Letter pubs.acs.org/macroletters
New Class of Alkoxyamines for Efficient Controlled Homopolymerization of Methacrylates Nicholas Ballard,† Miren Aguirre,† Alexandre Simula,† Amaia Agirre,† Jose R. Leiza,*,† José M. Asua,† and Steven van Es*,†,‡ †
POLYMAT and Kimika Aplikatua Saila, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, 20018 Donostia/San Sebastián, Spain ‡ Dispoltec BV, P.O. Box 331, 6160 AH Geleen, The Netherlands S Supporting Information *
ABSTRACT: Despite significant efforts, the design of alkoxyamines for polymerization of methacrylic monomers in a well-controlled fashion with good retention of the active chain ends remains a challenge. Herein, the facile synthesis of several alkoxyamines, which are capable of achieving this long sought-after goal, is reported. Controlled homopolymerization of methyl methacrylate is achieved as determined by a linear increase in molecular weight with conversion and first-order rate plots for various alkoxyamine concentrations. The versatility of the alkoxyamines is further exemplified by the ability to control the homopolymerization of styrene and by synthesis of a block copolymer of a second methacrylate in an efficient chain extension process.
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brium is so much more in favor of the active radical that significant termination occurs, and the reaction can only proceed to low conversion.20,21 By copolymerization with a small amount of styrene, Charleux and co-workers showed that it was possible to control the SG1-mediated copolymerization of MMA.22 The addition of the comonomer substantially lowers the average equilibrium constant and therefore reduces termination. Nevertheless, incorporation of comonomer into the polymer backbone is often undesirable, as it may adversely affect application performance. Using indolinic nitroxides it has been shown that a reasonable level of control over the polymerization of MMA could be achieved,23,24 but the reaction is complicated due to multiple sites of potential decomposition of the alkoxyamines employed. Furthermore, polymerization of monomers other than methacrylates is troublesome with these nitroxides. Similarly, Greene and Grubbs reported the use of alkoxyamines derived from 4-nitrophenyl 2-methylpropionat-2-yl radicals in the effective nitroxide-mediated polymerization of methyl methacrylate but were unable to control the polymerization of styrene with the same nitroxide species.25 Detrembleur and co-workers recently showed that for one specific alkoxyamine generated in situ from a nitroso compound the polymerization progressed without any disproportionation.26 While good control over the molecular weight of the polymer was obtained, in general in situ NMP leads to a complex multicomponent system and somewhat limits precise control over the polymer microstructure.27
n the 1980s, the group at CSIRO undertook pioneering work on the effect of nitroxides on radical polymerization of various monomer systems, which prompted a surge in research into other controlled/“living” radical polymerization techniques.1−4 However, while alternative techniques such as reversible addition−fragmentation chain transfer polymerization (RAFT)5 and transition metal catalyzed “living” radical polymerizations (such as ATRP)6,7 have advanced significantly, the issues that beset nitroxide-mediated polymerization (NMP) from the outset largely still remain. The main drawbacks of NMP are the limited number of monomer families and the need for high reaction temperatures.8,9 The latter problem has been dealt with extensively, and new families of nitroxides have been designed that allow a favorable equilibrium between alkoxyamine end groups and the radicals formed upon their dissociation to be achieved at significantly lower temperatures.10−13 The former problem, however, persists and remains a particular obstacle, especially when compared to transition metal catalyzed radical polymerizations and even more so to RAFT, where the polymerization of a much wider variety of monomers can be successfully controlled.14 One important monomer family that poses a distinct challenge in NMP is that of the methacrylates.15,16 In the early studies on NMP of methacrylates it became clear that an additional nitroxide-induced disproportionation reaction occurred, which resulted in the formation of an unsaturated chain end and termination of the reaction at low conversion.17−19 The development of new nitroxides such as SG1 (N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl) and TIPNO (2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxyl) partly overcame this problem, but a separate issue emerged. With these second-generation nitroxides the equili© XXXX American Chemical Society
