Macromolecules 1995, 28, 7572-7573
7572
“Living”/Controlled Radical Polymerization. Transition-Metal-Catalyzed Atom Transfer Radical Polymerization in the Presence of a
Table
[AIBNlo [CuCl2]o [bpylo time (mol/L) (mol/L) (mol/L) (h)
Conventional Radical Initiator
0.023 0.034 0.025 0.018 0.0091 0.0065
Jin-Shan Wang and Krzysztof Matyjaszewski* Department of Chemistry, Carnegie-Mellon University, 4400 5th Avenue, Pittsburgh, Pennsylvania 15213
Received June 20, 1995 Revised Manuscript Received September 1, 1995
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Characterization
1.
Data of Styrene Bulk
Polymerization Initiated with AIBN/CuCla/bpy at 130
0
0
0.068 0.10 0.18 0.09 0.060
0.135 0.20 0.36 0.18 0.12
1.5 21
41.5 70 110 119
“ Detected by GC using THF lated based on eq 1.c Bimodal.
The transition-metal-catalyzed atom transfer radical addition, ATRA, paves a unique and efficient way for carbon—carbon bond formation in organic synthesis.1 Recently, we have successfully introduced this method into polymer chemistry as a novel “living”/controlled radical polymerization process, i.e., atom transfer radical polymerization, ATRP.2’3 Using a simple alkyl halide, R-X, as an initiator and a transition-metal species complexed with suitable ligand(s), Mtn/Lx, as a catalyst, ATRP of alkenes proceeds with a negligible amount of irreversible termination and transfer reactions, leading to polymers with predetermined molecular weight up to Mn ~105 and narrow molecular weight distribution, Mw/Mn down to ~1.10 3 Compared with other “living”/controlled radical polymerization systems reported,4 ATRP works well with a broader class of monomers and offers a more general and efficient way toward various tailor-made polymers.2,3 In this communication, we report that in addition to a typical ATRP initiating system (R-X/Mt/VL*, bulk radical polymerization of vinyl monomers, such as styrene, St, and methyl acrylate, MA, at 100 ± 30 °C), a “living7controlled process is observed using a conventional radical initiator, AIBN, and a transition-metal compound at higher oxidation state, e.g., CunCl2, complexed with suitable ligand(s), e.g., 2.2,-bipyridine, bpy, as a catalyst. Table 1 reports the characterization data of St bulk polymerization at 130 °C initiated by AIBN combined with or without CunCl2 complexed by bpy. The molar ratio of CunCl2 versus AIBN represents a critical parameter for the controlled polymerization while keeping constant [bpy]o/[CunCl2]o of 2/1. In the absence of CunCl2, the polymerization is an ill-controlled process, as evidenced by a much higher molecular weight than expected and broader molecular weight distribution,5 3.0. However, the polymerization becomes Afw/Afn much better controlled when only 2 molar equiv of Cu11CI2 versus initiator is added. The initiator efficiency, f,6 was increased from 22 to 65% and Mw/Mn reduced from 3.0 to 1.8. An increase in [CunCl2]
