Supporting Information
© Wiley-VCH 2008
69451 Weinheim, Germany
Phosphorus Containing Ligands for Iron(III)-Catalyzed
Atom-Transfer Radical Polymerization
Zhigang Xue,† Nguyen Thuy Ba Linh,† Seok Kyun Noh,*,† and Won Seok Lyoo‡
School of Display and Chemical Engineering, Yeungnam University, 214-1 Dae-dong, Gyeongsan,
Gyeongbuk, 712-749, Republic of Korea, and School of Textiles, Yeungnam University, 214-1
Dae-dong, Gyeongsan, Gyeongbuk, 712-749, Republic of Korea.
*
Corresponding author. E-mail: [email protected].
†
School of Display and Chemical Engineering, Yeungnam University.
‡
School of Textiles, Yeungnam University.
Experimental Section
2-[(Diphenylphosphino)methyl]pyridine (DPPMP) was synthesized using the method described by our
published paper.[1]
Synthesis of N-(2-diphenylphosphinobenzylidene)aniline (DPPBA). The ligand was prepared via a
Schiff base reaction[2] carried out under a nitrogen atmosphere. DPPB (0.512 g, 1.76 mmol) and aniline
(0.166g, 1.78mmol) in toluene (15 ml) was stirred at a reflux temperature for 24 h. The mixture was
concentrated under a reduced pressure, and the residue was treated with hexane (20 ml). Filtration of
insoluble material gave yellow solution. The pure ligand was obtained upon recrystallization from the
solution. Yield: 0.526 g, 84%. 1H NMR (CDCl3, ppm): 10.51 (d, 1H –CH=N), 8.47 (m, 1H, ArH), 7.43 (t,
2H, ArH), 7.35-6.85 (m, 16H, ArH).
Polymerization Experiments
Normal ATRP of MMA. The polymerization reaction was carried out using the following procedure: a
Schlenk flask was charged with FeBr2 (100.8 mg, 0.467 mmol) and the DPPP ligand (246.2 mg, 0.934
mmol). The flask was sealed with a rubber septum and was cycled three times between vacuum and
nitrogen to remove the oxygen. The degassed solvent (in solution polymerization) and MMA (5 mL, 46.7
mmol) were then added to the flask through degassed syringes. The solution was stirred for 20 min at
room temperature and then the desired amount of initiator, EBriB (69.3 μL, 0.234 mmol), was added. The
flask was sealed with a new rubber septum and degassed by three freeze-pump-thaw cycles to remove the
oxygen. The flask was immersed in a thermostated oil bath. At timed intervals, samples were withdrawn
from the flask with a degassed syringe and diluted with THF and then filtered through a column filled
with neutral aluminum oxide to remove the iron catalyst. Parts of the polymer solution were used for gas
chromatography (GC) measurements in order to determine the monomer conversions. Other parts of the
PMMA solution were then precipitated using an excess of n-hexane, and these polymers were dried under
vacuum for 24 h in preparation for gel permeation chromatography (GPC) measurements to determine the
molecular weights of the polymers.
Iron(III)-catalyzed ATRP of MMA. The polymerization reaction was carried out using the following
procedure: a Schlenk flask was charged with FeBr3 (138.2 mg, 0.467 mmol) and the DPPP ligand (246.2
mg, 0.934 mmol). The flask was sealed with a rubber septum and was cycled three times between vacuum
and nitrogen to remove the oxygen. The degassed solvent (4 mL) (in solution polymerization), anisole (1
mL) and MMA (5 mL, 46.7 mmol) were then added to the flask through degassed syringes. The solution
was stirred for 20 min at room temperature and then the desired amount of EBriB (69.3 μL, 0.467 mmol)
was added. The flask was sealed with a new rubber septum and degassed by three freeze-pump-thaw
cycles to remove the oxygen. The flask was immersed in a thermostated oil bath. At timed intervals,
samples were withdrawn from the flask with a degassed syringe and diluted with THF and then filtered
through a column filled with neutral aluminum oxide to remove the iron catalyst.