Received: July 14, 2016 Accepted: August 11, 2016
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DOI: 10.1021/acsmacrolett.6b00547 ACS Macro Lett. 2016, 5, 1019−1022
Letter
ACS Macro Letters
AIBNgave complex product mixtures due to concomitant formation of MMA by disproportionation (see Supporting Information). Attempts at polymerization using this alkoxyamine synthesized by an alternative route led to termination of the reaction at moderate conversion (see Figure S1 in Supporting Information), as is commonly observed in NMP of methacrylates,17 and no evolution of the molecular weight with conversion was observed. Thus, by virtue of success or failure in the third step, one can predetermine the feasibility of using the targeted alkoxyamine to successfully mediate the polymerization of methacrylates, as the stability of the corresponding nitroxide toward disproportionation is frequently the main issue. The preformed alkoxyamines were used to polymerize methyl methacrylate at 90 °C as a 50 wt % solution in toluene. Linear first-order rate plots were found (see Figure 2), and
In this contribution we report the simple synthesis of a new series of alkoxyamines capable of homopolymerizing methyl methacrylate at moderate temperatures ( I > IV > III. This result is not in exact agreement with the kinetics of polymerizations shown in Figure 2, where the rate of polymerization of alkoxyamine IV is faster than that of alkoxyamine II. This difference may be attributed to differences
Figure 5. Molecular weight distribution of poly(methyl methacrylate) initiated by alkoxyamine IV with [MMA]/[Alkoxyamine] = 100 (filled squares) and molecular weight distribution after chain extension with butyl methacrylate (half filled circles). 1021
DOI: 10.1021/acsmacrolett.6b00547 ACS Macro Lett. 2016, 5, 1019−1022
Letter
ACS Macro Letters
(4) Moad, G.; Rizzardo, E. In Nitroxide Mediated Polymerization: From Fundamentals to Applications in Materials Science; The Royal Society of Chemistry, 2016; pp 1−44. (5) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2005, 58, 379−410. (6) Ouchi, M.; Terashima, T.; Sawamoto, M. Chem. Rev. 2009, 109, 4963−5050. (7) Matyjaszewski, K. Macromolecules 2012, 45, 4015−4039. (8) Nitroxide Mediated Polymerization; Gigmes, D., Ed.; RSC Polymer Chemistry Series; The Royal Society of Chemistry, 2016. (9) Nicolas, J.; Guillaneuf, Y.; Lefay, C.; Bertin, D.; Gigmes, D.; Charleux, B. Prog. Polym. Sci. 2013, 38, 63−235. (10) Benoit, D.; Chaplinski, V.; Braslau, R.; Hawker, C. J. J. Am. Chem. Soc. 1999, 121, 3904−3920. (11) Benoit, D.; Grimaldi, S.; Robin, S.; Finet, J.; Tordo, P.; Gnanou, Y. J. Am. Chem. Soc. 2000, 122, 5929−5939. (12) Cameron, N. R.; Lagrille, O.; Lovell, P. A.; Thongnuanchan, B. ACS Macro Lett. 2012, 1, 1262−1265. (13) Jing, Y.; Mardyukov, A.; Bergander, K.; Daniliuc, C. G.; Studer, A. Macromolecules 2014, 47, 3595−3602. (14) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2012, 65, 985−1076. (15) Guégain, E.; Guillaneuf, Y.; Nicolas, J. Macromol. Rapid Commun. 2015, 36, 1227−1247. (16) Nicolas, J.; Guegain, E.; Guillaneuf, Y. In Nitroxide Mediated Polymerization: From Fundamentals to Applications in Materials Science; The Royal Society of Chemistry, 2016; pp 305−348. (17) Moad, G.; Anderson, A. G.; Ercole, F.; Johnson, C. H. J.; Krstina, J.; Moad, C. L.; Rizzardo, E.; Spurling, T. H.; Thang, S. H. ACS Symp. Ser. 1998, 685, 332−360. (18) Burguiere, C.; Dourges, M.; Charleux, B.; Vairon, J. Macromolecules 1999, 32, 3883−3890. (19) Dire, C.; Belleney, J.; Nicolas, J.; Bertin, D.; Magnet, S.; Charleux, B. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 6333−6345. (20) Guillaneuf, Y.; Gigmes, D.; Marque, S. R. A.; Tordo, P.; Bertin, D. Macromol. Chem. Phys. 2006, 207, 1278−1288. (21) McHale, R.; Aldabbagh, F.; Zetterlund, P. B. