Copolymerization of ethylene with acrylonitrile promoted by novel nonmetallocene catalysts with phenoxy-imine ligands

Article abstract of DOI:10.1002/pola.25981

A series of novel nonmetallocene catalysts with phenoxy-imine ligands was synthesized by the treatment of phthaldialdehyde, substituted phenol with TiCl₄, ZrCl₄, and YCl₃ in THF. The structures and properties of the catalysts were characterized by ¹H NMR and elemental analysis. These catalysts were used for copolymerization of ethylene with acrylonitrile after activated by methylaluminoxane (MAO). The effects of copolymerization temperature, Al/M (M = Ti, Zr, and Y) ratio in mole, concentrations of catalyst and comonomer on the polymerization behaviors were investigated in detail. These results revealed that these catalysts were favorable for copolymerization of ethylene with acrylonitrile. Cat.3 was the most favorable one for the copolymerization of ethylene with acrylonitrile, and the catalytic activity was up to 2.19 × 10⁴ g PE/mol.Ti.h under the conditions: polymerization temperature of 50 °C, Al/Ti molar ratio of 300, catalyst concentration of 1.0 × 10^-4 mol/L, and toluene as solvent. The resultant polymer was characterized by FTIR, cross-polarization magic angle spinning, ¹³C NMR, WAXD, GPC, and DSC. The results confirmed that the obtained copolymer featured high-weight-average molecular weight, narrow molecular weight distribution about 1.61-1.95, and high-acrylonitrile incorporation up to 2.29 mol %. Melting temperature of the copolymer depended on the content of acrylonitrile incorporation within the copolymer chain.

Full text of DOI:10.1002/pola.25981

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Copolymerization of Ethylene with Acrylonitrile Promoted by Novel
Nonmetallocene Catalysts with Phenoxy-Imine Ligands
Xinli Zhang,1 Zhi Liu,1 Jianjun Yi,2 Fengjiao Li,1 Haibing Huang,1 Wei Liu,1 Hongpeng Zhen,1
Qigu Huang,1 Kejing Gao,2 Wantai Yang1
1State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers,
Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China
2Laboratory for Synthetic Resin Research Institution of Petrochemical Technology, China National Petroleum Corporation,
Beijing 100083, China
Correspondence to: Q. Huang (E-mail: qgh96@yahoo.com.cn) or W. Yang (E-mail: huangqg@mail.buct.edu.cn)
Received 12 December 2011; accepted 1 February 2012; published online 23 February 2012
DOI: 10.1002/pola.25981
ABSTRACT: A series of novel nonmetallocene catalysts with phe-
noxy-imine ligands was synthesized by the treatment of phthal-
dialdehyde, substituted phenol with TiCl4, ZrCl4, and YCl3 in
THF. The structures and properties of the catalysts were charac-
terized by 1H NMR and elemental analysis. These catalysts were
used for copolymerization of ethylene with acrylonitrile after
activated by methylaluminoxane (MAO). The effects of copoly-
merization temperature, Al/M (M ¼ Ti, Zr, and Y) ratio in mole,
concentrations of catalyst and comonomer on the polymeriza-
tion behaviors were investigated in detail. These results
revealed that these catalysts were favorable for copolymeriza-
tion of ethylene with acrylonitrile. Cat.3 was the most favorable
one for the copolymerization of ethylene with acrylonitrile, and
the catalytic activity was up to 2.19 ꢀ 104 g PE/mol.Ti.h under
the conditions: polymerization temperature of 50 ꢁC, Al/Ti molar
ratio of 300, catalyst concentration of 1.0 ꢀ 10–4 mol/L, and tolu-
ene as solvent. The resultant polymer was characterized by
FTIR, cross-polarization magic angle spinning, 13C NMR, WAXD,
GPC, and DSC. The results confirmed that the obtained copoly-
mer featured high-weight–average molecular weight, narrow
molecular weight distribution about 1.61–1.95, and high-acrylo-
nitrile incorporation up to 2.29 mol %. Melting temperature of
the copolymer depended on the content of acrylonitrile incorpo-
C
V
ration within the copolymer chain. 2012 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 50: 2068–2074, 2012
KEYWORDS: acrylonitrile; copolymer; ethylene; methylaluminox-
ane; nonmetallocene catalyst; structure
INTRODUCTION Traditional supported Ziegler–Natta catalyst
and homogenous Ziegler–Natta catalysts such as metallocene
catalyst and nonmetallocene catalyst are excellent for olefins
(co-)polymerization.1–4 However, it is challenging for the
coordination copolymerization of ethylene with polar como-
