Novel neutral phenylnickel phosphine compounds bearing iminoaryl-substituted cyclopentadienyl ligand: Synthesis, characterization and their styrene polymerization behaviors

Article abstract of DOI:10.1016/j.inoche.2008.01.006

Four neutral phenylnickel phosphine compounds linked iminoaryl-substituted cyclopentadienyl ligand of the type [NiL(PPh₃)Ph] have been synthesized and characterized. All these complexes exhibit high catalytic activity in catalyzing styrene poly

Full text of DOI:10.1016/j.inoche.2008.01.006

Available online at www.sciencedirect.com
Inorganic Chemistry Communications 11 (2008) 487–491
www.elsevier.com/locate/inoche
Novel neutral phenylnickel phosphine compounds bearing
iminoaryl-substituted cyclopentadienyl ligand:
Synthesis, characterization and their styrene polymerization behaviors
a,
a
a
*
Wen-Ping Wei , Xiao-Ling Wang , Dan-Feng Zhang ,
Qiao-Long Yuan a, Bao-Tong Huang a,b
a School of Materials Science & Engineering, East China University of Science and Technology, Shanghai 200237, China
b State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, China
Received 15 December 2007; accepted 7 January 2008
Available online 19 January 2008
Abstract
Four neutral phenylnickel phosphine compounds linked iminoaryl-substituted cyclopentadienyl ligand of the type [NiL(PPh3)Ph]
have been synthesized and characterized. All these complexes exhibit high catalytic activity in catalyzing styrene polymerization under
the action of MAO and afford bimodal polystyrene.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Iminoaryl-substituted cyclopentadienyl ligand; Arylnickel phosphine; X-ray crystal structure; Styrene polymerization
An important class of hemilabile ligands consists of
functionalized cyclopentadienyl ligands represented by
Cp^L, with ^ denoting the side chain linking the Cp ligand
to a functional group L such as NRR0, NR, OR, PRR0, SR,
AsRR0, and C@C [1]. The main role of the Cp moiety is to
anchor these multidentate ligands to metal centers, while
the reversible coordination of L modulates the reactivities
of the metal center [1]. Olefin polymerization catalyzed
by late transition metal catalysts have been received consid-
erable attentions in recent years [2] and neutral arylnickel
phosphine complexes bearing iminoaryl ligand have been
prepared and widely studied since the pioneer work was
reported by Grubbs and co-workers in 1998 [3]. In the past
work, most attentions in this area were focused on the pen-
dant hemilabile moiety of the cyclopentadienyl ligand of
the pre-transition metal complexes [1] and the increasing
steric hindrance on the ligand of the late transition metal
catalysts [2,3]. There were several reports on the synthesis
and styrene polymerization behaviors of the late transition
metal complexes bearing non-substituted cyclopentadienyl
ligands [4] and amine modified cyclopentadienyl ligands
[5]. Styrene polymerization activities of these complexes
were low to moderate in these reports [4,5]. However, there
is still no structure and coordination report about late tran-
sition metal complexes bearing iminoaryl substituted cyclo-
pentadienyl ligand. We report herein our study on the
coordination ability of the iminoaryl substituted cyclopen-
tadienyl ligands with the neutral phenylnickel phosphine
and their styrene polymerization behaviors.
Ligand precursors were prepared by the reaction of
cyclopentadienyl sodium and N-aryl-2,2,2-trifluoroacetimi-
doyl chloride [6] in THF according to the literature [7]. All
attempts to synthesize compound (cyclo-C5H4)C(CF3)
@N(C6H5) failed such as modification of reactants ratio
and temperature of the reaction. The reaction of (cyclo-
C5H4)(C(CF3)@N(C6H5))2, (cyclo-C5H5)C(CF3)@N(2,6-di-
methyl-C6H3), (cyclo-C5H5)C(CF3)@N(2,6-diethyl-C6H3),
*
Corresponding author.
E-mail address: wenpingwei@yahoo.com.cn (W.-P. Wei).