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 2194−2203. (22) Charleux, B.; Nicolas, J.; Guerret, O. Macromolecules 2005, 38, 5485−5492. (23) Guillaneuf, Y.; Gigmes, D.; Marque, S. R. A.; Astolfi, P.; Greci, L.; Tordo, P.; Bertin, D. Macromolecules 2007, 40, 3108−3114. (24) Astolfi, P.; Greci, L.; Stipa, P.; Rizzoli, C.; Ysacco, C.; Rollet, M.; Autissier, L.; Tardy, A.; Guillaneuf, Y.; Gigmes, D. Polym. Chem. 2013, 4, 3694−3906. (25) Greene, A. C.; Grubbs, R. B. Macromolecules 2010, 43, 10320− 10325. (26) Detrembleur, C.; Jérôme, C.; De Winter, J.; Gerbaux, P.; Clément, J.-L.; Guillaneuf, Y.; Gigmes, D. Polym. Chem. 2014, 5, 335− 340. (27) Sciannamea, V.; Jérôme, R.; Detrembleur, C. Chem. Rev. 2008, 108, 1104−1126. (28) Grubbs, R. B.; Wegrzyn, J. K.; Xia, Q. Chem. Commun. 2005, 80−82. (29) Zink, M.; Kramer, A.; Nesvadba, P. Macromolecules 2000, 33, 8106−8108. (30) Iwamura, M.; Inamoto, N. Bull. Chem. Soc. Jpn. 1970, 43, 860− 863. (31) Bagryanskaya, E. G.; Marque, S. R. A.; Tsentalovich, Y. P. J. Org. Chem. 2012, 77, 4996−5005. (32) Chauvin, F.; Dufils, P.; Gigmes, D.; Guillaneuf, Y.; Marque, S. R. A.; Tordo, P.; Bertin, D. Macromolecules 2006, 39, 5238−5250. (33) Moad, G.; Solomon, D. H. In The Chemistry of Radical Polymerization, Second ed.; Moad, G., Solomon, D. H., Eds.; Elsevier Science Ltd.: Amsterdam, 2005; pp 49−166. (34) Marque, S.; Le Mercier, C.; Tordo, P.; Fischer, H. Macromolecules 2000, 33, 4403−4410. (35) Souaille, M.; Fischer, H. Macromolecules 2001, 34, 2830−2838.
slightly higher temperature in order to alleviate the broadening of the MWD arising from slow decomposition of the starting alkoxyamine confirmed the ability to produce block copolymers and resulted in polymers with lower dispersity values (see Figure S8). The versatility of these alkoxyamines was confirmed by the well-controlled polymerization of styrene using alkoxyamine IV (see Figure S9). A higher reaction temperature (126 °C) was required to achieve an acceptable rate of polymerization, but both a linear evolution of molecular weight with conversion and a moderate dispersity were observed (Đ ≈ 1.3). Although experimental work is ongoing with alternative monomer families, we believe that the ability to control the polymerization of both styrene and MMA using a single alkoxyamine could prove to be a breakthrough moment in the use of alkoxyamines in controlled polymerization of vinyl monomers. In conclusion, we have demonstrated an efficient synthesis of a new series of alkoxyamines, which are easily scalable and require no time-consuming purification procedures. The alkoxyamines so obtained are capable of homopolymerizing methacrylic monomers without suffering from the usual problems of termination or inadequate equilibrium constant values. Furthermore, the retention of the alkoxyamine chain end allows for synthesis of well-defined block copolymers. It is hoped that the low cost and versatility of the present alkoxyamines will allow NMP to compete more effectively with alternative reversible deactivation radical polymerization techniques.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.6b00547.
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Full experimental details on the synthesis and characterization of alkoxyamines and polymers (PDF)
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Ministerio de Ciencia e Innovación (MINECO, ref. CTQ201459016-P), the Basque Government (GV IT-303-10), Gipuzkoako Foru Aldundia (EXP 55/14), and UFI11/56 are gratefully acknowledged. Miren Aguirre acknowledges the financial support obtained through the Post-Doctoral fellowship Juan de la Cierva en Formación (FJCI-2014-22336), from the Ministry of Economy and Competitiveness of Spain.
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REFERENCES
(1) Solomon, D. H.; Rizzardo, E.; Cacioli, P. Polymerization process and polymers produced thereby. U.S. Patent 4,581,429, 1986. (2) Georges, M. K.; Veregin, R. P. N.; Kazmaier, P. M.; Hamer, G. K. Macromolecules 1993, 26, 2987−2988. (3) Solomon, D. H. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 5748−5764. 1022
DOI: 10.1021/acsmacrolett.6b00547 ACS Macro Lett. 2016, 5, 1019−1022
