Ind. Eng. Chem. Prod. Res. Dev. 1904, 23,238-240
230
Bost, H. W.; Yokley, T. A., Jr. U.S. Patent 4216138, 1980. Bost, H. W.; Zuech, E. A. US. Patent 4 140856, 1979. Brady, D. G.; Moberly, C. W.; Norell. J. R.; Walters, H. C. J. Fire Refard. Chem. 1977, 4, 150-64. Brady, D. G. US. Patent 3936416, 1976. Brady, D. G. U.S. Patent 4010 137, 1977. Fleenor, C. T., Jr. U.S. Patent 4253972, 1981. Gay-Lussac, J. L. Ann. Chim. (Paris) 1821, 18, 211-7. Goulding, T.; Orton, M. L. U.S. Patent 4 195 139, 1980. Halpern, Y. US. Patent 4201 705, 1980. Halpern, Y. US. Patent 4 154930, 1979. Kay, M.; Price, A. F.; Lavery, I. J . Fire Retard. Chem. 1979, 6 , 69-71. Marciandl. F. Ger. Offen. 2 839 710, 1977. Mathis, R. D.; Dix. J. S. U.S. Patent 3810882, 1974.
Olsen, J. W.; Bechle, C. W. U.S. Patent 2442706, 1948. Ratz. R. F. W. US. Patent 3 167576, 1965. Ratz, R.; Sweeting, 0. J. J. Org. Chem. 1963, 28, 1608-12. Underwriters Laboratories, Standard for Safety, Tests for Flammability of Plastic Materlals-UL-94, Third Edfflon, April 28, 1982. Tramm, H.; Clar, C.; Kuhnel, P.; Schuff. W. US. Patent 2106938, 1938. Vandersall, H. L. J. Fire Flammability 1971, 2 , 97-140. Waiters, H. C.U.S. Patent 4 155900, 1979. Wren, H. K. U S . Patent 3633463, 1972.
Receiued for review August 31, 1983 Accepted December 12, 1983
Initiation of Emulsion Polymerization by the Redox System: Titanium( III)-Hydroxylamine Robert A. Patslga,' W. Lerdthusnee, and Isam Marawl Department of Chemistry, Indiana University of Pennsylvania, Indiana, Pennsylvania 15705
The redox system TiCI,-hydroxylamine was examined as an initiator for the emulsion polymerization of styrene and other vinyl monomers at 30 OC. Reaction condltions such as emulsifier type, initiator Concentration, and manner of introduction of initiator were optimized for styrene. The cationic emulsifier, dodecyltrimethylammonium chloride, was found to give the highest yields. Also, best yields were achieved by the incremental addition of 0.1-mL volumes of the initiator at 15-min intervals. Other monomers studied were vinyl acetate, methyl methacrylate, acrylonitrile, and isoprene. Vinyl acetate showed behavior similar to styrene and could be polymerized to high (>80%) yield. Methyl methacrylate and acrylonitrile also gave high yields, although much precipitated polymer was obtained. Isoprene gave only an 8 % yield under the same conditions applied to styrene.
Introduction The discovery that the redox reaction between titanium(II1) ion and hydroxylamine is able to initiate vinyl polymerization was first reported by Howard and by Davis et al. (1951). That this system generates the amino radical, NHy, was substantiated by numerous subsequent studies (Seaman et al., 1954; Albisetti et al., 1959; Minisci and Galli, 1965; Izumi and Ranby, 1975) which examined the identity of amine products formed when various organic substrates were present with the redox reaction. The reaction is generally regarded to be Ti3++ HzNOH + H+ Ti4++ HzO + NHz.
-
It is very likely that in acid solution the radical exists in its protonated form, NH3+.. More extensive studies on the use of Ti3+/H2NOHto initiate polymerization were conducted by Kakurai et al. (1966, 1968),who polymerized dilute aqueous solutions of acrylonitrile, methyl methacrylate, styrene, and vinyl acetate. Also, Serre et al. (1981) and Rubio et al. (1981) prepared amino-terminated poly(methy1methacrylate) and poly(methy1acrylate) using this initiator system with dilute aqueous solutions of the monomers. Since the use of emulsifiers would result in the solubilization of monomers of low water solubility and solubilization of the resultant polymers, it would be expected that higher polymer yields and faster rates would result if the use of Ti3+/H2NOHinitiation could be extended to an emulsion system. Reported here are the results of studies conducted for the establishment of optimum conditions necessary for emulsion polymerization of some common vinyl monomers utilizing this redox initiating pair. There should be some value in these studies since the
amine-terminated polymers obtained could have use in block copolymer synthesis. An additional advantage of redox initiation over conventional initiation by thermal breakdown of peroxides is that molecular weight control of the product should be possible.
