Notes 935
Vol. 8, No. 6, November-December 1975
I
1 rn?
I
-
J
2
3
'2
G
4
5
6
7
CrOrrotEt'311"3r3e'h3re
Figure 1. Dependence of polymer floc production on the mole percent of 1,2-dibromotetrafluoroethane. Results are average values from two or more experiments run with 300 mm partial pressure of TFE and a 20 min irradiation time. (Mole percent of initiator is calculated relative to total initiator and monomer.)
in the uv below 270 nm14 and would be expected to undergo photodissociation of the carbon-bromine bond under irradiation.8 The presence of air in the reaction chamber did not inhibit the reaction. Wilkus and Wrightlla report that the polymer floc produced in the direct irradiation of TFE showed considerable infrared absorption at 980 cm-l due to the presence of either CF3 groups or cyclic fluorocarbons. In this respect, their product differed from the linear form of poly(tetrafluoroethylene). The polymer floc that was produced when 1,2-dibromotetrafluoroethanewas used as initiator showed no infrared absorption near 980 cm-I and was identical with the published spectrum of linear po1y(TFE)lla and with a spectrum of a sample of linear poly(TFE) powder.15 Analysis by mass spectroscopy of the gas phase during and after the 1,2-dibromotetrafluoroethaneinitiated photopolymerization showed no detectable amounts of cyclic fluorocarbons or other low molecular weight side products. This result is in contrast to the side products reported using other initiators or no initiator.16 The polymer floc produced in these reactions contained about 6% bromine by elemental analysis. After heating the floc a t 60' under reduced pressure for 12 hr, the amount of bromine present was found to be less than 1.5%, and the carbon and fluorine analyses were 22.87 and 15.72%, respectively (Calcd for poly(TFE): C, 24.0; F, 76.0). Upon heating in air, the floc was found to fuse to a clear film above 200°, and after heating to 320' there was a 10% loss in material noted. Other halocarbons were tested as initiators in this reaction: carbon tetrachloride, iodomethane, bromoethane, iodoethane, bromotrifluoromethane, and pentafluoroiodoethane. All of these materials did act as initiators, but the products were oils and no polymer floc was produced with any of these compounds. The introduction of bromine, which reacts rapidly with TFE to produce 1,2-dibromotetrafluoroethane, gave results which were identical with experiments using equal molar amounts of 1,2-dibromotetrafluoroethane. Direct gas phase photolysis of 1,2-dibromotetrafluoroethane in the absence of TFE gives a small amount of oily product, but no floc is formed.
References and Notes (1) (a) Department of Chemistry; (b) Donnelly Mirrors, Inc.
(2) B. Atkinson, Nature (London), 163, 291 (1949); J. Chem. SOC., 2684 (1952).
(3) N. Cohen and J. Heicklen, J. Chem. Phys., 43,871 (1965). (4) B. Atkinson, Experientia, 14,272 (1958). (5) D. G. Marsh and J. Heicklen, J. Am. Chem. SOC.,88,269 (1966). (6) (a) D. Saunders and J. Heicklen, J. Phys. Chem., 70,1950 (1966); (b) J. W. Vogh, US. Patent 3,228,865 (1966); Chem. Abstr., 64, P9839e (1966). (7) R. N. Haszeldine, J . Chem. SOC., 2856 (1949); 3761 (1953). ( 8 ) J. P. Sloan, J. M. Tedder, and J. C. Walton, J. Chem. SOC.,Faraday Trans. 1, 69,1143 (1973). (9) J. M. Tedder and J. C. Walton, Trans. Faraday SOC.,62,1859 (1966). (10) (a) A. N. Wright, Nature (London),215, 953 (1967); (b) D. H. Maylotte, U S . Patent 3,679,461 (1972). (11) (a) E. V. Wilkus and A. N. Wright, J. Polymer Sci., Part A-I, 9, 2097 (1971); (b) A. N. Wright, V. J. Mimeault, and E. V. Wilkus, U S . Patent 3,673,054 (1972). (12) Obtained from Kontes Glass Co., parts K-61240 and K-612500 with appropriate stopcocks and rubber septum adapter. (13) P. Mehnert, Angew. Chem., Int Ed. Engl., 13,781 (1974). (14) Gas phase uv spectrum of 1,2-dibromotetrafluoroethane(at 100 Torr): A270nm = 0.04, A250nm = 0.6, A240nrn = 2.0, A,, below 220 nm. (15) Polymist F-5, Allied Chemical Co. (16) S. V. R. Mastrengelo, US.Patent 3,228,864 (1966); Chem. Abstr., 64, P 19444b (1966).