1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2008.01.006

488
W.-P. Wei et al. / Inorganic Chemistry Communications 11 (2008) 487–491
(cyclo-C5H5)C(CF3)@N(2,6-diiso-propyl-C6H3) with NaH
in THF leaded the formulation of sodium derivatives,
which without further purification reacted with trans-
Ni(PPh3)2PhCl to yield the compounds Ni(PPh3)PhL
(where L = (g5-cyclo-C5H3)(C(CF3)@N(C6H5))2 (L1), 1;
(g5-cyclo-C5H4)C(CF3)@N(2,6-dimethyl-C6H3) (L2), 2;
(g5-cyclo-C5H4)C(CF3)@N(2,6-diethyl-C6H3) (L3), 3; (g5-
cyclo-C5H4)C(CF3)=N(2,6-diiso-propyl-C6H3) (L4), 4) [2]
CF3
N
N
N
Ni
F3C
PPh3
NaH
trans-Ni(PPh3)2(Ph)Cl
2
CF3
R
1
CF3
R
N
trans-Ni(PPh3)2(Ph)Cl
NaH
Ni
F3C
N
Ph3P
R'
R'
2 R=R'=CH3
3 R=R'=CH2CH3
4 R=R'=CH(CH3)2
Scheme 1. Synthesis of complexes 1–4.
˚
Fig. 1. X-ray crystal structure determination of 1 selected bond length (A) and angles (°): Ni–C(1), 2.136(4); Ni–C(2), 2.147(4); Ni–C(3), 2.225(4); Ni–
C(4), 2.120(4); Ni–C(5), 2.165(4); Ni–P(1), 2.1451(14); Ni–C(22), 1.908(4); N(1)–C(6), 1.265(5); N(1)–C(7), 1.412(6); C(3)–C(14), 1.469(6); C(5)–C(6),
1.479(6); C(6)–C(13), 1.531(6); C(22)–Ni–C(4), 98.38(18); C(22)–Ni–C(1), 145.64(18); C(22)–Ni–P(1), 90.07(14); C(6)–N(1)–C(7), 120.9(4); C(14)–N(2)–
C(15), 121.7(4); C(5)–C(6)–C(13), 115.8(4); C(3)–C(14)–C(21), 117.3(5); P(1)–Ni–C(2), 105.17(13); and C(22)–Ni–C(5), 109.48(18).

W.-P. Wei et al. / Inorganic Chemistry Communications 11 (2008) 487–491
489
as shown in Scheme 1. All complexes were characterized by
elemental analysis, H NMR, infrared spectra and mass
spectrum [8].
iminophenyl group. In the complex 1, the diiminophenyl
moieties in the ligand stand at the two sides of the plane
Ni–P–Ph. The iminophenyl group in 4 is also same to that
in 1 with a little difference. Because of steric hindrance of
PPh3 and Ph, the diiminophenyl moieties are un-symmetri-
cal in the dimensional structure in the molecular structure
of 1. And Ni–P(1) bond in 1 is a little longer than that in 4
due to the steric influence of the two iminophenyl moieties
on the cyclopentadienyl group in 1. In the crystal struc-
1
Elemental analysis of the complexes agrees with the cal-
culated value. The mass spectra result confirms the molecu-
lar weight of complex. In the IR spectra, the absorption of
C@N in the ligand around 1600 cmꢀ1 changes little. This
clearly shows that the iminoaryl group in the ligand is un-
coordinated in all the compounds and therefore the ligand
bonds through the cyclopentadienyl group to the central
metal. The absorption around 1440 cmꢀ1 and 700 cmꢀ1 is
the characteristic peak of mC–P and mNi–P [9], which accounts
for the coordination of nickel atom and P atom in the com-
plex. The signals shown in the 1H NMR spectra of the H on
the cyclopentadienyl cycle around 5.0 ppm split into two
groups due to influence of the iminoaryl substitution.
The ORTEP diagram of 1 and 4 are shown in Figs. 1
and 2, respectively, along with selected bond lengths and
angles [10].
˚
tures, Ni–P(1) bond length is 2.1451 A (in 1) and
˚
2.1358 (A) (in 4). Compared with Ni–P length in other
arylnickel phosphine complexes reported (the Ni–P bond
˚
˚
range is from 2.148 A to 2.1868 A) [3,5,11], the bond of
Ni–P in these complexes is shorter. In addition to the
affection of N-aryl-2,2,2-trifluoroacetimidoyl group, the
g5Cp–Ni bond is much stronger, which makes the nickel
atom more electron deficient. Inversely, this makes the
Ni–P(1) bond stronger. With the Ni–P(1) bond length
stronger and shorter, the steric hindrance around the nickel
˚
In the molecular structure of the two complexes, nickel
atom coordinates with cyclopentadienyl cycle to form
g5Cp–Ni while five carbon atoms in the cyclopentadienyl
group are almost arranged in a plane. The X-ray results
also show that in the molecule, there is no coordination
between the nickel atom and nitrogen atom in the
atom rises, which makes the bond Ni–C(22) of 1.908(4) A
˚
(in 1) and Ni–C(20) of 1.916(3) A (in 4) much longer.