nomer, because the nonbonded electron pair of the heteroa-
tom from the polar comonomer tends to form complex with
the center metal, resulting in that the transition metal cata-
lyst is deactivated. So far, copolymers of ethylene with polar
monomers mainly have been prepared by conventional radi-
cal process, which has poor stereo-controlling ability for
polymers.5 Thus, a preferred approach for the synthesis of
functional polyolefins is the use of nonmetallocene catalyst,
by changing the ligand structure of the catalyst to make the
center metal less oxophilicit and to enhance the stereo-con-
trolling ability for polymer. Fujita6 reported highly selective
formation of Al-PEs prepared by a bis(phenoxy-imine)Zr
complex with methylalumoxane, which confirmed that the
stereo-controlling ability of the nonmetallocene catalysts can
be enhanced, and the molecular tailoring of polymer can be
realized by changing ligand structure. Ye7 prepared a series
of new titanium complexes with two asymmetric bidentate
b-enaminoketonato (N,O) ligands for ethylene polymeriza-
tion. By changing the groups on benzene ring of the ligands,
ethylene polymerization behavior was considerably influ-
enced. Liu8 synthesized a series of titanium complexes bear-
ing phenoxy-phosphine or thiphenoxy-phosphine ligands,
which efficiently promoted copolymerization of ethylene
with methyl 10-undecenoate. In 2007, Nozaki9 synthesized
ethylene-rich linear copolymers of ethylene with acrylonitrile
by isolated phosphine-sulfonate methylpalladium complex. It
was observed for the first time that acrylonitrile units were
inserted into a linear polyethylene chain. He found that acry-
lonitrile units were not only at the terminating end of the co-
polymer chain but also in the backbone. In 2009, Nozaki10
reported copolymerization of ethylene with vinyl acetate pro-
moted by Pd/alkylphosphine sulfonate catalyst, resulting in
highly linear copolymers possessing in-chain and chain-end
C
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VAc units. In 2010, Nozaki11 continued to research the rea-
son why incorporation of acrylonitrile to a linear polyethyl-
ene became possible using the phosphine-sulfonato Pd com-
plex. He found that the P-SO3 ligand facilitated both
acrylonitrile insertion to alkyl Pd and ethylene insertion to
a-cyanoalkyl Pd and that the b-hydride elimination was rea-
sonably suppressed with PASO3. More important was that
the experiment of ethylene/acrylonitrile copolymerization
was realized by using the NAO/Pd complex with high-cata-
lyst loading. This is a significant indication that the catalysts
with NAO ligand highly promoting ethylene/acrylonitrile
copolymerization would be possible. In 2010, Mecking12
demonstrated that copolymerization of ethylene with acrylic
acid was successful using neutral palladium(II) phosphine-
sulfonato catalysts. Herein, we reported a kind of novel non-
metallocene catalysts bearing two phenoxy-imine groups that
was used for copolymerization of ethylene with acrylonitrile
with high-catalytic activity. The obtained copolymers fea-
tured narrow MWD, high-molecular weight (MW), and high-
comonomer incorporation content. The effects of the ligand
structures and the center metal atoms (Ti, Zr, and Y) of these
catalysts and the polymerization conditions such as tempera-
ture, Al/M (M ¼ Ti, Zr, and Y) ratio in mole and concentra-
tions of catalyst and comonomer on the polymerization
behaviors were investigated.
75.432. Repetition delay for CP-MAS experiment was 10 s
pulse sequence. The pulse width for excitation was 3.3 ls.
The spectrum width of scanning was 350 ppm, and scanning
times were 500–1000. The cross-polarization time of 13C
and 1H was 3 ms. Typical spinning rate used for MAS and
CP–MAS experiment was 5 kHz. The 13C chemical shift was
referenced to external TMS. The acrylonitrile incorporation
content was estimated from CP-MAS 13C NMR spectra. The
average MW and molecular weight distribution (MWD) were
measured by PL-GPC200 instrument using standard polyeth-
ylene as reference and 1,2,4-trichlorobenzene as solvent at
ꢁ
150 C. DSC thermograms were recorded with a PA5000-DSC
instrument at a rate of 10 K/min. WAXD curves were
recorded with a Rigaku D/max 3A instrument, using Ni films
to sieve wave, using Cu Ka radiation (k ¼ 1.5405 ꢀ 10ꢂ10
m). WAXD intensities were recorded from 5ꢁ to 40ꢁ with a
continuous scanning speed.