Polymerization of Methyl Methacrylate with tert-Butyl Hydroperoxide and Metal Acetylacetonates C. J. SHAHANI and N. INDICTOR* Chemistry Department, Brooklyn College, CUNY, Brooklyn, New York 11210. Received April 21, 1975
The decomposition of hydroperoxides catalyzed by metal salts and complexes has been extensively ~ t u d i e d . l -Sever~ al of these studies have used metal a c e t y l a c e t o n a t e ~ . In ~~~-~ the present work, the effect of a small concentration of acetylacetonates on tert- butyl hydroperoxide initiated polymerization of methyl methacrylate in l-chlorooctane medium has been investigated. T o relate this work to that of Osawa e t a1.: Co(II), Co(III), and Cu(I1) catalyzed polymerizations have also been studied in benzene. The decompositon of tert-butyl hydroperoxide catalyzed by Co(I1) and Co(II1) acetylacetonates has been studied in the absence of the monomer as well, in both benzene and l-chlorooctane media.
Experimental Section Chemicals. Methyl methacrylate (Eastman Organic Chemicals) was treated with anhydrous NaZS04 and distilled under vacuum. tert-Butyl hydroperoxide, Wallace and Tiernan, Inc. (Lucidol Division), was purified by distilling away lower boiling impurities (>95% by iodometric titration). 1-Chlorooctane (Aldrich Chemicals, Inc.) was distilled and its purity checked by gas chromatography. Metal acetylacetonates, McKenzie Chemical Corp., were recrystallized from chloroform, and their purity was ascertained from uv spectra. Spectroanalyzed benzene (Fisher Scientific Co.) was used without purification. Kinetics. The reactions were performed using either of two techniques. In one, reactants introduced into Carius tubes were frozen at liquid nitrogen temperatures, evacuated, and degassed through three freeze-thaw cycles, sealed under vacuum, and thermostated. Alternately, reactants were saturated with nitrogen, mixed in a thermostated jacketed reactor under a nitrogen atmosphere, and aliquots taken. Rates of polymerization were measured by gravimetric determination of polymer precipitated with methanol. Hydroperoxide was determined by iodometric titration9 using 0.01 N thiosulfate. A t very low and at very high percent decomposition of hydroperoxide only an upper or lower limit could be determined. Number average molecular weights, M , , were determined viscometrically, using the relationlo = 7.24 x 10-5 f i , o . 7 6 where [q] is the intrinsic viscosity. Viscosities were measured at 30° in benzene.
Macromolecules
936 Notes N m w w
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Vol. 8, No. 6, November-December 1975 Notes 937
r-co
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938
Notes
Macromolecules
icantly affect the rate of polymerization in 1-chlorooctane. However, Cu(acac):! which best catalyzes hydroperoxide In the polymerization of methyl methacrylate in l-chlodecomposition also catalyzes polymerization. The activarooctane initiated by tert- butyl hydroperoxide (t-BHP) in tion energy for the polymerization in the presence of Cuthe presence of several metal acetylacetonates, [M(acac),], (acach is seen to be 12.1 kcal/mol as compared with 19.5 as well as in their absence, conversion of monomer and hykcal/mol in its absence. But, a metal complex which facilidroperoxide decomposition were measured a t 40, 60, and tates hydroperoxide decomposition need not catalyze poly80° as a function of time. The results are shown in Table I merization. Thus, in the Co(I1) acetylacetonate system, alalong with the rates of polymerization (R,) and t-BHP dethough peroxide decomposition is enhanced in the presence composition ( R d ) . The variation of the number average moof the metal, polymerization is actually less than in its ablecular weight, &fn, of the polymer, and the initiator effisence. Osawa et alasbhave studied the t-BHP catalyzed polyciency, f , with the progress of reaction, are also shown. Cu(I1) and Co(I1) catalyze the t-BHP decomposition most merization of methyl methacrylate in the presence