Characterizations. 1H (300MHz) NMR spectra was obtained on a Bruker DPX-300 FT-NMR
spectrometer in CDCl3 solvent. The monomer conversion was determined in THF solvent with anisole as
an internal standard with a HP 6890 gas chromatography equipped with a FID detector and a J&W
Scientific 30 m DB WAX Megabore column. The injector and detector temperatures were kept at 250℃.
The analysis was run isothermally at 40℃ for 1 min, following which the temperature was increased to
120℃ at a heating rate of 20℃/min and held at this temperature for 1 min, before being increased again
to 180℃ at a heating rate of 10℃/min and being held at this temperature for 1 min. The number-average
molecular weight and molecular weight distribution (Mw/Mn) of the polymers were determined by GPC
using Waters columns (Styragel, HR 5E) equipped with a Waters 515 pump and a Waters. THF was used
as the eluent at a flow rate of 1 mL/min. Linear PS standards (1.31 × 103 g/mol ~ 3.58 × 106 g/mol) were
used for calibration.
Table 1S. Fe-catalyzed ATRPs of MMA with Phosphorus Containing Ligands[a]
Entry
1
2
3
4
5
6
7
8
9
10
11
Ligand
TPP
DPPP
DPPMP
DPPB
DPPBA
DPPDMA
12
13
DPPDMX
14
Conv.
[%]
72
76
73
Mn,theo[b]
Mn,GPC
PDI
FeBr3
FeBr2
FeBr3
Time
[h]
1
1
4
7400
7800
7500
9500
7900
8400
1.24
1.48
1.18
FeBr2
FeBr3
FeBr2
FeBr3
4
6
6
3
85
84
90
75
8750
8600
9200
7700
9200
8800
12100
6400
1.30
1.16
1.50
1.17
FeBr2
FeBr3
FeBr2
FeBr3
3
3
2.5
4
83
78
80
82
8450
8000
8250
8400
8800
10900
9600
8100
1.37
1.30
1.50
1.19
FeBr2
4
86
8800
9300
1.31
FeBr3
20
83
8500
9200
1.20
FeBr2
20
89
9100
12300
1.59
Metal salt
[a] Reactions were performed in toluene at 80 ℃, [MMA]0 = 4.67 M, [MMA]0:[Fe]0:[ligand]0:[EBriB]0
= 100:1:2:1. [b] Mn,theo = ([MMA]0/[EBriB]0)MMMA × Conv.(%) + MEBriB; MMMA and MEBriB are the
molecular weights of the monomer, MMA and the initiator, EBriB.
Comments on Table 1S: The Iron(III)-catalyzed ATRPs of MMA with phosphorus ligands can be
controlled very well.
Mechanistic Investigations: As shown in this article, a remarkable ATRP of MMA was observed using
only iron(III)/DPPP in the absence of any free radical initiator or reducing agent. An addition reaction of
CuBr2 and MMA which resulted in a reduction of Cu(II) to Cu(I) was reported by Matyjaszewski et al.[3]
In this reaction, MMA reduced the higher oxidation state metal to lower one, and the mechanism of
polymerization can be explained as a normal ATRP. As a result, the polymerization of MMA was
controlled well due to the occurrence of FeBr2/FeBr3/DPPP catalyst system. Firstly, the polymerization of
MMA was carried out using FeBr3/DPPP as complex without initiator in toluene at 80 ℃. The reaction
was so slow that conversion reached 36% after 30 h. Importantly, the polymers were obtained from this
reaction, which indicated that the polymerization could be initiated by one initiator and iron(II) obtained
from the addition reaction.
100
No Addition
90
Radical Scavenger
Addition
Conversion (%)
80
Mn
PDI
(b)
(b)
18500
1.18
(a)
5100
1.12
Galvinoxyl
(c)
5200
1.13
(d)
5100
1.11
20
22
70
60
O
50
C
H
O
40
Galvinoxyl
30
(c)
(a)
20
(d)
10
TEMPO
TEMPO
O N
0
0
1
2
3
4
5
6
Time (h)
7
8
9
10
16
18
Elution Time (min)
Figure 1S. Plot of the monomer conversion against time and GPC curves of the PMMAs for the ATRP of
MMA in toluene at 80 ℃ by the addition of radical scavenger. [MMA]0 = 4.67 M;
[MMA]0/[EBriB]0/[FeBr3]0/[DPPP]0/[Radical scavenger]0= 200:1:1:2:10.