Because the steric hindrance around nickel atom in 1 which
contains two iminophenyl groups in the cyclopentadienyl
plane is higher than that in 4, the Ni–P(1) bond in 4 is
shorter than that in 1.
˚
Fig. 2. X-ray crystal structure determination of 4 selected bond length (A) and angles (°): Ni–C(1), 2.106(2); Ni–C(2), 2.155(3); Ni–C(3), 2.128(3); Ni–
C(4), 2.150(2); Ni–C(5), 2.160(2); Ni–P(1), 2.1358(7); Ni–C(20), 1.916(3); Ni–C(6), 1.269(3); N(1)–C(7), 1.425(3); C(20)–Ni–C(1), 96.12(10); C(20)–Ni–
C(3), 159.45(10); C(20)–Ni–P(1), 90.88(7); C(6)–N(1)–C(7), 123.7(2); C(5)–C(6)–C(19), 119.4(2); P(1)–Ni–C(2), 124.76(7); and C(20)–Ni–C(5), 105.60(10).

490
W.-P. Wei et al. / Inorganic Chemistry Communications 11 (2008) 487–491
Table 1
Results of styrene polymerization
Run
Catalyst
Al/Ni T (°C) Yield (%) Activity (ꢁ106 gPS/mol Ni h) Mv (ꢁ104 g/mol)d Mn (ꢁ104 g/mol)e Mw/Mn
Mn (g/mol)e
e,f
1a
2a
3a
4a
5b
6b
7b
8c
1
1
1
1
1
1
1
1
2
3
4
1000
1000
1000
1000
500
1000
1500
1000
1000
1000
1000
0
20
50
70
50
50
50
50
50
50
50
0
0
24.75
23.10
Trace
78.33
76.56
26.40
33.74
44.00
59.41
3.60
3.36
1.41
1.20
14.26
13.92
17.28
22.08
28.80
38.88
1.12
1.31
1.34
1.40
2.01
1.69
1.84
1.91
1.59
1.78
1405
1457
1219
1277
9c
10c
11c
a
Conditions: 0.25 lmol catalyst; styrene, 2.0 mL; polymerization time, 0.5 h; solvent, toluene (1 mL).
Conditions: 0.25 lmol catalyst; styrene, 2.5 mL; temperature, 50 °C; polymerization time, 0.5 h; solvent, toluene (1 mL).
b
c
d
e
f
Conditions: 0.25 lmol catalyst; styrene, 3.0 mL; temperature, 50 °C; polymerization time, 10 min; solvent, toluene (0.5 mL).
Obtained by capillary viscosimetry and calculated by Mark–Howink equation ½gꢂ ¼ 1:0 ꢁ 10ꢀ3M0v:5
.
Obtained by GPC.
Molecular distribution of the high molecular weight polymer.
To demonstrate what factors and how they may affect
ophenyl moieties in the cyclopentadienyl plane in 1. Lower
steric hindrance around central metal atom will be helpful
to the monomer to access the active species. This may be
the polymerization activity difference between 1 and 4. Fur-
ther polymerization mechanism is still under way.
