. V. TOBOLSKY RECEIVED JULY 27,1953 Diradicals have been produced by the photolysis of 1,4,5-oxadithiacycloheptane. A minimum value for their rate of formation in benzene solution is given by the rate of disappearance of 2,2-diphenylpicrylhydrazyl. I n methyl methacrylate the great majority of the diradicals either undergo primary recombination, or form small rings after the addition of one or two monomer units. Few, if any, of the diradicals grow t o form long polymer chains. The photolysis of butyl disulfide has been investigated so that comparisons can be made with a disulfide source of monoradicals. The photodecomposition of the transannular peroxide ascaridole has been shown to lead t o monoradicals.
Introduction For many years i t has been considered that the thermal and photopolymerization of styrene proceed by way of diradical intermediates. Floryl suggested that initiation of thermal polymerization involves the reaction P
IH=cHg
+ cIH = c H a
-+
v
P
.CH-cH2-cH-cH2. I I
and that photopolymerization is initiated by the opening up of the carbon-carbon double bond of a single monomer molecule to give a diradical. (1) P. J. Flory, THISJOURNAL, 59, 241
(1937).
Recently the role of diradicals in these types of polymerization has been q ~ e s t i o n e d . ~It . ~ has been shown that if diradicals are formed in the initiation reaction, they are unlikely to grow to long polymer chains but have a high probability of undergoing self-termination to form small rings.3 I n photopolymerization the relationship between the molecular weight of the polymer isolated and the rate of polymerization leads to the conclusion that long chain photopolymer is formed from growing monoradicals2; no evidence was found that thermal polymer is formed from growing diradicals.2 (2) D. H. Johnson and A. V. Tobolsky, { b i d . , 74, 938 (1952). (3) B. H. Zimm and J. K.Bragg, J . Polymer Sci., 9, 476 (1952)
396
K. E. RUSSELLAND A. V. TOBOLSKY
It is clear that new studies are necessary in order to determine the role of diradicals in thermal and photopolymerization. A positive method for the production of diradicals is required so that a technique for following their actual rate of formation can be developed; the method would also allow the direct study of the reactions of diradicals in monomer solution and would give information on the occurrence of ring formation. With such knowledge it is possible to re-examine the problems of thermal and photopolymerization and to shed considerable light on the reactions involved. Experimental Methyl methacrylate, from the Rohm and Haas Co., was freed from inhibitor by shaking twice with 5% sodium hydroxide solution, and washed three times with distilled water. I t was dried over potassium carbonate, and distilled in an atmosphere of nitrogen a t a pressure of 90 mm., a middle fraction with a b.p. range of 0.2' being collected. I t was used immediately after distillation. 2,Z-Diphenylpicrylhydrazylwas a gift from Dr. I