Experimental Section All monomers, except styrene, were distilled under an atmosphere of argon. Styrene was vacuum-distilled while a slow bleed of argon was maintained. Commercial, reagent grade hydroxylamine hydrochloride and dodecyltrimethylammonium chloride (DTMACl) were used without purification. A sample of DTMACl which was crystallized from ethyl acetate gave identical polymerization results to the uncrystallized. The titanium trichloride used was a 20% aqueous solution as commercially supplied. The exact concentration of titanous ion was determined by titration with dichromate, according to the procedure of Pierson and Gantz (1954). Polymerizations were conducted in a 500-mL threenecked flasked equipped with an argon inlet, motor-driven Teflon paddle stirrer (with shaft passing through a precision ground bushing), and a rubber syringe cap. The syringe cap was fitted with a syringe needle to allow for escape of argon. The polymerization flask was immersed in a constant-temperature bath maintained at 30 f 0.1 "C. Stirring speed was kept between 180 and 200 rpm. Monomer, water, and emulsifier were placed in the flask and argon was allowed to purge the stirred mixture for 20 min prior to addition of the redox initiators. Initiators were introduced by syringe injection. Unless otherwise indicated, the typical polymerization recipe consisted of 100 mL of distilled water, 20 mL of monomer, 1g of emulsifier, and 1.5 mL each of the two components of the redox pair.
0196-4321/84/1223-0238$01,50/0@ 1984 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23,No. 2, 1984 239
Table I. Effect of Emulsifiers on Yield of Polystyrenea polymer run no. Triton X-100, g yield, % 48
59
60
1.00 2.00 4.00
ir
loo 90
2.1 6.5
6.5 ~~
sodium lauryl sulfate, g
33.0 50.5 31.8 dodecyltrimethylammonium chloride, g 6 21 22
1.00 2.00 4.00
12 64 67
1.00 2.00 4.00
75.0 60.7 37.6
?i
!
Initiation: 1.5 mL each of 1.58 M Ti(II1) and NH,OH, 15 injections of 0.1 mL at 15-min intervals.
Y 30
10
I
0.4
0
The concentrations of titanous ion and hydroxylamine were identical and ranged from 0.08 to 1.70 M. Yield of polymer was determined gravimetrically. This was done by adding a few drops of a hydroquinone solution to a 10-mL aliquot of the final latex and then heating the aliquot to constant weight. Correction was made for mass of emulsifier in the sample.
Results and Discussion Styrene was used as the model monomer for which optimum polymerization conditions were established. Emulsifier Type. Polymerization were attempted with anionic, cationic, and nonionic emulsifiers. Table I shows that highest yields were obtained with the cationic emulsifier, dodecyltrimethylammonium chloride. Hexadecyltrimethylammonium chloride proved to be equally effective. Vinyl acetate, the only other monomer examined in the emulsifier study, was able to polymerize to high yield (82%) with either DTMACl or the nonionic emulsifier, Triton X-100. An explanation for the superior yields obtained with DTMACl compared to the more usual anionic emulsifier, sodium dodecyl sulfate (SDS), is that the latter emulsifier complexes the positive titanium ion and, thus, retards or eliminates its reaction with hydroxylamine. We have observed cloudiness formation when 1.5 M Tic& is added to a 1%aqueous solution of SDS. Effect of Initiator Concentration. The concentrations of TiCl, and hydroxylamine in the syringes were varied in order to obtain the value giving the highest yield of polymer. A total volume of 1.5 mL of each initiator component was introduced in 0.1-mL increments at 15-min intervals. The results of these studies are shown in Figure 1. There appears to be no improvement in polymer yield upon increasing the initiator concentration beyond 0.4 M (in the syringes). Having all of the hydroxylamine in the flask and incrementallyinjecting the titanous solution gave slightly lower (by 5-10%) yields. Effect of Injection Interval. The effect on polymer yield when varying the time interval between each 0.1-mL injection of initiators is shown in Figure 2. The polymer yield reaches a maximum value of about 80% when injection intervls are 15 min or greater. A single injection of 1.5 mL each of 0.80 M solutions of initiators gave a poly(styrene) yield of only 4% after 30 min. The ideal injection interval is a compromise between radical wastage due to a very rapid injection rate and long reaction time when injection intervals are large. The need for injection intervals as long as 15 min or more is contrary to what one would expect on the basis of reported rate constants for the titanous-hydroxylamine reaction. Studies performed on simple aqueous systems
I
I
t 0.8
I
I
1
-1.2
I
1I
1.6
INITIATOR CONCCYTRATlON I Y , In 8yrln.o)
Figure 1. Effect of initiator concentration on yield of poly(styrene); [Ti3+]= [H,NOH], 15 0.1-mL injections. loo 90
t
80
70 0
1
60
IYJlCTlOY INTERVAL (mln.)