the polymerization of styrene, the activities of catalyst
precursor 1 were investigated at different conditions for
that the ligand in 1 is a little different with that in other
three complexes, such as varied Al/Ni molar ratios and
polymerization temperature. The polymerization experi-
ment [12] results are summarized in Table 1. Temperature
influenced the catalytic performance of the polymerization
of styrene/1/MAO system. The catalyst 1 showed quite
good activity over a wide range (>50 °C) of polymeriza-
tion temperature. The activity increased with higher tem-
perature and reached a plateau around 50 °C. The
amount of MAO used in the complex 1-catalyzed styrene
polymerization reaction was critical for the catalyst to
exhibit high activity, and the optimal Al/Ni ratio was
1000. The activity reached as high as 14.26 ꢁ 106 gPS/
(molCat h). However, further increase of the Al/Ni ratio
impaired the activity of the catalyst. The explanation for
this was that the proper ratio of MAO to the complex
1, the formation and stabilization of the active species
was achieved; more MAO did not do attribution to the
polymerization activity [13]. The ligands linked on the
central nickel atom also play an important influence on
the styrene polymerization catalytic performance. With
the bigger iminoaryl-substitution on the cyclopentadienyl
group, the higher catalysis of the styrene polymerization
was found under the same condition. The highest catalytic
activity of the styrene/complex/MAO system is 4 with
38.88 ꢁ 106 gPS/molCat h. All the four complexes showed
higher styrene polymerization catalytic activities than that
reported in the literature [4e,5]. This can be attributed to
the structural difference between these complexes with
those reported. Due to the affection of N-phenyl-2,2,2-tri-
fluoroacetimidoyl group, the nickel atom is more electron
deficient. This enhances the catalytic activity a lot. Compar-
ing the structure of 1 and 4, lower steric hindrance of 4
around nickel atom was found for that there are two imin-
The polystyrene produced from the styrene/1–4/MAO
was bimodal, high Mw polymers (about 1–2 ꢁ 104) with a
narrow distribution (Mw/Mn < 2.0) and low Mw oligomers
(about 1300) as showed from GPC test result. This result is
almost same to the polymerization result of the literature
[5]. The iminoaryl-substituted cyclopentadienyl ligands
beard on the nickel atom did not influence the molecular
weight and distribution markedly. This may mean that cat-
alytic mechanism of the four complexes toward styrene
polymerization under the action of MAO is same. DSC
analysis result of the polystyrene shows that there is no
apparent melting point and glass transition temperature.
This accounts for that the structure of the polystyrene pro-
duced in these systems is random.
In summary,
a serial novel neutral phenylnickel
phosphine compounds bearing iminoaryl-substituted
cyclopentadienyl ligand were synthesized and character-
ized. Under the action of MAO, the complexes showed
high catalytic activity polymerization of styrene. Further
detailed investigation, including further investigation of
molecular structure, oligomers content in the polymer with
the polymerization condition, investigation of polymeriza-
tion mechanism is under way.
Appendix A. Supplementary material
Full tables of bond lengths and angles, tables of non-
hydrogen and hydrogen atomic coordinates and aniso-
tropic thermal parameters for non-hydrogen atoms. CCDC
625272, 632747 contain the supplementary crystallographic
data for 1 and 4. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via

W.-P. Wei et al. / Inorganic Chemistry Communications 11 (2008) 487–491
491
Cp-H), 1.96 (s, 6H, CH3). IR (KBr, cmꢀ1): 1590 (mC@N), 1438 (mP–C),
696 (mNi–P). MS, m/e (%) (EI): 399.1 (M+ꢀPPh3, 12.50%), 323.0
(M+ꢀPPh3ꢀPh, 5.31%), 264.1 (Ligand, 11.15%), 262.1 (PPh3,
100.00%). MS, m/e (%) (ESI): 1345.3 (2M++Na, 5.16%), 684.1
(M++Na, 20.03%), 662.1 (M+, 100.00%), 266.1 (Ligand+, 3.67%).
3: Yield: 73.24%. Melting point: 154–156 °C. Anal. calcd. for
http://www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.inoche.2008.01.006.
References
C
41H37F3NNiP: C, 71.33; H, 5.40; N, 2.03; Found: C, 71.56;
H, 5.30; N, 1.91. 1H NMR (C6D6, 500 MHz), d (ppm): 7.25–6.70
(m, 23H, Ph-H), 5.15 (s, 2H, Cp-H), 4.83 (s, 2H, Cp-H), 2.61 (s, 2H,
CH2 on the ethyl), 2.17 (d, 2H, CH2 on the ethyl), 1.08 (s, 6H, CH3 on
the ethyl). IR (KBr, cmꢀ1): 1621 (mC@N), 1434 (mP–C), 694 (mNi–P). MS,
m/e (%) (EI): 689.3 (M+, 1.53%), 427.2 (M+ꢀPPh3, 9.91%), 350.1
(M+ꢀPhꢀPPh3, 0.95%), 293.2 (Ligand, 8.39%). 4: Yield: 74.64%.