Polymerization Procedure
All polymerization manipulations were carried out in a 300-
mL reaction flask after purging all moisture and oxygen by a
high-vacuum pump. Freshly distilled solvent (80 mL),
desired amount of catalysts (Cat.1–9), and MAO were intro-
duced in order. The mixture was stirred for 15 min for pre-
activation. Then injected desired amount of acrylonitrile
using as comonomer, charged ethylene up to desired pres-
sure, and heated the reactor to desired temperature. The
system was stirred for 10 min. Finally, the reaction was ter-
minated with 10 wt % HCl in alcohol. The obtained product
was filtered, washed, then dried to constant weight in a vac-
uum oven at 80 ꢁC, weighted it, and calculated the catalytic
activity.
EXPERIMENTAL
General Remarks
All operations of air- and moisture-sensitive materials were
performed using the rigorous repellency of oxygen and mois-
ture in flamed Schlenk-type glassware on a dual manifold
Schlenk line under nitrogen atmosphere. Phthaldialdehyde
(99%) was purchased from J&K in China; 2-amino-4-methyl-
phenol (98%) was purchased from TCI in China; 2-amino-5-
methylphenol (98%) was purchased from Aldrich in China;
2-amino-4-t-butylphenol (97%) and methylaluminoxane
(MAO) with 10 wt % in toluene were purchased from Acros
Organics Agent in China. Toluene and THF from Beijing
Chemicals Company were further purified by refluxing over
sodium under normal pressures for 48 h prior use. Acryloni-
trile was stored in a Schlenk tube containing 5 Å molecular
sieves under high-purity nitrogen for 6 days prior use.
Synthesis of Catalyst Precursors
Phthaldialdehyde 0.68 g (5.0 mmol) and 2-amino-4-methyl-
phenol 1.26 g (10.0 mmol) were dissolved in anhydrous
ꢁ
alcohol of 50 mL. The mixture was refluxed for 8 h at 80 C.
Subsequently, the mixture was cooled to room temperature,
and the precipitate was obtained. Then the precipitate was
further purified by dissolved in anhydrous ether and recrys-
tallized at ꢂ10 ꢁC. About 1.48 g of L1 with yield of 86.0%
1
Characterization
was obtained (Scheme 1), H NMR (DMSO-d6): d 2.48 (s, 6H,
1H NMR spectra were recorded on a Variꢁan INOVA600 MHz
spectrometer in DMSO-d6 solution at 25 C, and tetramethyl
silane (TMS) was used as reference. All 1H chemical shifts
were reported in parts per million relative to proton reso-
nance in DMSO-d6 at d 2.62 ppm. Elemental analyses were
performed on a Perkin–Elmer 2400 microanalyzer. FTIR
spectra were recorded by a Nicolet 5DXC FTIR spectrograph.
The spectra were obtained at a 40 cmꢂ1 resolution, and av-
erage data were obtained from at least 32 scans in the
standard wave number range from 500 to 4000 cmꢂ1. The
instrument using for solid-state 13C NMR was AV-300 system
(Bruker) of 7.05 T and a multinuclear cross-polarization
magic angle spinning (CP-MAS) probe. The diameter of zirco-
nia rotor was 4 mm. The resonance frequency of 13C was
methyl on benzene), d 6.15–7.63 (m, 10H, benzene), d 8.19
(s, 2H, CH¼¼N), d 8.97 (s, 2H, OH); L1 (C22H20N2O2, FW
¼
344), ELEM. ANAL. Calcd: C, 76.81; H, 5.81; N, 8.14; found: C,
76.79; H, 5.83; N, 8.11. Ti complex of L1 (Cat.1) was pre-
pared by the treatment of L1 0.35 g (1.0 mmol) with TiCl4
(0.11 mL, 1.0 mmol) in THF of 50 mL at 0 ꢁC, adding Et3N
ꢁ
of 2.0 mmol. The reaction was lasted for 6 h at 40 C. After
filtrated, the solvent was removed, and the residue was dried
by vacuum. Cat.1 was obtained (0.39 g, 64.6%; Scheme 1).
Cat.1 was confirmed by 1H NMR and microanalysis (Table
1). The ligand L2 derived from 2-amino-5-methylphenol, L3
from 2-amino-4-t-butylphenol, and Cat.2–9 were synthesized
according to the similar method mentioned earlier. Their 1H
NMR and microanalysis data were compiled in Table 1.
