1412 Macromolecules, Vol. 43, No. 3, 2010
Kassi and Patrickios
acid, was kindly provided by our colleague Professor A. B. Lowe
of the University of Southern Mississippi (now at the University
of New South Wales, in Sydney, Australia).
characterized using 1H NMR and 13C NMR spectroscopies. 1H
NMR (CDCl3, δ): 1.75 ppm (1sþ1d, CH3CHdCCH3, 6 H), 1.89
ppm (s, CH2dCCH3, 3 H), 4.33 ppm (m, OCH2CH2O, 4 H),
5.53 ppm (s, olefinic methacrylate H trans to CO2, 1 H), 6.07
ppm (s, olefinic methacrylate H cis to CO2, 1 H), and 6.8 ppm
(m, olefinic tiglate H cis to CO2, 1 H). 13C NMR (CDCl3, δ):
11.91 ppm (s, CH3CHdCCH3, 1 C), 14.32 ppm (s, CH3CHd
CCH3, 1 C), 18.19 ppm (s, CH2dCCH3, 1 C), 62.03 and 62.20
ppm (2s, OCH2CH2O, 2 C), 125.88 ppm (s, CH2dCCH3, 1 C),
128.19 ppm (s, CH3CHdCCH3, 1 C), 135.94 ppm (s, CH2d
CCH3, 1 C), 137.78 ppm (s, CH3CHdCCH3, 1 C), and 167.07
and 167.70 ppm (2s, CO2, 2 C).
THF was dried by being refluxed over a potassium-sodium
alloy for three days and was freshly distilled prior to use.
Benzene and N,N-dimethylformamide were distilled from
CaH2. Tetrabutylammonium bibenzoate (TBABB, GTP cata-
lyst) was synthesized by the reaction of tetrabutylammonium
hydroxide and benzoic acid in water, following the procedure of
Dicker et al.,11 and was kept under vacuum until use. DMAE-
MA, MMA, and EGDMA were passed through basic alumina
columns to remove the polymerization inhibitors and any other
acidic impurities. These reagents as well as MT and MAET were
subsequently stirred over CaH2 (to remove the last traces of
moisture and protic impurities) in the presence of added DPPH
free-radical inhibitor and stored in the refrigerator at about
5 °C. Finally, they were freshly distilled under vacuum just
before their use and kept under a dry nitrogen atmosphere. The
GTP initiators were distilled once prior to the polymerization,
but they were neither contacted with CaH2 nor passed through
basic alumina columns because of the risk of hydrolysis. All
glassware were dried overnight at 120 °C and assembled hot
under dynamic vacuum prior to use.
Synthesis of 1-Methoxy-1-trimethylsiloxy-2-methyl Butene
(methyl-MTS, Modified GTP Initiator). Absolute THF (35 mL)
and diisopropylamine (5.88 mL, 4.25 g, 42 mmol) were trans-
ferred into a three-necked 250-mL round-bottom flask contain-
ing a stirring bar and fitted with a rubber septum and a
thermometer and kept under an inert nitrogen atmosphere.
After cooling to 0 °C by placing the flask in an ice-bath,
n-butyllithium (22 mL, 1.9 M, 42 mmol) was added dropwise
using a glass syringe, and the reaction was stirred for 1.5 h at
0 °C. Then, the reaction mixture was cooled down to -78 °C,
and methyl 2-methylbutyrate (5 mL, 4.42 g, 38 mmol) was added
dropwise. The reaction mixture was stirred for 2 h, and tri-
methylsilyl chloride (7 mL, 6.2 g, 57 mmol) was added. After
stirring for 2 h, the formed lithium chloride crystals were filtered
away from the mixture, and the solvent was evaporated off to
give the oily product in 51% yield. The product was further
purified by distillation and characterized by 1H and 13C NMR.
1H NMR (CDCl3, δ): 0.156 ppm (s, Si(CH3)3, 9 H), 0.873 ppm
(t, CCH2CH3, 3 H), 1.53 ppm (d, CdCCH3, 3 H), 1.91 ppm (m,
CCH2CH3, 2 H), and 3.48 ppm (s, OCH3, 3 H). 13C NMR
(CDCl3, δ): 0.1 ppm (s, Si(CH3)3, 3 C), 12.43 ppm (s, CCH2CH3,
1 C), 14.05 ppm (s, CdCCH3, 1 C), 23.44 ppm (s, CCH2CH3, 1 C),
56.55 ppm (s, OCH3, 1 C), 96.76 ppm (s, -CdC(OCH3)OSi(CH3)3,
1 C)) and at 149.16 ppm (s, -CdC(OCH3)OSi(CH3)3, 1 C).
Polymerizations. GTP. A catalytic amount of TBABB (∼20
mg, ∼40 μmol, ∼3% mol relative to the initiator) was trans-
ferred to a 100-mL round-bottom flask containing a stirring bar.
The flask was immediately sealed with a rubber septum, and it
was purged with dry nitrogen. Freshly distilled THF was sub-
sequently transferred directly into the flask via a glass syringe,
followed by the addition of the MTS initiator (0.3 mL, 0.258 g,
1.48 mmol). Finally, the monomers MAET, MT, MMA,
DMAEMA, and EGDMA were added in the appropriate order.
The reactions were carried out at 20 °C, and the polymerization
exotherm was monitored by a digital thermometer to follow the
progress of the polymerization reaction. A similar procedure
was followed for the polymerizations using the methyl-MTS
initiator.