of Co(I1) and Co(II1) acetylacetonates in benzene at metal effectively, Mn(I1I) and Co(II1) show intermediate activity, and Al(III), Ni(II), Cr(III), and Mn(I1) do not significantly concentrations -15 times higher than those used in the present work. It was reported that Co(11) had a measurable affect the decomposition. That Cu(I1) salts catalyze hydroperoxide decomposition has long been k n ~ ~ n ,Al~ ~ catalytic , ~ ~ Jeffect ~ ~ on the polymerization rate whereas Co(1II) though in the early stage of the reaction hydroperoxide dehad very little effect. A comparison of these results to ours composition seems to follow a first-order pattern, retardaobtained in 1-chlorooctane suggests that the effectiveness of the metal species may be concentration dependent and tion sets in as the reaction progresses. This may be due to sensitive to solvent. To explore this possibility, the Co(I1) the deactivation of the metal by the decomposition prodand Co(II1) catalyzed systems were studied in benzene. In ucts which may blockI3 the active sites on the metal and an earlier work of Osawa et a1.8a it was seen that in benzene prevent the formation of metal-hydroperoxide comCu(I1) had a much smaller effect on t-BHP decomposition plex. 13-17 Hydroperoxide decomposition could also slow than Co(1I) and Co(II1) acetylacetonates, whereas in 1down if peroxy radicals abstract hydrogen atoms to reform chlorooctane Cu(I1) is the most effective catalyst. To conhydroperoxide molecules. A third possibility is the sofirm this medium effect the Cu(I1) catalyzed polymerizacalled “complexation” of hydroperoxide1s with products of tion was also carried out in benzene. The results of these decomposition. A decrease in the rate of hydroperoxide decomposition experiments in benzene are shown in Table 11. I t is indeed with the progress of the reaction would result in a decreasobserved that the catalytic effect of Cu(acac)Z on t-BHP decomposition also decreased to such an extent that it is ing rate of initiation in accord with the observed increase in the molecular weight of the polymer with reaction time a t a barely noticeable a t 80°, and not a t all a t the lower temperatures. Co(I1) catalyzes t -BHP decomposition and retards given temperature. In the Cu(I1) catalyzed system in 1methyl methacrylate polymerization, as in 1-chlorooctane. chlorooctane, however, the molecular weight is seen to inIt may be safely concluded that catalyst activity is solvent crease with temperature, apparently owing to rapid deplesensitive as well as concentration dependent. tion of t-BHP in the early stage of the reaction. The presA comparison of the polymerization data obtained in the ence of metal complexes generally tends to lower the moabsence of metal in the two solvents indicates a substanlecular weight of the polymer formed due to an increased tially smaller rate in the aromatic solvent. A decrease in aurate of initiation, as well as chain transfer to the metal litoxidation rates in aromatic solvents has been observed gands. Work in this laboratory has shown that several of earliersb and attributed to possible formation of phethe metal acetylacetonates have significant chain transfer nols.5b.20 Another factor which could contribute to the deconstant^.'^ crease in polymerization and autoxidation rates is stabilizaMost of the metal acetylacetonates studied do not signifResults a n d Discussion
Table IV Activation Parameters Metal acetyl acetonate
(Ea) cal cd,
( E a ) o b Sd,
A , x 10-5
kc a1 mol-’
kcal mol-’
0.0209
24.2 10.6
19.5 12.1 19.2 19.6 19.6 19.4 18.1 18.8 19.2 20.0 18.4 17.6 18.1
Ed,
Solvent
kcal mol-‘ (39.Old 11.8
A
X
lom6
~~
None
(1
CU(II)
(1
Al(II1)
(1
cr(111)
n
Ni(I1) Mn(I1) Mn(II1)
fl fl
c 0 (11) c 0 (111) None CO(I1) Co(II1) CU(II)
0
n (1
a 1) h b h
come
n
co(II)c co(III)=
(1
1-Chlorooctane.
1) Benzene.
18.1 18.8 19.6 (40.8) e 17.4
7.29 22.3 15.1
17.7 16.6 18.4 15.4
0.27 5.47 21 .o 2.74
No monomer present.
5.16
13.8 14.1 14.5 25.1 13.4 13.6
In n-octane from ref 30. e From ref 31.