Figure 2. Effect of injection time interval on yield of poly(styrene); [Ti3+]= [H,NOH] = 0.80 M, 0.1 mL per injection, 1.5 mL total volume; (*) Twenty injections.
give values at 25 "C for the second-order rate constant which range from 23 M-l s-l (Herman and Bard, 1964) to higher values such as 42 M-' s-l (Blazek and Koryta, 1953), 43 M-' s-l (Lingane and Christie, 1967), and 46 M-l s-l (Fischer et al., 1961). Calculation using a rate constant value of 40 M-ls-' gives a first half-life of only 17 s. Thus, an elapsed time of about 4 min between injections should be sufficient to pass through several half-lives of the titanous-hydroxylamine system. I t appears that the emulsion system being used in this study is somehow retarding the reaction between the redox components. A further indication of such a retardation is reflected in the constancy of molecular weights of poly(styrene) obtained as a result of different initiator injection methods. For example, an injection interval of 1min gave polymer with a viscosity average molecular weight of 1.3 X lo5,and an interval of 15 min gave a polymer molecular weight of 1.9 X lo5. A seed polymerization (low frequency to form particles, followed by rapid, 1-min injections) gave a molecular weight in the same range as above, 2.6 X lo5. This behavior suggests some sort of complexation of one or both initiator components, possibly on the surface of the latex particles. A slow but constant release of titanous
Ind. Eng. Chem. Prod.
240
Res. Dev.
Table 11. Emulsion Polymerizability of Monomers Initiated by Ti3+/H,NOHa run no. monomer polymer yield, %
____-
_ _ _ _ I -
__ ___
.
73 76 LC 88 87
styrene acrylonitrile vinyl acetate' methyl methacrylate is0 pre ne
91.3 52 85 lOOb
8.0
a All runs at 30 ' C , 100.0 mL of water, 20.0 mL of monomer, 1.00 g of DTMACI, 1.58 M Ti(II1) and NH,OH, injected through 20 0.1-mL injections at 15-min intervals. Percent yield difficult to determine due to much precipitated polymer. 2.0 g of DTMACl used. Initiator concentration: 0.88 M with 15 0.1-mL injections at lO-min intervals.
ion and/or hydroxylamine form such complexation or adsorption could account for the need for long injection intervals. Continued experiments are being directed at determining the details of the initiation process. Effect of Polymerization Temperature. There appears to be a direct relation between polymer yield and reaction temperature. Emulsion polymerization conducted at 0 "C gave a poly(styrene) yield of 55%; at 30 "C: 77%; and at 60 "C: 85%. All polymerizations were conducted by using 1 g of DTMACl and 15 0.1-mL injections of 1.3 M initiators. Polymerizability of Various Monomers. Using the optimum conditions for styrene polymerization, an attempt was made to polymerize the four monomers: acrylonitrile, methyl methacrylate, vinyl acetate, and isoprene. Styrene is also included for comparison, except that 2.0 mL of initiators was injected in 0.1-mL increments to increase the poly(styrene) yield above 90%. The results of the monomer studies are shown in Table 11. Acrylonitrile gave a very unstable (much preciptate) product which appeared to be composed of tiny particles, indicative of a suspension polymerization. The methyl methacrylate product was very thick but smooth in consistency. Vinyl acetate gave a normal appearing latex, much like that of the styrene system.
