Acknowledgment
The authors express appreciation to C. AI. Frost and L. G. Nickerson for hydrogenating the shale oil and naphtha in preparing the reforming feedstock. We also thank George Miyake for determination of the mass-spectral analysis in the stable reformate. The rrork upon which this report is based was done under a cooperative agreement between the Bureau of Mines, U.S. Department of the Interior, and the University of Wyoming. literature Cited
Carpenter, H. C., Hopkins, C. B., Kelley, R. E., Murphy, W. I. R., Ind. Eng. Chem., 48, 1139-45 (1956).
General Electric (Bethesda, Md.), Time-sharing Service, Program Library Users Guide: Regression Analysis, pp 31-5, February 1968. Hydrocarbon Process., “Reforming,” 47, 155-62 (1968). Mills, G. A,, “Chemical Engineering in Practice,” pp 3-18, Reinhold, New York, N.Y., 1954. Montgomery, D. P., Ind. Eng. Chem. Prod. Res. Develop., 7, 27482 11968) \ - - - - I
Nelson, W. L., “Petroleum Refinery Engineering,” pp 810-18, Maple Press Co., York, Pa., 1964. Ruark, J. R., Sohns, H. W., Carpenter, H. C., “Gas-Combustion Retorting of Oil Shale Under Anvil Points Lease Agreement: Stage 11,” U.S. Bur. Mines Rept. Invest. 7540, 1971. RECEIVED for review May 24, 1972 ACCEPTEDAugust 21, 1972 Presented at the Division of Fuel Chemistry, 163rd Meeting, ACS, Boston, Mass., April 1972.
Radiation-Induced Polymerization of Perfluorobutadiene Madeline S. Toy1 and John C. DiBari Stanford Research Institute, Menlo Park, Calif.9.4025
A study i s made of the radiation-induced polymerization of perfluorobutadiene by use of gamma rays and high-energy electrons. The monomer undergoes 1#2- and 1,4-poIymerizations to yield a solid polymer of molecular weight about 5000.Under the same total dose of radiation, 17.2 Mrad, the molecular weight and polymer yield increase with lower dose rate and longer polymerization period. The bulk and solution polymerizations in aprotic solvents, such as FC-43, FC-75, and n-cehs, are compared under the same dose rate. The presence of solvents increases the yield and changes the relative proportions of 1,2- and 1,4-polymer units, depending upon the polarity of the aprotic solvents. A polar aprotic solvent, such as (n-C4F&N (FC-431, gives a lower yield and larger lower molecular-weight fraction, whereas the nonpolar solvents, such as nC8F18, give a higher ratio of 1,4-polymerization, The content of 1,2-polymer units i s higher in the lower molecular-weight fractions and in the presence of catalyst (5% CFBOOCF,). In the presence of this catalyst, the solvent effect on 1,2- and 1,4-polymerizations i s less pronounced, and the polymer yield becomes higher in the polar solvent. The results are discussed.
Radiation-induced polymerizations of various perfluorodienes and perfluoroolefins were studied a t high pressures (Wall, 1966; Fearn e t al., 1966). T h e polymerizations of perfluorobutadiene under low pressure and ambient temperature were reported to give polyperfluoro-1,2-butadiene and 1,Pbutadiene by use of gamma-ray initiation, ultraviolet light, and in the presence of CF,OOCF, catalyst (Toy, 1970). This paper describes the effects of radiation dose rates, solvents, and catalyst on polymerization of perfluorobutadiene under gamma and electron irradiation. 1
To whom correspondence should be addressed.
404 Ind.
Eng. Chem. Prod. Res. Develop., Vol. 1 1 , No. 4, 1972
Experimental
Perfluorobutadiene and C F 3 0 0 C F 3 (Peninsular ChemResearch) were checked by methods described previously (Toy, 1970; Toy and Newman, 1969; Toy and Lawson, 1968b). The solvents FC-43 and FC-75 (3M), CC1,F (Du Pont), and n-CsFls (Peninsular ChemResearch) were checked by infrared spectra only. The homogeneous liquid samples were placed in evacuated sealed Pyrex tubes under autogenous pressure of about 0.8 a t m before irradiation from external sources a t room temperature. The two radiation sources used were cobalt-60 consisting of 2.5 kilocuries with the dose rate of 0.102 and 0.060 Mrad/
Table 1. Effect of Radiation Dose Rate on Polymerization
Monomer, 4.67 grams Dose Type of irradiation
Product
rate, Mradlhr
Yield, g
Conversion,
%
DP
Molwt
0.0595 1.08* 23.1 5980 37 0.102 0.465* 9.96 4530 28 Electron beam. 4 5 . 9 0.09d 2.89 Liquid Total dose of 17.2 a From cobalt-60 source of 2.5 kilocuries. Ahad. c From 1-MeV (General Electric) electron beam generat,or. d Total dose of 32.5 hlrad. Sample tube was checked at total dose of 17.2 AIrad with no solid product and continued to 32.5 Mrad. Gamma ray.