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exhibited lower affinity ability to the polar functional group,
giving rise to an enhanced catalytic activity. As showed in Ta-
ble 2, different ligand structures of the complexes consider-
ably influenced the copolymerization behavior of ethylene
with acrylonitrile. The catalysts with L3 exhibited higher ac-
tivity (runs 3, 6, and 9 in Table 2). For example, the catalytic
activity of Cat.3 was 1.77 ꢀ 104 g PE/mol.Ti.h (run 3 in Ta-
ble 2), which was much higher than that of Cat.1 and Cat.2.
It might be ascribed to the bulk electron-donating group of
tertiary butyl. The electron effectivity, caused by the ligand
with tertiary butyl, resulted in an increase in electron den-
sity around Ti metal center, which reduced the ability for ti-
tanium to chelate with nitrogen atom from the comonomer,
and thus the Ti complex can bear heteroatoms better. In
addition, the steric effectivity of both the benzene ring
around the active center, and the tertiary butyl could prevent
the polar group (ACN) from chelating with metal centre.13
Therefore, Cat.3 exhibited the highest catalytic activity. And
the MW of the obtained copolymer catalyzed by Cat.3 was
also higher.
SCHEME 1 Synthesis of the nonmetallocene catalysts (the cat-
alyst contains two chlorine atoms when M ¼ Ti and Zr; while
contains only one chlorine atom when M ¼ Y).
From Table 2, it can be noticed that the center metal atom
of these catalysts also had remarkable influences on the
copolymerization of ethylene with acrylonitrile. Compared to
Ti and Zr complexes (Cat.1–Cat.6), Y complexes (Cat.7–Cat.9)
exhibited the lowest catalytic activity. Chemical bonds of
most lanthanide complexes conventionally belong to electro-
valent bonds with certain covalent characteristics.13,14 This
attributes to that 4f orbitals that play only a small role in
forming the rare earth compound bonds, thus yttrium atom
in the catalyst features strong oxophilicity. Apparently, it is
much easier for yttrium atom to chelate with nitrogen atom
from nitrile group (ACN) to form more steady complexes,15
which led to a decrease in the catalytic activity of yttrium
complexes. Compared to the Zr complexes, the Ti complexes
RESULTS AND DISCUSSION
Copolymerization of Ethylene with Acrylonitrile
The novel nonmetallocene catalysts (Cat.1–9) were used for
copolymerization of ethylene with acrylonitrile, using MAO
as cocatalyst. The effects of the catalyst ligand structures
and center metal atoms (Ti, Zr, and Y) on the copolymeriza-
tion of ethylene with acrylonitrile were compiled in Table 2.
Compared to ethylene homopolymerization, the catalytic ac-
tivity of copolymerization of ethylene with acrylonitrile was
much lower. As expected, acrylonitrile was poisonous for the
novel nonmetallocene catalysts system. However, a more
electron-donating and higher steric hindrance ligand would
be able to generate a less electrophilic metal center, which
TABLE 1 The Parameters for Cat.1 to Cat.9
Catalysts Metals Ligands Microanalysis
1H NMR
Cat.1
Cat.2
Cat.3
Cat.4
Cat.5
Cat.6
Cat.7
Cat.8
Cat.9
Ti
Ti
Ti
Zr
Zr
Zr
Y
L1
L2
L3
L1
L2
L3
L1
L2
L3
(C22H18N2O2TiCl2) (461): Calcd.
3.90, N 6.08; Found C 57.29, H 3.91, N 6.11.
22H18N2O2TiCl2) (461): Calcd. 57.32,
3.90, N 6.08; Found C 57.30, H 3.89, N 6.09.
(C28H30N2O2TiCl2) (545): Calcd. 62.85,
5.94, N 4.89; Found C 62.87, H 4.88, N 4.90.
C22H18N2O2ZrCl2) (504): Calcd. 52.39,
3.57, N 5.55; Found C 52.41, H 3.56, N 5.57.
22H18N2O2ZrCl2) (504): Calcd. 52.39,
3.57, N 5.55; Found C 52.40, H 3.58, N 5.54.
C
57.32,
H
(DMSO): d ¼ 2.51 (s, 6H, methyl on benzene), 6.18–
7.66 (m, 10H, benzene), and 8.22 (s, 2H, CH¼N)
C
C
H
(DMSO): d ¼ 2.53(s, 6H, methyl on benzene), 6.78–
7.82 (m,10H, benzene), and 8.22 (s, 2H, CH¼N)
C
H
(DMSO): d ¼ 1.33 (s, 18H, t-butyl on benzene), 6.17–
7.69 (m, 10H, benzene), and 8.20 (s, 2H, CH¼N)
C
H
(DMSO): d ¼ 2.50 (s, 6H, methyl on benzene), 6.18–
7.67 (m, 10H, benzene), and 8.21 (s, 2H, CH¼N)
C
C
H
(DMSO): d ¼ 2.52(s,6H, methyl on benzene), 6.77–
7.82 (m,10H, benzene), and 8.21(s, 2H, CH¼N).
