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| Untersuchte Arbeit: Seite: 52, Zeilen: 3-6, 8-16 |
Quelle: Hawker 2002 Seite(n): 477, 478, Zeilen: 477:(32-33).33-38; 478:6-12.14-18 |
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| The Xerox group made the first attempts to develop a new better system which relied on the use of nitroxides other than 2,2,6,6-tetramethylpiperidinoxy (TEMPO). They have polymerized acrylates at elevated temperatures (145 - 155 °C) in the presence of 4-oxo-TEMPO, as the mediating nitroxide.
However the polidispersities [sic] were still between 1.40 - 1.67 and the living nature of the polymerization was questionable [Keo98]. [...] The most [sic] breakthrough in the design of improved nitroxides was the use of alicyclic nitroxides, which bear a structural resemblance to TEMPO. In fact, their most striking difference was the presence of a hydrogen atom on one of the α-carbons, in contrast to the two quaternary α-carbons present in TEMPO and its derivatives. The best examples of these new materials are the phosphonate derivative, 1, 3 introduced by Gnanou and Tordo [Ben00, Mat95a] and the family of arenes 2, 4, 5 presented by Hawker [Ben99, Har01] (Scheme 2 - 15). The new initiators such as 1 and 2 permit the polymerization with high control of molecular weights and polydispersities as low as 1.06. [Ben99] Benoit, D.; Chaplinski, V.; Braslau, R.; Hawker, C. J. J. Am. Chem. Soc. 1999, 121, 3904. [Ben00] Benoit, D.; Grimaldi, S.; Robin, S.; Finet, J. P.; Tordo, P.; Gnanou, Y. J. Am. Chem. Soc. 2000, 122, 5929. [Har01] Harth, E.; van Horn, B.; Hawker, CJ. Chem. Commun. 2001, 823. [Keo98] Keoshkerian, B.; Georges, M. K.; Quinlan, M.; Veregin, R.; Goodbrand, R. Macromolecules, 1998, 31, 7559. [Mat95a] Matyjaszewski, K.; Gaynor, S.; Greszta, D.; Mardare, D.; Shigemoto, T.; Wang, J.-S. Macromol. Symp., 1995, 95, 217. |
[page 477]
Initial efforts to develop new mediating nitroxides relied on TEMPO-based derivatives. The Xerox group were able to polymerize acrylates at elevated temperatures (145–155°C) in the presence of 4-oxo-TEMPO, 33, as the mediating nitroxide, and while this is a significant improvement when compared to TEMPO, polydispersities were still between 1.40 and 1.67 and the living nature of the polymerization was questionable.47 [page 478] The most significant breakthrough in the design of improved nitroxides was the use of alicyclic, nonquaternary nitroxides. These materials bear no structural resemblance to TEMPO, and their most striking difference was the presence of a hydrogen atom on one of the α-carbons, in contrast to the two quaternary α-carbons present in TEMPO and all the nitroxides discussed above. The best examples of these new materials are the phosphonate derivative, 35, introduced by Gnanou and Tordo52 and the family of arenes, 36, introduced by Hawker (Fig. 10.3).53 [...] The use of nitroxides such as 35 and 36 now permits the polymerization of a wide variety of monomer families. Acrylates, acrylamides, 1,3-dienes, and acrylonitrile-based monomers can now be polymerized with accurate control of molecular weights and polydispersities as low as 1.06.54 47. B. Keoshkerian, M. K. Georges, M. Quinlan, R. P. N. Veregin, and R. Goodbrand, Macromolecules 31, 7559 (1998). 48. K. Matyjaszewski, S. Gaynor, D. Greszta, D. Mardare, and T. Shigemoto, Macromol. Symp. 95, 217 (1995). 52. D. Benoit, S. Grimaldi, S. Robin, J. P. Finet, P. Tordo, and Y. Gnanou, J. Am. Chem. Soc. 122, 5929 (2000). 53. D. Benoit, V. Chaplinski, R. Braslau, and C. J. Hawker J. Am. Chem. Soc. 121, 904 (1999). 54. D. Benoit, E. Harth, P. Fox, R. M. Waymouth, and C. J. Hawker, Macromolecules 33, 363 (2000). 86. E. Harth, B. van Horn, and C. J. Hawker, J. Chem. Soc. Chem. Commun. 823 (2001). |
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