h r to the total dose of 17.2 ;\had, and a n electron beam from a 1-RIeV (General Electric) electron beam generator whose intensity was 45.9 Mrad/hr to the total dose of 32.5 illrad. The polymerization techniques were described previously (Toy and Xewman, 1970; Toy and Lawson, 1968a). I n essence, a known amount of evacuated monomer in the presence of solvent and/or catalyst of known composition was exposed at ambient temperature and pressure to radiation of known intensity. After irradiation the sealed sample tubes were cooled to solid and opened, and the unconverted monomer was removed through the vacuum system. The polymer samples in the presence of solvents were centrifuged, and the decanted liquids combined with the CC13F extracts from the fractionations of the solid polymers. The combined liquids
were evaporated to dryness and evacuated over anhydrous NgSO4as CC13F-solublefractions. The fractionations of various bulk and solution polymerization samples were carried out by solvent (CC13F) extractions under identical conditions. Results and Discussion
The molecule perfluorobutadiene, unlike butadiene monomer, is nonplanar (Brundle and Robin, 1970), and the minimum energy conformation is cis-nonplanar with a dihedral twisting angle of cis of 47.6" (Chang et al., 1970). Since p-orbitals cannot overlap effectively in a nonplanar conformation, extensive delocalization of perfluorobutadiene monomer is precluded. Table I describes the effect of radiation dose rate on polymerization of perfluorobutadiene to the total dose of 17.2 Mrad by use of gamma rags and high-energy electronb. Under the same total dose of radiation, the molecular weight and polymer yield increased with lower dose rate and longer polymerization period. Only liquid products Lvere obtained at a high radiation dose rate of 45 Mrad/hr. The bulk and solution polymerizations in aprotic solvents such as FC-43, FC-75, and n-C',F1, in the order of decreasiiig dielectric constants (Technical Bulletin, 1965; Simons, 1950), 1.90, 1.86, and 1.79, respectively, are compared in Table 11. This table shows that radical polymerization by irradiation alone can exert some determining action on steric regulation of the polymerization of perfluorobutadiene. The presence of solvents increases the yield and changes the relative proportion of 1,2- and 1,4-polymer units, dependingupon the polarity
Table II. Solvent Effect on Polymerization
Dose rate, 0.0595 bfrad/hr (CO-60 source); total dose, 17.2 M r a d ; solvent, 3 ml; monomer, 4.67 grams After CClaF extraction
-
Solid product Yield, g Conversion,
Solvent
1 08 FC-43a
1 54
FC-75b
1 90
n-C.8'18
1 94
"(n-CaFg)ar\i;mol wt of CC4F
%
Fraction
Yield, g
Wt,
Soluble 0 12 Insoluble 0 96 33 0 Soluble" 1 08 Insoluble" 0 46 40 7 Soluble 0 69 Insoluble 1 21 41 5 Soluble 0 83 Insoluble 1 11 solution fraction (4320) and insoluble fraction (5900). ~ C -CF F I I 23 1
CF.
Ir absorbance ratio, 5 . 6 1 5 . 8 p
%
11 1 88 9 70 1 29 9 36 3 63 7 42 8 57 2
1 1 1 0 1 0 1 0
2 2 8 9 7 3 7 4
CFC,F,
'0'
Table 111. Solvent Effect on Polymerization in Presence of Catalyst
Dose rate, 0.102 ;Llrad/hr (Co-60 source); total dose, 17.2 l l r a d ; solvent, 3 ml; monomer, 4.67 grams After CC13F extraction Solvent
Catalyst
0
0
Solid product Yield, g Conversion,
0 465
9 96
5% C F B O O C F ~
0 60
12 8
n-C8F18
5% CFaOOCF3
0 91
19 5
FC-43"
5% CF300CF3
1.37
29.3
0
%
%
Fraction
Yield, g
Wt,
Soluble Insoluble Soluble Insoluble Soluble Insoluble Soluble Insoluble
0 24 0 225 0 35 0 23 0 19 0.72 0.31 1.06
51 6 48 4 61 7 38 3 20 9 79.1 22.6 77.4
lr absorbance ratio, 5.615.8 p
11 11 11 1 0 1 5 1.1 1.8 1.2
'(n-CIFg)3N.