(C28H30N2O2 ZrCl2) (588): Calcd. C 57.20, H (DMSO): d ¼ 1.32 (s, 18H, t-butyl on benzene), 6.16–
5.10, N 4.76; Found C 57.23, H 5.15, N 4.71.
7.69 (m, 10H, benzene), and 8.21 (s, 2H, CH¼N)
(C22H18N2O2YCl) (467): Calcd. C 56.58, H 3.85, (DMSO): d ¼ 2.51(s,6H, methyl on benzene), 6.17–
N 6.00; Found C 56.49, H 3.87, N 6.02.
7.66 (m, 10H, benzene), and 8.21 (s, 2H, CH¼N)
(C22H18N2O2YCl) (467): Calcd. C 56.58, H 3.85, (DMSO): d ¼ 2.54 (s, 6H, methyl on benzene), 6.77–
N 6.00; Found C 56.62, H 3.84, N 5.99.
7.83 (m, 10H, benzene), and 8.21 (s, 2H, CH¼N).
(C28H30N2O2YCl) (551): Calcd. C 61.03, H 5.44, (DMSO): d ¼ 1.34 (s, 18H, t-butyl on benzene), 6.17–
N 5.08; Found C 61.05, H 5.49, N 5.11.
7.70 (m, 10H, benzene), and 8.22 (s, 2H, CH¼N)
Y
Y
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TABLE 2 Effects of the Metal Atoms and Structures of Catalyst Ligands on Copolymerization of Ethylene
with Acrylonitrile
Aa (ꢀ10ꢂ4
)
Mw (ꢀ10ꢂ4
)
Mw/Mn
Tm (ꢁC)
Acry. Cond (mol %)
b
b
c
Run
Catalysts
1
2
3
4
5
6
7
8
9
a
Cat.1 (Ti)
Cat.2 (Ti)
Cat.3 (Ti)
Cat.4 (Zr)
Cat.5 (Zr)
Cat.6 (Zr)
Cat.7 (Y)
Cat.8 (Y)
Cat.9 (Y)
1.45
1.28
1.77
0.76
0.52
0.95
Trace
0.17
0.38
3.01
3.35
3.19
2.02
2.39
1.85
–
1.83
1.80
1.88
1.79
1.81
1.84
–
127.5
127.6
125.8
123.9
123.4
122.5
–
0.94
0.93
1.39
2.18
2.11
2.26
–
0.92
1.05
1.77
1.82
108.7
112.5
2.28
2.25
Catalytic activity, g P/mol.M.h.
Determined by GPC.
Determined by DSC.
Acrylonitrile incorporation content, determined by 13C NMR;
mol/L; ethylene pressure, 0.2 MPa; acrylonitrile, 0.3 mol/L; tem-
perature, 50 ꢁC; n(Al)/n(M), 300; solvent, toluene, 80 mL; time,
10 min.
b
c
d
polymerization conditions: concentration of catalyst, 1.0 ꢀ 10ꢂ4
exhibited better ability to bear heteroatoms, and so the cata-
lytic activity of the Ti complexes was higher for the copoly-
merization of ethylene with acrylonitrile.
reaction temperature from 40 to 60 ꢁC, the MW of obtained
copolymers decreased gradually and MWDs became broader
slightly. A possible explanation is that the weight–average
MW of the obtained copolymers is determined by the ratio
of Kp/Ktr. With the increasing of the polymerization tempera-
ture, Ktr increases faster than Kp. Therefore, rate of chain-
transfer to monomer and MAO enhances much more than
propagation reaction. However, acrylonitrile incorporation
within copolymer chain changed slightly with varying tem-
perature for Cat.3, which indicated that the reaction temper-
ature was not an important factor to control the incorpora-
tion of acrylonitrile.
The effects of polymerization conditions such as reaction
temperature, Al/Ti ratio, and concentrations of catalyst and
acrylonitrile on ethylene (co-)polymerization catalyzed by
Cat.3 were investigated. The results were listed in Table 3.
