Communications
times faster than that in SBRP, TERP, and IRP. The result
Keywords: bismuth · polymerization · radical reactions ·
reaction mechanisms
.
indicates that organobismuthines are also the best radical
initiators among the heteroatom compounds. Azo initiators
cause the formation of the corresponding radical-initiated
polymer upon its consumption and increase the formation of
“dead” polymers. Therefore, the controllability of the poly-
merization decreases in the presence of azo initiators. In this
respect, efficient thermal generation contributed considera-
bly to the precise control in styrene and MMA polymeri-
zations.
In summary, we have demonstrated that organobismu-
thines are excellent initiators and mediators for the highly
controlled living radical polymerization. The results clearly
open the possibility of the use of organobismuthines in
controlled radical reactions. Furthermore, the excellent con-
trollability and versatility of BIRP would be highly attractive
for the synthesis of a variety of functional nanomaterials.[16]
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Experimental Section
1a: Lithium diisopropylamide (14.0 mL, 2.0m in heptane, THF, and
ethylbenzene, 28 mmol) was slowly added to a solution of methyl
isobutyrate (2.86 g, 28 mmol) in THF (25 mL) at À788C. The
resulting mixture was stirred for 10 min at this temperature, and
was slowly warmed to À308C over 1 h. Dimethylbismuthanyl
bromide[15] (8.9 g) in THF (25 mL) was added to the reaction mixture,
and the solution was slowly warmed to 08C over 1 h. The precipitate
was filtered off by passing the mixture through glass wool under a
nitrogen atmosphere, and the filtrate was evaporated under reduced
pressure and then distilled under reduced pressure (b.p. 328C/
1.5 mmHg) to give 1a as an slightly yellow oil (4.45 g, 47%). This
compound is sensitive to oxygen, but can be stored for a long period
1
under an inert atmosphere. H NMR (400 MHz, CDCl3): d = 1.08 (s,
6H, Bi(CH3)2), 1.77 (s, 6H, C(CH3)2), 3.72 ppm (s, 3H, OCH3);
13C NMR (100 MHz, CDCl3): d = 10.12, 21.84, 24.12, 50.68,
178.28 ppm; HRMS (EI) m/z: Calcd for C7H15O2Bi [M]+ 340.0875;
found 340.0871; IR (neat): n˜ = 815, 1135, 1185, 1270, 1460, 1695,
2940 cmÀ1
.
Typical procedure of polymerization of styrene: A solution of
styrene (1.04 g, 10 mmol) and 1a (41 mL, 0.1 mmol) was heated at
1008C for 4 h with stirring under a nitrogen atmosphere in a glove
box. A small portion of the reaction mixture was taken and dissolved
in CDCl3. The conversion of monomer (96%) was determined by
1H NMR spectroscopy. The rest of reaction mixture was dissolved in
CHCl3 (4 mL) and poured into vigorously stirred methanol (200 mL).
The product was collected by filtration and dried under reduced
pressure at 408C to give 1.01 g of polystyrene. The Mn value (10500)
and PDIvalue (1.07) were determined by size-exclusion chromatog-
raphy calibrated with polystyrene standards.
[12] For the effect of a methyl group on bond dissociation energies,
see C. G. Hawker, Acc. Chem. Res. 1997, 30, 373 and also
reference [9a].
[13] A. Goto, T. Terauchi, T. Fukuda, T. Miyamoto, Macromol. Rapid
Commun. 1997, 18, 673.
[14] T. Fukuda, A. Goto, K. Ohno, Macromol. Rapid Commun. 2000,
21, 151.
[15] A. J. Ashe III, E. G. Ludwig, Jr., J. Oleksyszyn, Organometallics
1983, 2, 1859.
[16] The toxicity of organobismuthines is not clear. Hence, they
should be handled with care.
Received: November 1, 2006
Published online: January 5, 2007
1306
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 1304 –1306