In addition, to understand the mechanism of polymerization of MMA initiated by FeBr3/DPPP/EBriB,
a radical scavenger (TEMPO or galvinoxyl) was added to the reaction system after 1 h (conversion =
22%). Figure 1S shows the plot of the monomer conversion against time and GPC curves of the PMMAs.
After 9 h, the molecular weights were not changed and molecular weight distributions maintained narrow,
which indicated that the polymerization was immediately terminated by the radical scavengers. Therefore,
the Fe(III)-catalyzed polymerization of MMA proceeded a radical mechanism.
TEMPO
Figure 2S. 1H NMR spectrum (solvent, CDCl3) of the polymers obtained before and after the addition of
TEMPO in toluene at 80 ℃. [MMA]0 = 4.67 M; [MMA]0/[EBriB]0/[FeBr3]0/[DPPP]0/[TEMPO]0=
200:1:1:2:10.
Figure 2S shows the 1H NMR spectrum of the polymers obtained before and after the addition of
TEMPO. Two new peeks at 5.5 and 6.2 ppm were appeared after the addition, which were characteristic
of olefinic methylene protons obtained from the reaction between TEMPO and growing radical.[4]
5
DPPP
FeBr2
Absorbance
4
FeBr3
FeBr2(DPPP)
3
FeBr2(DPPP)2
FeBr3(DPPP)
FeBr3(DPPP)2
2
1
0
300
400
500
600
700
Wavelength (nm)
Figure 3S. UV-vis spectra of iron catalysts
Comments on Figure 3S: The formation of FeBr3/DPPP was confirmed by UV-vis measurements.
End-group Analysis of PMMA-Br. The end-group analysis of ATRP polymers is important, because
polymer chains with halogen end groups act as a macroinitiator. It can be reactivated in the presence of
the ATRP catalyst system so as to initiate the polymerization of the second monomer to form block, graft
or star polymers, depending on the position and number of initiation sites.
PMMA-b-PMMA
Mn,GPC = 102,000
Mw/Mn = 1.12
Mn,GPC = 136,200
Mw/Mn = 1.12
PMMA-Br
Mn,GPC = 18,500
Mw/Mn = 1.18
12
14
16
18
20
22
Elution Time (min)
Figure 4S. GPC traces of the macroinitiator (PMMA-Br) and its chain extended polymers (PMMA-bPMMA) obtained at 16 and 24 h, respectively.
The chain extension experiment of MMA with PMMA-Br (Mn,GPC = 18500, Mw/Mn = 1.18) as
macroinitiator to initiate the polymerization of fresh MMA was carried out in toluene (50%, v/v) at 80 ℃
using
FeBr3/DPPP
as
the
catalyst.
The
experiment
was
conducted
using
a
ratio
of
[MMA]0/[macroinitiator]0/[FeBr3]0/[DPPP]0 = 200:0.01:1:2. Figure 4S shows the GPC trace of the
PMMA macroinitiator and the PMMA-b-PMMA copolymers. After the chain extension reaction, the
Mn,GPC of PMMA increased and the polydispersities of the final polymers kept quite narrow. These results
clearly establish that the PMMA obtained by ATRP with FeBr3/DPPP catalyst system is living polymer.
References and Notes
[1] Z. Xue, B. W. Lee, S. K. Noh, W. S. Lyoo, Polymer 2007, 48, 4704.
[2] E. Shirakawa, Y. Nakao, Y. Murota, T. Hiyama, J. Organomet. Chem. 2003, 670, 132.
[3] A. K. Nanda, S. C. Hong, K. Matyjaszewski, Macromol. Chem. Phys. 2003, 204, 1151.
[4] T. Nishikawa, T. Ando, M. Kamigaito, M. Sawamoto, Macromolecules 1997, 30, 2244.