As shown in Table 3, with an increase of reaction tempera-
ture, the catalytic activity enhanced and reached the highest
4
ꢁ
value of 1.77 ꢀ 10 gPE/molTi.h (run 3 in Table 3) at 50 C
and then decreased. It might attribute to that the tempera-
ture not only influences polymerization rate constant but
also affects the concentration of monomer and stability of
the activity center.16 As seen in Table 3, with an increase of
The Al/Ti molar ratio influenced the catalytic activity
strongly. When the Al/Ti molar ratio ranged from 200 to
TABLE 3 Effects of Polymerization Conditions on Copolymerization of Ethylene with Acrylonitrile Catalyzed with
Cat.3
e
f
Cb
(ꢀ104)
Acryc
Mw
Tm
Acry. Cong
(mol %)
e
Run
Ta (ꢁC)
n(Al):n(Ti)
(mol/L)
Ad (ꢀ10ꢂ4
)
(ꢀ10ꢂ4
)
Mw/Mn
(ꢁC)
10
3
40
50
60
50
50
50
50
50
50
50
300
300
300
200
400
300
300
300
300
300
1.0
1.0
1.0
1.0
1.0
0.5
2.0
1.0
1.0
1.0
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0
1.49
1.77
1.15
1.39
1.16
1.36
1.13
102
2.19
1.38
f
3.51
3.19
2.58
2.97
1.95
3.45
2.76
78.9
3.65
2.72
1.83
1.88
1.91
1.90
1.96
1.79
1.90
1.61
1.81
1.95
126.5
125.8
124.8
125.2
124.3
126.1
125.3
134.5
127.3
123.1
1.34
1.39
1.41
1.43
1.44
1.35
1.41
–
11
12
13
14
15
16
17
18
a
0.1
0.5
0.96
2.29
Polymerization temperature.
Determined by DSC.
Acrylonitrile incorporation content, determined by 13C NMR;
b
c
g
Concentration of catalyst (mol/L).
Charged acrylonitrile concentration (mol/L).
Catalytic activity (g P/mol.Ti.h).
Determined by GPC.
polymerization conditions: ethylene pressure, 0.2 MPa; solvent,
toluene, 80 mL; time, 10 min.
d
e
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300 (runs 12 and 3 in Table 3), the catalytic activity
increased and reached the maximum value of 1.77 ꢀ 104
gPE/molTi.h at n(Al):n(Ti) ¼ 300 (run 3 in Table 3). The cat-
alytic activity decreased with further increasing the Al/Ti
molar ratio. The addition of MAO influenced the MWs and
MWDs of the obtained polymers. MAO as a cocatalyst acts as
a catalyst precursor for alkylation, a chain-transfer agent,
and a deimpurifier. Trimethylaluminum in MAO can reduce
oxidation state of Ti (IV) to Ti (III), while Ti (IV) is favorable
for a-olefin polymerization.17 When the amount of MAO is
smaller, part of active center is transferred to b-H, resulting
in lower activity, lower MWs, and broader MWDs. Although
when excess MAO is introduced, it might be easier for the
propagating chain transferring to MAO, resulting in lower
MWs and broader MWDs of the obtained polymers. So only
when the amount of MAO is proper, can the active center be
stable and chain transfer to b-H and MAO be controlled
effectively. Moreover, acrylonitrile incorporation within the
copolymers had minor changes with varying Al/Ti molar ra-
tio, which implied that the comonomer incorporation did not
mainly depend on the Al/Ti molar ratio.
FIGURE 1 Variation of melting temperature of polymers versus
acrylonitrile incorporation.
copolymers also decreased from 3.65 ꢀ 104, 3.19 ꢀ 104, to
2.72 ꢀ 104 g/mol upon increasing acrylonitrile concentration
in feed from 0.1, 0.3, to 0.5 m/L, respectively (runs 17, 3,
and 18 in Table 3) due to low rate of propagation reaction,
comparison with the chain transfer.18 The MWDs of the re-
sultant polymers almost kept about 2, indicating that the sin-
gle-site catalyst system was confirmed.