Ind. Eng. Chem. Prod. Res. Develop., Vol. 11, No.
4, 1972 405
of the aprotic solvent. The influence of the steric structure of the last monomeric unit of the growing chain may indeed play a role in the steric regulation of this radical polymerization process. Solution polymerization in a nonpolar solvent, such as n-CaFls, gives a high proportion of 1,4-polymerizations. The pendant perfluorovinyl bonds (-CF=CF2) from 1,Zaddition polymerization appear a t 5.6 p ; the internal perfluorovinylene bonds (-CF=CF-) from 1,4-addition polymerization appear a t 5.8 p (Toy, 1971). I n Tables I1 and I11 a smaller infrared absorbance ratio (5.6/5.8 p ) indicates more 1,4polymerization. The content of 1,Z-polymer units is higher in the lower molecular-weight fraction (Tables I1 and 111) and in the presence of catalyst (Table 111). Table 111 also shows that the solvent effect on 1,2- and 1,4-polymerizations is less pronounced in the presence of catalyst (50/, CF300CF3),and the polymer yield becomes higher in the polar aprotic solvent ( n - C P d nN.
I n the presence of CFsOOCF3 catalyst (Table 111), the gamma-ray initiation is accelerated by the homolyses of the peroxide bonds to produce C F 3 0 . radicals in pairs. Thus, the polymer initiation depends not only upon gamma rays but also on the fission of the peroxide bonds to produce C F 3 0 . radicals and the subsequent diffusion of radicals to initiate polymerization. The less pronounced effect of 1,Z- vs. 1,4polymerizations owing to polarity of solvents is thus explained by the added initiators and the increase of the polymer yield in polar solvent owing to the homolyses of catalyst to radicals. Literature Cited
Brundle, C. R., Robin, 11.B., paper presented a t 160th ACS Meeting, Chicago, Ill., September 1970. Chang, C. H., Andreassen, A., Bauer, S. H., paper presented at 160th SCS Meeting, Chicago, Ill., September 1970. Fearn, J. E., Brown, I). W., Wall, L. A,, J . Polym. Sci., A - f , 4, 131 il966). \_.__,
Sim&s, J. H., Ed., “Fluorine Chemistry,’’ Vol I, p 441, Academic Press, New York, N.Y., 1950. Technical Bulletin, “Inert Fluorochemical Liquids FC-75 and FC-43.” Minnesota Minine and Manufacturing Co.. St. Paul. Minn.; l?65. Toy, lf.S.,Photochemistry of llacromolecules,” R. F. Reinsch, Ed., pp 135-44, Plenum Press, New York, N.Y., 1970. Toy, hl. S.,Polym. Prepr., Amer. Chem. SOC.,Diu. Polym. Chem., 12 (l), 385 (1971). Lawson, D. D., J . Polym. Sci., B, 6,639 (1968a). Toy, M. S., Toy, AI. S. Lawson, D. D., Polym. Prepr., Amer. Chem. SOC., Diu. Polym. Chem., 9 (a), 1671 (196Sb): Toy, 11.S., Newman, J. hl., J . Polym. Sa., A - i , 7,2333 (1969). Toy, >I, S., Newman, J. AI., Polym. Prepr., Amer. Chem. SOC., Div. Polym. Chem., 11 (l), 121 (1970). Wall, L. A., zbid., 7 (2), 1112 (1966). RECEIVED for review July 17, 1972 ACCEPTED August 19, 1972 I
Conclusions
The polymer yield increases with lower radiation dose rate and longer polymerization period and is greater in solution than in bulk polymerizations. The definite increase of polymer yields in solution polymerizations (Table I1 and 111) can be explained by the increased efficiency of the radicals to diffuse apart in the solvents to interact with the monomer for polymer initiation. The nonpolar solvent n-CsF18 suppresses the competing ionic reactions and thus stabilizes the reactivity of the radicals to give the highest polymer yield shown in Table 11. The relative proportion of 1,4-polymerizations increases d h decreasing polarity of the aprotic solvents. In other words, the 1,4-polymerization is favored in nonpolar solvent.
,
Presented at the Division of Polymer Chemistry, 163rd Meeting, ACS, Boston, Mass., April 1972.
CORRECTION I n the June issue [Ind. Eng. Chem. Prod. Res. Develop., 11 (2), 216 (1972)], Figures 2 and 3 should be interchanged. T h e captions are correct as printed.
406 Ind. Eng. Chem. Prod. Res. Develop., Vol. 1 1 , No. 4, 1972
I
