Synthesis of Polybenzamide-b-Polystyrene Block Copolymer via Combination of
Chain-growth Condensation Polymerization (CGCP) and Atom Transfer Radical
Polymerization (ATRP)
Chih-Feng Huang, Akihiro Yokoyama, and Tsutomu Yokozawa *
Department of Material and Life Chemistry, Kanagawa University, Rokkakubashi, Kanagawa-ku,
Yokohama 221-8686, Japan
Materials
Imidazole (99%), octanal (98%), acetic acid (95%), sodium triacetoxyborohydride (98%), anisole (99%), N,N,N',N",N" -pentamethyldiethylenetriamine (PMDETA, 99%), 2,2′-bipyridyl
(Bpy, 99%), 1.0 M lithium hexamethyldisilazide/tetrahydrofuran (1.0 M LiHMDS/THF solution), 1.0 M tetrabutylammonium fluoride/tetrahydrofuran (1.0 M TBAF/THF solution), and trifluoroacetic acid (TFA) were purchased from Aldrich and were used without further purification. Lithium chloride (LiCl, 98%), naphthalene (99%), methyl 4-
(hydroxymethyl)benzoate (98%), tert -butylchlorodimethylsilane (98%), 2-bromoisobutyryl bromide (99%), and ethyl 4-aminobenzoate (97%) were purchased from TCI and were used without further purification. Copper bromide (CuBr, 98%, Acros) was washed with glacial acetic acid in order to remove any soluble oxidized species, filtered, washed with ethanol and dried under vacuum. Tris(2-dimethylaminoethyl)amine (Me
6
TREN), and tris[(2-pyridyl)methyl]amine
(TPMA) were synthesized according to the literature.
1
Monomers 3
2
and 5
3 were synthesized according to our previous reports. Triethylamine, styrene, and solvents were purified by distillation prior to use.
Synthesis of Initiator 1
A 200-mL one-neck round-bottomed flask was dried and refilled with N
2
. Methyl 4-
(hydroxymethyl)benzoate (4.15 g, 25 mmol) and triethylamine (4.20 mL, 30 mmol) were mixed in dry CH
2
Cl
2
(60 mL) with stirring for 15 min. A solution of 2-bromoisobutyryl bromide (3.70 mL, 30 mmol) in dry CH
2
Cl
2
(20 mL) and was added dropwise to the mixture, with stirring at 0
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°C. Stirring was continued at room temperature for 16 h under N
2
; then the reaction mixture was quenched with water and extracted with CH
2
Cl
2
. The organic layer was washed with saturated
NaHCO
3
and water, and dried over MgSO
4
. After filtration and evaporation of the solvents, the crude product was purified on a basic alumina column (ethyl acetate/hexane = 1/4 (v/v)) to give a light-yellowish liquid (6.46 g, yield 82%).
1
H NMR (600 MHz, CDCl
3
,
δ
, ppm): 8.06 (m, 2H), 7.46 (m, 2H), 5.26 (s, 2H), 3.92 (s, 3H),
1.97 (s, 6H).
Synthesis of Initiator 2
A 250-mL round-bottomed flask was charged with tert -butylchlorodimethylsilane (5.42 g, 36 mmol), imidazole (2.45 g, 36 mmol), and dry THF (50 mL). Methyl 4-(hydroxymethyl)benzoate
(4.99 g, 30 mmol) in dry THF (20 mL) was gradually added to the mixture via an additional funnel, with stirring at room temperature. The reaction mixture was stirred for another 22 h at room temperature. Water was added to terminate the reaction and the mixture was extracted with
CH
2
Cl
2
. The combined organic layer was washed with saturated NaHCO
3
and water; then dried over MgSO
4
. After filtration and evaporation of solvents, the crude product was purified by silica gel column chromatography with hexane as the first eluent, followed by CH
2
Cl
2
. A colorless liquid was obtained (7.54 g, yield 75%).