The catalytic activity for copolymerization of ethylene with
acrylonitrile exhibited the highest value of 1.77 ꢀ 104 g PE/
molTi.h under the catalyst concentration of 1.0 ꢀ 10–4 mol/
L. When the catalyst concentration changed from 0.5 ꢀ 10–4
to 1.0 ꢀ 10–4 mol/L (runs 14 and 3 in Table 3), the catalytic
activity increased from 1.36 ꢀ 104 to 1.77 ꢀ 104 g P/mol.-
Ti.h. But when the catalyst concentration further increased
to 2.0 ꢀ 10–4 mol/L (run 15 in Table 3), the catalytic activity
decreased to 1.13 ꢀ 104 g P/mol.Ti.h. It may attribute to
that when the catalyst concentration is lower than 1.0 ꢀ 10–
From Table 2, we can note that the melting temperatures of
the resultant polymers decreased with the decline of MWs,
but increased with the decline of the acrylonitrile contents
in the copolymers. For example, the two copolymers (runs 6
and 9ꢁ in Table 2) showed different melting temperatures,
4
mol/L, the number of activity species was smaller. Maybe a
ꢁ
122.5 C for run 6 and 112.5 C for run 9. Even though their
higher fraction of the activity species was poisoned by impu-
rity in the solution and inside the syringe. But if the catalyst
concentration was higher than 1.0 ꢀ 10–4 mol/L, the poly-
merization process became faster, which would lead to
greater amounts of polymer produced by the same-scale
manipulation at the same time. Therefore, the polymer chain
could be entangled easier, giving rise to decline in the overall
chain propagation rate. In addition, the catalyst concentra-
tion influenced the insertion content of acrylonitrile slightly,
implying that the comonomer incorporation was not mainly
depended on the concentration of the catalyst either.
acrylonitrile incorporation contents were almost the same,
2.26 mol % for run 6 and 2.25 mol % for run 9, they had
different MWs, 1.85 ꢀ 104 g/mol for run 6 and 1.05 ꢀ 104
g/mol for run 9. As shown in Figure 1 (the data from Table
3), DSC results showed that the melting temperatures of the
resultant polymers gradually decreased with increasing the
acrylonitrile contents of the copolymers, and only one melt-
ing temperature was observed, implying that the resultant
copolymer possessed uniform acrylonitrile incorporation.18
These results indicated that the melting temperatures of the
copolymers were influenced by MWs and acrylonitrile incor-
poration contents.
As shown in Table 3, the activity of cat.3 toward the copoly-
merization and comonomer incorporation was considerably
influenced by the comonomer feed ratios. With an increase
in the quantity of the acrylonitrile charged from 0.1, 0.3, to
0.5 m/L, the acrylonitrile contents of the copolymers
enhanced from 0.96, 1.39, to 2.29 mol %, respectively. But
the catalytic activity sharply decreased from 2.19 ꢀ 104,
1.77 ꢀ 104, to 1.38 ꢀ 104 g P/mol.Ti.h (runs 17, 3, and 18
in Table 3). Whereas the catalytic activity for ethylene homo-
polymerization was 1.02 ꢀ 106 g P/mol.Ti.h (run 16 in Table
3). The decline of catalytic activity might be ascribed to both
the low-insertion rate of the polar monomer and the last-
inserted functional a-olefin suppressing ethylene coordina-
tion and insertion. Similarly, the MWs of the resultant
Characterization of the Polymer
The CP-MAS 13C NMR spectrum of the polyethylene pro-
moted by Cat.3 (run 16 in Table 3) was carried out [Fig.
2(a)]. Only methylene peaks were recognizable in the spec-
tra. The peaks at d 33.7, 32.3, and 31.3 ppm were assigned
to methylene carbons from monoclinic crystalline, ortho-
rhombic crystalline, and amorphous fraction, respectively.19
Any other signals were not shown, which confirmed that the
obtained polymer was linear polyethylene without branch.
The CP-MAS 13C NMR spectrum of the copolymer of ethylene
with acrylonitrile (run 18 in Table 3) was presented in Fig-
ure 2(b). The weak signal at d 14–15 ppm exhibited the
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cene catalyst can also get polymer with saturated end group.
From Figure 2(b), we can see that there was no signal that
represented the unsaturated carbon–carbon double bond,
but a signal at d 14–15 ppm assigned to methyl was
observed, implying that the obtained copolymer of ethylene
with acrylonitrile, catalyzed by the catalyst system of Cat.3/
MAO, was featured with methyl group at the chain end. The
result confirmed that the dominant chain transfer was chain
transfer to MAO.
According to Figure 2(b), the area integral ratio of the reso-
nance peaks of methylene and methane (d ¼ 20–40 ppm) to
methyl group (d ¼ 14–15 ppm) was ꢃ486, which implied
that the copolymer molecular chain was comprised of 475
vinyl units and 11 acrylonitrile units. The number of acrylo-
nitrile units was calculated by the content of acrylonitrile
inserted into copolymer mentioned earlier. The vinyl unit of
475 was given by (486–11). Therefore, the number–average
MW (Mn) of the copolymer was calculated by the equation:
Mn ¼ 475 ꢀ 28 þ 11 ꢀ 53 ¼ 13,900 g/mol (28 is the MW
of ethylene, 53 is the MW of acrylonitrile), which was in
keeping with the result of GPC.