1904, 23, 240-245
Summary These studies show that styrene and other common vinyl monomers may be polymerized in an emulsion system using the redox initiating system titanium trichloridehydroxylamine. Cationic emulsifiers give the most satisfactory yield of polymer and the initiators must be introduced incrementally. Styrene could be polymerized to over 90 % yield of latex. Vinyl acetate behaved similar to styrene. The methyl methacrylate product was thick and unstable, while acrylonitrile may not have polymerized by a true emulsion mechanism. Further study will have to be made to optimize polymerization conditions for each monomer type and additional research is needed to determine the initiation mechanism in an emulsion environment. Registry No. TiC13, 7705-07-9; Triton X-100, 9002-93-1; hexadecyltrimethylammonium chloride, 112-02-7;hydroxylamine, 7803-49-8;poly(styrene) (homopolymer), 9003-53-6; poly(acry1onitrile) (homopolymer), 25014-41-9;poly(methy1 methacrylate) (homopolymer), 9011-14-7;poly(viny1acetate) (homopolymer), 9003-20-7; poly(isoprene) (homopolymer), 9003-31-0; dodecyltrimethylammonium chloride, 112-00-5.
Literature Cited Albisetti, C. J.; Coffman, D. D.; Hoover, F. W.; Jenner, E. L.; Mochel, W. E. J . Am. Chem. SOC. 1050, 81, 1489. Blazek, A.; Koryta, J. Collect. Czech. Chem. Commun. 1053, 18, 326. Davis, P.; Evans, M. G.; Higglnson, W. C. E. J . Chem. SOC. 1051, 2563. Dracka, 0.: Fischerova, E. Collect. Czech Chem. Common. Fischer, 0.; 1061, 26. 1505. Herman, H. B.; Bard, A. J. Anal. Chem. 1064, 36, 510. Howard, E. G. U S . Patent 2587 109 (duPont), Sept 4, 1951. Izumi, 2 . ; Ranby, B. Macromolecules 1075, 8 , 151. Kakurai, T.; Iwai, S.; Noguchi, T. Kobunshl Kagaku 1066, 23, 279. Kakural, T.; Sugata, T.; Noguchl, T. Kobunshi Kagaku 1068, 120. Lingane, P. J.; Christie, J. H. J . Nectroanal. Chem. 1067, 13, 227. Minisci, J.; Galli, R. Tetrahedron Lett. 1065, 1879. Pierson, R. H.; Gantz, E. St. C. Anal. Chem. 1054, 26, 1809. Rubio, S.; Serre, J.; Sledz, J.; Schue, F.; ChaD9let-LetOUrneuX, G. Polymer 1081, 22, 519. Seaman, H.; Taylor, P. J.; Waters, W. A. J . Cbem. SOC. 1954, 4690. Serre, B.; Rubio, S.; Siedz, J.; Schue, F.; Chapelet-Letourneux, G. Polymer 1081, 22, 513.
Received for review July 22, 1983 Accepted December 1, 1983
Stereographic Display of Three-Dimensional Solubility Parameter Correlations David L. Wernlck Corporate Research, Exxon Research and Englneerlng Company, Annandale, New Jersey 0880 1
Correlations of solution properties with Hansen's three-dimensional solubility parameter are not adequately displayed in two-dimensional graphs. The need for laborious construction of threedimensional scale models is eliminated by computer simulation and stereographics. Data points are rotated to the desired viewing angle and projected as a stereopair. Levels of the dependent variable (e.g., solubility) are represented by differing plot symbols. Correlations of magnesium nitrate solubility, cellulose acetate solubility and solution viscosity, benzene activity coefficients, tert-butyl chloride solvolysis rates. 9,1Odibromoanthracene fluorescence lifetimes, and activated carbon adsorption equilibria are illustrated.
It has become clear in recent years that one-dimensional solvent parameter scales such as Kosower's 2, Dimroth et al.'s E,, Hildebrand's 6, or dielectric constant cannot adequately correlate the entire range of solvent effects of interest to chemists (Kamlet et al., 1981; Hildebrand et 0196-4321/84/1223-0240$01.50/0
al., 1970). Several workers have therefore proposed two-, thee-, four-, or even five-dimensionalscales based on linear free energy relationships (Kamlet et al., 1981), on factor analysis (Cramer, 1980), or on cohesive energy density concepts (Barton, 1975; Blanks and Prausnitz, 1964). 0 1984 American
Chemical Society