Melting point: 140–142 °C. Anal. calcd. for C43H41F3NNiP: C, 71.88;
[1] (a) P. Jutzi, Eur. J. Inorg. Chem. (1998) 663;
(b) U. Siemeling, Chem. Rev. 100 (2000) 1495;
(c) H. Butenschoen, Chem. Rev. 100 (2000) 1527;
(d) C. Mu¨ller, D. Vos, P. Jutzi, J. Organomet. Chem. 600 (2000) 127;
(e) Y. Qian, J. Huang, M.D. Bala, B. Lian, H. Zhang, H. Zhang,
Chem. Rev. 103 (2003) 2633.
1
H, 5.75; N,1.95; Found: C, 71.79; H, 5.75; N, 1.82. H NMR (C6D6,
[2] (a) L.K. Johnson, C.M. Killian, M. Brookhart, J. Am. Chem. Soc.
117 (1995) 6414;
500 MHz), d (ppm): 7.29–6.67 (m, 23H, Ph-H), 5.16 (s, 2H, Cp-H),
4.83 (s, 2H, Cp-H), 2.98 (s, 2H, CH of the isopropyl), 1.25 (s, 6H,
CH3 of the isopropyl), 0.93 (s, 6H, CH3 of the isopropyl). IR (KBr,
cmꢀ1): 1624 (mC@N), 1435 (mP–C), 694s (mNi–P). MS, m/e (%) (EI): 455.2
(M+ꢀPPh3, 11.72%), 397.3 (M+ꢀLigand, 8.38%), 378.2
(M+ꢀPhꢀPPh3, 2.34%), 321.2 (Ligand+, 4.54%), 262 (PPh3,
92.14%). MS, m/e (%) (ESI): 740.2 (M++Na, 100.00%), 718.2 (M+,
9.38%).
(b) B. Small, M. Brookhart, M.A. Alison, J. Am. Chem. Soc. 120
(1998) 4049;
(c) G.J.P. Britovsek, V.C. Gibson, S.J. McTavish, G.A. Solan, A.J.P.
White, D.J. Williams, G.J.P. Britovsek, B.S. Kimberley, P.J. Maddox,
Chem. Commun. (1998) 849;
(d) S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000)
1169.
[9] W. Zhao, Y. Qian, J. Huang, J. Duan, J. Organomet. Chem. 689
(2004) 2614.
[3] (a) C. Wang, S. Friedrich, T.R. Younkin, R.T. Li, R.H. Grubbs, D.A.
Bansleben, Mi.W. Day, Organometallics 17 (1998) 3149;
(b) T.R. Younkin, E.F. Connor, J.I. Henderson, S.K. Friedrich, R.H.
Grubbs, D.A. Bansleben, Science 287 (2000) 460;
(c) F.A. Hicks, M. Brookhart, Organometallics 20 (2001) 3217.
[4] (a) H. Yamazaki, N. Hagihara, Bull. Chem. Soc. Jpn. 37 (1964) 907;
(b) M.R. Churchill, T.A. O’Brien, J. Chem. Soc. A (1969) 266;
(c) A. Emad, M.D. Rausch, J. Organomet. Chem. 191 (1980) 313;
(d) F. Scott, S. Cronje, H.G. Raubenheimer, J. Organomet. Chem.
326 (1987) C40;
[10] Crystal data for 1: C45H33F6N2NiP, Mr=805.41, 0.135 ꢁ 0.121 ꢁ
˚
0.060 mm,
monoclinic,
P2(1)/n,
a = 13.9294(10) A,
b =
˚
˚
14.9974(11) A, c = 19.2768(13) A, a = 90°, b = 109.668(2)°, c = 90°,
V = 3792.1(5) A , F(000) = 1656, Z = 4, Dcalcd = 1.411 Mg/m3,
3
˚
22,136 reflections collected, 8271 unique reflections used in all
calculations, R(wR) = 0.0591, goodness of fit 0.663. Crystal data for
4: C43H41F3NNiP, Mr = 718.45, 0.503 ꢁ 0.432 ꢁ 0.337 mm, triclinic,
ꢀ
˚
˚
˚
P1, a = 10.4593(13) A, b = 15.3556(19) A, c = 23.961(3) A, a =
3
˚
83.018(2)°,
b = 86.517(2)°,
c = 74.598(2)°,
V = 3681.0(8) A ,
(e) E. Ihara, T. Fujimura, et al., J. Polym. Sci. Part A: Polym. Chem.