97.9 0.00435 58.3 112 116 86.2 11.7 23.7 59.5 76.9 2.51 2.27 6.74
Vol. 8, No. 6, November-December 1975
Notes 939
also react to give free radical products. The decreased initition of the radicals through K complex formation with the ator efficiency in the presence of active metals could result aromatic snlvent.21J2 The observed trend may be simply a from peroxy radical-metal complexes.28 consequence of faster t-BHP decomposition in l-chloroocVariation of the logarithms of rates of hydroperoxide detane. Saturated hydrocarbon solvents are known to induce composition (&) and polymerization (R,) with reciprocal hydroperoxide d e c o m p o ~ i t i o n . ~ ~ temperature has been utilized to obtain activation energies The initiator efficiencies (f = number of polymer chains and frequency factors for hydroperoxide decomposition initiated per initiator molecule decomposed) shown in Ta( E d , A d ) and polymerization (Ea,A). Table IV shows these bles I and I1 represent effective rather than true initiator data along with E, values calculated from E d , using the efficiencies, since chain transfer has not been taken into acrelation: count in computing these f values. In the presence of metals which catalyze t-BHP decomposition, initiator efficienEa = E, ( E d - E t ) / 2 cy is considerably smaller than in their absence. Initiator efficiency increases in the order: Cu(1I) < Co(I1) < Co(1II) where the activation energy for propagation (E,) and that < Mn(II1) < no metal, Al(III), Ni(II), Mn(I1) < Cr(II1). for termination ( E t ) are considered to have values of 4.7 Osawa et dsb measured t-BHP decomposition rates only and 0 kcallmol, r e s p e ~ t i v e l y .The ~ ~ correspondence bein the absence of the monomer. To observe the effect of the tween the observed and calculated values of E, for metal presence of monomer, rates of decomposition were meacatalyzed systems is not good. A similar trend has been obsured for Co(1J) and Co(II1) catalyzed systems in the abserved by Osawa et al.8b who suggest that E, and E t values sence of the monomer in benzene as well as in l-chloroocmay be different in these systems. The observed discrepantane. The data obtained are presented in Table 111. A comcy could also be due to a significant wastage of the initiator. parison with hydroperoxide decomposition data obtained in the presence of monomer (Tables I and 11) shows a sigReferences and Notes nificant acceleration in the absence of monomer. Free radiE. T. Denisov and N. M. Emanuel, Russ. Chem. Reu. (Engl. Transl.), cal addition to the monomer competing with the radical in29.645 (1960). duced decomposition of the hydroperoxide could lead to R.’Hiatt, TI Mill, and F. R. Mayo, J . Org. Chem., 33,1416,1430 (1968). R. Hiatt in “Organic Peroxides”, Vol. 11, D. Swern, Ed., Wiley-Interthis result. Metal-monomer K complex formation may also science, New York, N.Y., 1971, p 1. decrease the activity of the metal, decreasing the rate of N. Indictor and W. F. Brill, J.Org. Chem., 32,2074 (1965). hydroperoxide decomposition. (a) N. Indictor and T. Jochsberger, J . Org. Chem., 31,4271 (1966); (b) N. Indictor, T. Jochsberger, and D. Kurnit, ibid., 34,2855,2861 (1969); In the present experiments, uv spectra showed that (c) T. Jochsberger. D. Miller, F. Herman, and N. Indictor,.ibid., 36, Co(I1) is immediately oxidized to Co(II1) upon contacting 4078 (1971). t-BHP, and throughout the course of the reaction Co(II), if Chim. Fr., 3926,3930 (1966). R. Lombard and J. Knopf, Bull. SOC. present, was below a detectable amount. None of the other N. Indictor and C. Linder, J. Polym. Sci., Part A, 3,3668 (1965). (a) Z. Osawa and T. Shibamiya, J . Polym. Sci., Part B, 6. 