ATRP. CuBr (48.4 mg, 0.347 mmol), CuBr2 (2.7 mg, 0.012
mmol), 2,20-bipyridine (0.109 mg, 0.7 mmol), MT (1.5 mL, 1.37 g,
12 mmol), and 3.17 mL of DMF were added to a Schlenk flask
containing a stirring bar and kept under an inert nitrogen
atmosphere. The mixture was degassed via three freeze-
pump-thaw cycles. Ethyl 2-bromoisobutyrate (35.3 μL, 46.9
mg, 0.241 mmol) was subsequently introduced, and the reaction
flask was placed in an oil bath thermostatted at 70 °C for 21 h.
RAFT Polymerization. A solution of MT (1 mL, 0.913 g,
8 mmol), 2-(2-carboxyethylsulfanylthiocarbonylsulfanyl)propionic
acid RAFT CTA (0.042 g, 0.164 mmol), and 2,20-azobis-
isobutyronitrile (0.02 g, 0.102 mmol) in benzene (2 mL) were
transferred to a 100-mL round-bottom flask containing a
magnetic stirring bar. The system was degassed by three freeze-
pump-thaw cycles and was subsequently placed in an oil bath at
65 °C for 24 h.
Monomer Synthesis. Methyl Tiglate (MT). Tiglic acid (7.0 g,
0.070 mol), methanol (200 mL, 182 g, 5.70 mol), and sulfuric
acid catalyst (1 mL) were transferred to a 250-mL round-bottom
flask fitted with a condenser. The mixture was stirred at 65 °C
for 2 days. Subsequently, the mixture was diluted with 200 mL of
diethyl ether, washed three times with 150 mL of 5% NaHCO3,
three times with 150 mL water, and finally with 50 mL of a
saturated NaCl aqueous solution. The organic layer was dried
with anhydrous MgSO4, and the solvent was evaporated off
under reduced pressure to give 3.97 g (0.035 mol) of pure methyl
tiglate in 49.7% yield. This was characterized using 1H and 13
C
NMR spectroscopies. 1H NMR (CDCl3, δ): 1.75 ppm (1sþ1d,
CH3CHdCCH3, 6 H), 3.68 ppm (s, OCH3, 3 H), and 6.8 ppm
(m, CH3CHdCCH3, 1 H cis to CO2CH3). 13C NMR (CDCl3, δ):
11.79 ppm (s, CH3CHdCCH3, 1 C), 14.07 ppm (s, H3CCHd
CH3, 1 C), 51.39 ppm (s, -OCH3, 1 C), 128.32 ppm (s, H3CCHd
CCH3, 1 C), 136.96 ppm (s, H3CCHdCCH3, 1 C), and 168.37
ppm (s, -COOCH3, 1 C).
2-Hydroxyethyl Tiglate. Tiglic acid (10 g, 0.1 mol), ethylene
glycol (28 mL, 0.5 mol), and sulfuric acid catalyst (1 mL) were
transferred to a 100-mL round-bottom flask with a condenser.
The mixture was stirred at 65 °C for 17 h. After evaporation of
ethylene glycol, the product was purified by column chromato-
graphy (silica gel/hexane/ethyl acetate = 50:50 v/v) at a final
yield of 59%. The purity of 2-hydroxyethyl tiglate was con-
firmed using 1H and 13C NMR spectroscopies. 1H NMR
(CDCl3, δ): 1.75 ppm (1sþ1d, CH3CHdCCH3, 6 H), 3.84
ppm (t, OCH2CH2OH, 2 H), 4.26 ppm (t, OCH2CH2OH,
2 H), and 6.8 ppm (m, CH3CHdCCH3, 1 H cis to CO2). 13C
NMR (CDCl3, δ): 11.79 ppm (s, CH3CHdCCH3, 1 C), 14.18
ppm (s, CH3CHdCCH3, 1 C), 60.81 ppm (s, OCH2CH2OH, 1
C), 65.90 ppm (s, OCH2CH2OH, 1 C), 128.08 ppm (s, CH3CHd
CCH3, 1 C), 137.86 ppm (s, CH3CHdCCH3, 1 C) and at 168.35
ppm (s, -CO2, 1 C).
2-(Methacryloyloxy)ethyl Tiglate (MAET). 2-Hydroxyethyl
tiglate (8.45 g, 0.059 mol), Et3N (41.0 mL, 29.3 g, 0.29 mol), and
absolute THF (100 mL) were transferred to a 100-mL round-
bottom flask containing a magnetic stirring bar. The solution
was stirred and cooled down to 0 °C. After stabilization of the
temperature, methacryloyl chloride (7.35 mL, 7.94 g, 0.076 mol)
was added dropwise using a glass syringe, and the reaction was
stirred for 1 h at room temperature. Subsequently, the mixture
was filtered and passed through a basic alumina column to
remove the acidic impurities. Then, the solvent was evaporated
off to give pure monomer in 76% yield. Finally, MAET was
stirred over CaH2 in the presence of DPPH to remove all of the
moisture and the last traces of acidic impurities. MAET was
Polymer Oxidation. Linear homopolymer MAET20 (0.5 g,
2.36 meq of MAET monomer repeating units), carbon tetra-
chloride (70 mL, 111 g, 0.7 mol), and meso-tetraphenylporphyrin
(30 mg, 48 μmol) as sensitizer were transferred to a 100-mL