38 (2000) 4764.
[5] (a) L.F. Groux, D. Zargarian, R. Vollmerhaus, Organometallics 19
(2000) 1507;
F(000) = 1504, Z = 4, Dcalcd = 1.296 Mg/m3, 21,604 reflections col-
lected, 15,590 unique reflections used in the calculations, R1 = 0.0781,
wR2 = 0.0980, goodness of fit 0.829. Data were collected on a Bruker
SMART APEX diffractometer/CCD area detector, using mono-
(b) L.F. Groux, D. Zargarian, Organometallics 20 (2001) 3811;
(c) L.F. Groux, D. Zargarian, Organometallics 22 (2003) 3124;
(d) L.F. Groux, D. Zargarian, Organometallics 22 (2003) 4759;
(e) D. Gareau, C. Sui-Seng, L.F. Groux, F. Brisse, D. Zargarian,
Organometallics 24 (2005) 4003;
˚
chromated Mo Ka radiation, k = 0.71073 A at 293 K. The structures
are solved using direct methods and refined on F2 by fullmatrix least-
squares methods using the SHELX 97 program package.
[11] (a) D. Zhang, G. Jin, L. Weng, F. Wang, Organometallics 23 (2004)
3270;
(f) Davit Zargarian, Coord. Chem. Rev. 233–234 (2002) 157.
[6] K. Tamura, H. Mizukami, K. Maeda, H. Watanabe, K. Uneyama,
J. Org. Chem. 58 (1993) 32.
[7] A. Do¨hring, J. Go¨hre, P.W. Jolly, B. Kryger, J. Rust, G.P.J.
Verhovnik, Organometallics 19 (2000) 388.
[8] Compound 1: Yield: 71.98%. Melting point: 174–176 °C. Anal. calcd.
for C45H33F6N2NiP: C, 67.11; H, 4.13; N, 3.48; Found: C, 66.83;
H, 4.12; N, 3.36. The 1H NMR analysis cannot give a satisfactory
result due to the low solubility of 1 in C6D6. IR (KBr, cmꢀ1): 1623
(mC@N), 1435 (mP–C), 694 (mNi–P). MS, m/e (%) (EI): 542 (M+–PPh3,
10.73%), 465 (M+–PPh3–Ph, 1.58%), 407 (Ligand, 1.63%), 292
([Ni + Cp(CF3)C@NPh]+, 1.10%), 262 (PPh3, 100.00%), 216 ([Ni +
Cp(CF3)C@N]+, 1.54%). MS, m/e (%) (ESI): 827.1 ([M++Na]+,
76.44%), 805.1 (M+, 13.79%). 2: Yield: 62.38%. Melting point: 138–
140 °C. Anal. calcd. for C39H33F3NNiP: C, 70.72; H, 5.02, N, 2.11;
Found: C, 70.62; H, 4.74; N, 2.02. 1H NMR (C6D6, 500 MHz),
d (ppm): 7.17–6.71 (m, 23H, Ph-H), 5.15 (s, 2H, Cp-H), 4.82 (s, 2H,
(b) S.Y. Desjardins, K.J. Cavell, J.L. Hoare, B.W. Skelton, A.N.
Sobolev, W.A. White, W. Keim, J. Organomet. Chem 554 (1997)
163.
[12] In a Schlenk flask, catalyst was dissolved in toluene (1 lmol/mL).
Styrene (different volume) was added and finally cocatalyst in molar
ratios of 100, 500 or 700. The mixture was kept for different time at
constant temperature. Then, ethanol/HCl (5%) solution was added to
interrupt reaction. The mixture was filtered, and the polymer
extracted from the solid residue using toluene. After solvent evapo-
ration, polymers were dried under vacuum.
[13] (a) S. Koltzenburg, J. Mol. Catal. A: Chem. 116 (1997) 355;
(b) L. Jiang, Z. Shen, Y. Zhang, Eur. Polym. J. 36 (2000) 2513;
(c) J. Huang, Z. Feng, H. Wang, Y. Qian, J. Sun, Y. Xu, W. Chen,
G. Zheng, J. Mol. Catal. A: Chem. 189 (2002) 187;
(d) M. Zhou, S. Zhang, H. Tong, W. Sun, D. Liu, Inorg. Chem.
Commun. 10 (2007) 1262.