1
H NMR (600 MHz, CDCl
3
,
δ
, ppm): 8.02-7.98 (m, 2H), 7.40-7.36 (m, 2H), 4.78 (s, 2H), 3.89
(s, 3H), 0.94 (s, 9H), 0.10 (s, 6H);
13
C NMR (150 MHz, DMSOd
6
,
δ
, ppm): 165.92, 146.64,
128.97, 128.08, 125.72, 63.67, 51.81, 25.60, 17.82, -5.54.
Synthesis of Polybenzamide-Br (PBzAm-Br) Macroinitiator through Two Steps (para-type as an example):
(1) Deprotection
PpBzAm-OTBS (0.51 g, 0.17 mmol) was dissolved in dry THF (3 mL). 1.0 M TBAF/THF solution (0.20 mL, 0.20 mmol) was added at room temperature under Ar. The mixture was kept at room temperature for 2 h.
1
H NMR analysis demonstrated that the reaction was quantitative.
The reaction mixture was quenched with water; then extracted with CH
2
Cl
2
. The organic layer was washed with water and dried over anhydrous MgSO
4
. Yellowish viscous poly( para benzamide)-OH (i.e., PpBzAm-OH) was obtained (0.48 g, yield 94%).
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(2) Acylation
A 50 mL one-neck round-bottomed flask was dried and refilled with N
2
. PpBzAm-OH polymer (0.48 g, 0.16 mmol) and triethylamine (0.22 mL, 1.6 mmol) were mixed with dry
CH
2
Cl
2
(10 mL) with stirring for 15 min. A solution of 2-bromoisobutyryl bromide (0.20 mL,
1.6 mmol) in dry CH
2
Cl
2
(5 mL) was added dropwise to the mixture with stirring at 0 °C, and stirring was continued at room temperature for 23 h under N
2
.
1
H NMR analysis demonstrated that the reaction was quantitative. The reaction mixture was quenched with water, then extracted with CH
2
Cl
2
. The organic layer was washed with saturated NaHCO
3
and water, and the solvent was removed. The crude product was dissolved in CH
2
Cl
2
and twice precipitated into methanol/water = 9/1 (v/v) to give a yellowish viscous oil. Poly( para -benzamide) with the
ATRP initiating site (i.e., PpBzAm-Br) was obtained (0.40 g, yield 83%).
Deprotection of PSt-b-PmOOBBzAm Block Copolymer
A 10 mL-flask, equipped with a three-way stopcock, was dried, purged with argon and then charged with PStb -P(mOOBBzAm) (32 mg) and dry CH
2
Cl
2
(1.5 mL). TFA (1 mL) was added and the mixture was stirred at room temperature for 1 day under argon for removal of the OOB side group. The solvent was pumped out. The crude product was dissolved in CH
2
Cl
2
and twice precipitated into hexane to afford poly( N -Hmeta -benzamide)b -polystyrene (PmNHBzAmb -
PSt) block copolymer as a white powder (22 mg, yield 78%).
REFERENCES
1. (a) Queffelec, J.; Gaynor, S. G.; Matyjaszewski, K. Macromolecules 2000, 33, 8629-8639; (b)
Tyeklar, Z.; Jacobson, R. R.; Wei, N.; Murthy, N. N.; Zubieta, J.; Karlin, K. D. J. Am. Chem.
Soc. 1993, 115, 2677-2689.
2. Yokozawa, T.; Muroya, D.; Sugi, R.; Yokoyama, A. Macromol. Rapid Commun. 2005, 26,
979-981.
3. Ohishi, T.; Sugi, R.; Yokoyama, A.; Yokozawa, T. J. Polym. Sci., Part A: Polym. Chem. 2006,
44, 4990-5003.
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FIGURE S1 GPC traces (eluent: THF) for CGCP of the methyl ester monomer 3 via initiators 1 and 2 (M/I/LiHMDS = 10/1/10 at -10 °C in THF with [M]
0
= 0.3 M).
FIGURE S2 FT-IR spectra before and after treatment of block copolymer with TFA: (a) PStb -
PmOOBBzAm, treatment for (b) 1 day and (c) 4 days.
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