721 (1968); metal systems which catalyzed t -BHP decomposition, viz., (b) Z. Osawa, T. Shibamiya, and T. Kawamata, J. Polym. Sci., Part Cu(II), Mn(III), and Co(III), showed change in oxidation A-I, 8, 1957 (1970); (c) Z. Osawa, K. Kobayashi, and Y. Ogiwara, J . state. This suggests that possibly a mechanism which does Mucromol. Sci., Chem., 6,1665 (1972). J. P. Wibaut, H. B. van Leeuwen, and B. van der Wal, R e d Trau. not involve change in the oxidation state of the metal may Chim. Pays-Bas, 73,1033 (1954). be involved. Berger and BickellZb, G o ~ d o t and , ~ ~ other P. Ghosh and F. W. Billmeyer, Jr., Adu. Chem. Ser., No. 91, 75-93 worker^^^-^^ have proposed such mechanisms to account for (1969). M. S. Kharash and A. Fono, J. Org. Chem., 23,324 (1958). the formation of oxygen stoichiometrically. The mecha(a)M. S. Kharash and A. Fono, J. Org. Chem., 24,72 (1959); (b)H. Bernisms involve either ligand displacement,lZbimprobable in ger and A. F. Bickel, Trans. Faraday SOC.,57, 1325 (1961); (c) J. K. view of the high stabilities of the acetylacetonate comKochi, Tetrahedron, 18,483 (1962). plexes of or tetracoordinate complexes of metals (a ) W. H. Richardson, J. Am. Chem. SOC.,87,247, 1096 (1965);(b) W. H. Richardson, J. Org. Chem., 30,2804 (1965); (c) W. H. Richardson, J . capable of assuming hexacoordinate c o n f i g u r a t i ~ n ~by ~-~~ Am. Chem. SOC.,88,975 (1966). accepting two peroxide molecules as ligands. The metal A. J. Chalk and J. F. Smith, Trans. Faraday SOC.,53, 1214, 1235 serves to increase the probability of reaction and assists in (1957). D. Benson and L. H. Sutcliffe, Trans. Faraday Soc., 55,2107 (1959). electron transfer. The metal itself does not undergo any M. L. Kremer, Nature (London), Suppl., 184,720 (1959). redox reaction. Among acetylacetonate complexes studied Y. Kamiya, S. Beaton, A. LaFortune, and K. U. Ingold, Can. J . Chem., here, those of Co(I1) and Cu(I1) are the only ones which are 41,2020, 2034 (1963). (a) E. T. Denisov, Russ. J. Phys. Chem (Engl. Transl.), 37, 1029 (1963); tetracoordinate but are capable of bonding to two more li(b) V. L. Antonovskij and V. A. Terent’ev, Zh. Org. Khim., 3, 1011 gands. Since Co(I1) is oxidized to Co(II1) in the presence of (1967). t-BHP it must assume an octahedral configuration by C. J. Shahani and N. Indictor, manuscript in preparation. K. U. Ingold, Chem. Reu., 61,563 (1961). bonding to two t-BHP ligands. In- the case of t h e Cu(I1) (a) G. A. Russell, J.Am. Chem. SOC.,79,2977 (1957); (b) G. A. Russell, complex, the driving force for the attainment of an octaheibid., 80, 4987, 4997, 5002 (1958); (c) G. A. Russell, J. Org. Chem., 24, dral configuration would be the stabilization obtained in 300 (1959);(d) G. A. Russell, Tetrahedron, 8,101 (1960). C. Walling and M. F. Mayahi, J. Am. Chem. SOC.,81,1485 (1969). this configuration from Jahn-Teller distortion. It must be J. R. Thomas and 0. L. Harle, J. Phys. Chem., 63,1027 (1959). pointed out that some of the metal catalyzed t-BHP deA. Goudot, C.R. Hebd. Seances Acad. Sci., 250,346,712 (1960). composition does seem to take place through a radical M. Seigel, Angew. Chem., Int. Ed. Engl., 8,167 (1969). Z. Kovats, Mag. Kem. Poly. 69,98 (1963). mechanism, since an increased rate of t-BHP decomposiChem. Soc., Spec. Publ., No. 6,29 (1957). tion does result in an increased rate of initiation, as indiA. Tkac, K. Vesely, and L. Omelka, J . Phys. Chem., 75. 2575, 2580 cated by the observed decrease in molecular weight of the (1971). Z. A. Sinitayna and Kh. S. Bagdasarayan, Zh. Fiz. Khim., 32, 1319 polymer formed. The observed result can also be explained (1958). by a reaction path which would involve coordination of two E. R. Bell, J. H. Raley, F. F. Rust, F. H.Seubold, and W. E. Vaughan, t-BHP ligands to Cu(I1) or Co(I1) acetylacetonate, as sugDiscuss. Faraday SOC.,10,242 (1951). R. Hiatt and W. M. J. Strachan, J . Org. Chem., 28,1693 (1963). gested above, with the difference that these ligands may
+
