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Langmuir 2003, 19, 6342-6345
Letters Grafting Poly(n-butyl acrylate) from a Functionalized Carbon Black Surface by Atom Transfer Radical Polymerization† Tianqi Liu, Shijun Jia, Tomasz Kowalewski, and Krzysztof Matyjaszewski* Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213
Rosa Casado-Portilla and James Belmont Cabot Corporation, 157 Concord Road, Billerica, Massachusetts 01821-7001 Received February 8, 2003. In Final Form: May 5, 2003 The functionalization of a carbon black surface with atom transfer radical polymerization (ATRP) initiating sites and subsequent ATRP of n-butyl acrylate (n-BA) from the surface of carbon black is reported. The polymerizations were carried out using CuBr/N,N,N′,N′,N′′-pentamethyldiethylenetriamine and CuBr2/ 4,4′-di(5-nonyl)-2,2′-bipyridine as the catalytic system at 70 °C. A significant amount of polymers was attached to the carbon black as determined by thermogravimetric analysis and light scattering experiments. The molecular weights of the polymers grafted on carbon black were determined by detachment experiments and measured by gel permeation chromatography. The presence of dense poly(n-BA) brushes around carbon black aggregates was confirmed by atomic force microscopy. The resulting poly(n-BA)-bound carbon blacks formed stable dispersions in organic solvents for poly(n-BA).
Carbon black is composed of primary particles with diameters of 10-75 nm that are fused into aggregates that range from 50 to 500 nm in size. It is widely used in the rubber industry as a reinforcing agent and in the plastics industry for its antistatic, conductive, and UVprotective capacities.1-4 It is also an important pigment used for coatings,5 plastics,1,3 packaging,6 ink,7 and inkjet8,9 and toner applications.10,11 These applications involve dispersing carbon black into either polymeric systems or solvents. The control over interfacial properties of these materials is of great importance and still remains a challenge. It has been found that the dispersibility of carbon black in resins and solvents can be significantly improved by grafting polymers onto the surface of carbon black.12,13 †
Part of the Langmuir special issue dedicated to David O’Brien.
(1) Donnet, J. B.; Bansai, R. C.; Wang, M. J. Carbon Black: Science and Technology, 2nd ed.; Marcel Dekker: New York, 1993. (2) Wolff, S.; Wang, M. J. In Carbon Black, 2nd ed.; Donnet, J. B., Bansal, R. C., Wang, M. J., Eds.; Marcel Dekker: New York, 1993; p 289. (3) Funt, J. M.; Sifleet, W. L.; Tomme, M. In Carbon Black, 2nd ed.; Donnet, J. B., Bansal, R. C., Wang, M. J., Eds.; Marcel Dekker: New York, 1993; p 389. (4) Donnet, J. B.; Voet, A. Carbon Black: Physics, Chemistry, and Elastomer Reinforcement; Marcel Dekker: New York, 1976. (5) Li, W.; Xie, Z.; Li, Z. J. Appl. Polym. Sci. 2001, 81, 1100. (6) Chi, A. Y. Pop. Plast. Packag. 1998, 43, 57. (7) Belmont, J.; Adams, C. U.S. Patent 5,713,988, 1998. (8) Belmont, J.; Johnson, J.; Adams, C. U.S. Patent 5,630,868, 1998. (9) Belmont, J.; Johnson, J.; Adams, C. U.S. Patent 5,571,311, 1996. (10) Hisashi, H. Kino Zairyo 2000, 20, 42. (11) Julien, P. C. In Carbon Black, 2nd ed.; Donnet, J. B., Bansal, R. C., Wang, M. J., Eds.; Marcel Dekker: New York, 1993; p 409. (12) Ikeda, H.; Urashima, N.; Ando, N. European Patent Application 987303, 2000. (13) Tsubokawa, N.; Satoh, T.; Murota, M.; Sato, S.; Shimizu, H. Polym. Adv. Technol. 2001, 12, 596.
Two methods are generally used to form covalent polymer-bound carbon black hybrids: “grafting from” and “grafting onto”. “Grafting onto” involves the reaction of reactive macromolecules with surface groups. Initially attached polymers, however, hinder the approach of other polymers, leading to a limited density and coverage. “Grafting from” involves surface initiation and subsequent polymer growth from the surface. It usually affords a higher grafting density due to the much higher diffusion rate of small molecules (i.e., monomers) compared to polymers. Anionic,14,15 cationic,16-18 and radical19-21 graft polymerizations onto carbon black have been investigated. Radical polymerizations can tolerate many functional groups and can be performed under mild conditions. Since carbon black is known to be a strong radical scavenger due to the presence of polycondensed aromatic rings and quinonic and phenolic oxygens, propagating polymeric radicals can be easily trapped by carbon black surfaces during polymerization. Preformed polymers can also be grafted onto carbon black if they can dissociate and form radicals. Tsubokawa and co-workers22 synthesized TEMPO-terminated polystyrenes with controlled molec(14) Tsubokawa, N. J. Macromol. Sci., Chem. 1987, A24, 763. (15) Tsubokawa, N.; Tsuchida, H.; Kobayashi, K. Nippon Gomu Kyokaishi 1993, 66, 124. (16) Tsubokawa, N.; Takeda, N.; Kanamaru, A. J. Polym. Sci., Polym. Lett. Ed. 1980, 18, 625. (17) Tsubokawa, N.; Takeda, N.; Kanamaru, A. Carbon 1980, 18, 378. (18) Tsubokawa, N.; Jian, Y.; Sone, Y. J. Polym. Sci., Part A: Polym. Chem. 1988, 26, 2715. (19) Hayashi, S.; Handa, S.; Tsubokawa, N. J. Polym. Sci., Part A: Polym. Chem. 1996, 34, 1589. (20) Hayashi, S.; Naitoh, A.; Machida, S.; Okazaki, M.; Maruyama, K.; Tsubokawa, N. Appl. Organomet. Chem. 1998, 12, 743. (21) Tsubokawa, N.; Fujiki, K.; Sone, Y. Polym. J. 1988, 20, 213.
10.1021/la034219d CCC: $25.00 © 2003 American Chemical Society Published on Web 05/31/2003
Letters
Langmuir, Vol. 19, No. 16, 2003 6343 Scheme 1. Functionalization of Carbon Black
ular weights and low polydispersities and grafted them onto carbon black by thermal dissociation of a C-ON bond followed by trapping of the polymeric radicals by carbon black. Despite the advantage of grafting well-defined polymers onto carbon black, the percentage of grafting was low (