The FTIR plots of the obtained polymers were performed
(Fig. 3). The wave numbers at 2918, 2850, 1471, and 719
cmꢂ1 were characteristic of linear polyethylene. We can see
from the FTIR spectrums of the copolymers in Figure 3,
except for all the signals as same as polyethylene, there was
another signal near 2243 cmꢂ1 representing ACN group
within the copolymers of b, c, and d. The signal at 719 cmꢂ1
represented the long chain units [(CH2)n, n ꢄ 4] of polyethyl-
ene, but there was no signal at 719 cmꢂ1 for polyacryloni-
trile [Fig. 3(e)]. So, we can obtain the fraction of acrylonitrile
inserted into the copolymer chain by the ratio of integral
area of the absorption peak at 2243 cmꢂ1 to that at 719
FIGURE 2 CP-MAS 13C NMR spectra of (a) polyethylene from
run 16 in Table 3 and (b) ethylene/acrylonitrile copolymer from
run 18 in Table 3.
existence of ACH3, which was located at the end of the co-
polymer chain. The signals at 20–40 ppm represented meth-
ylene and methine of the copolymer backbone and that at
115–125 ppm represented the side group of ACN. The result
confirmed that acrylonitrile was inserted into the copolymer
chain indeed. The area integral ratio of the resonance peaks
of methylene, methane (d ¼ 20–40 ppm) to nitrile group (d
¼ 115–125 ppm) was 87.5:1. That was to say x/y ¼ (87.5–
2)/2 ¼ 85.5/2 ¼ 42.75/1. So, the content of acrylonitrile
that was inserted into copolymer was y/(x þ y) ¼ 1/(42.75
þ 1) ¼ 2.29 mol %, Where x was defined as the number of
ethylene units and y defined as the number of acrylonitrile
units within the copolymer chain.
There are two main patterns of chain transfer in the copoly-
merization process catalyzed by nonmetallocene catalyst.
One is that b-H transfers to active center and monomer; the
other is that the growing chain transfers to MAO. The former
obtains polymer with unsaturated end group, while the latter
obtains polymer with saturated end group. Chain termination
reaction of olefin polymerization catalyzed by nonmetallo-
FIGURE 3 FTIR spectrums of ethylene homopolymer (a, run 16
in Table 3) and ethylene/acrylonitrile copolymer (b, run 3 in Ta-
ble 3; c, run 17 in Table 3; d, run 18 in Table 3) and polyacrylo-
nitrile (e, obtained by radical polymerization, AIBN used as
initiator at 65 ꢁC for 4 h).
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cmꢂ1 [Fig. 3(b–d)]. As for the copolymer d [Fig. 3(d)], the ra-
tio of A2243/A719 was 0.335, where A2243 was defined as the
integral area of the absorption peak at 2243 cmꢂ1 and A719
was defined as the integral area of the absorption peak at
719 cmꢂ1. And we have calculated the acrylonitrile incorpo-
ration for the copolymer d was 2.29 mol %. For the copoly-
mers b and c [Fig. 3(b,c)], the ratios of A2243/A719 were
0.141 and 0.204, respectively. The acrylonitrile incorporation
of the copolymer d was used as reference; thus, the acryloni-
trile contents of the copolymer b and c were 0.96 and 1.39
mol %, respectively. Compared to polyacrylonitrile, the sig-
nals of ACN side group of the copolymers b, c, and d moved
toward blue area and became 2243.2, 2243.3, and 2243.6
cmꢂ1 (Fig. 3), respectively. The result revealed that the wave
number of ACN side group of the copolymer increased with
increasing the acrylonitrile incorporation content within the
copolymer chain.
tion from Beijing Municipal Education Commission (BNEC)
(XK100100540, XK100100640).
REFERENCES AND NOTES
1 Bialk, M.; Czaja, K. Polymer 2000, 41, 7899–7904.
2 Kong, Y.; Yi, J. J.; Dou, X. L.; Liu, W. J.; Huang, Q. G.; Gao,
K. J.; Yang, W. T. Polymer 2010, 51, 3859–3866.
3 Luo, H. K.; Tang, R. G.; Gao, K. J. J. Catal. 2002, 210,
328–339.
4 Huang, Q. G.; Sheng, Y. P.; Yang, W. T. J. Appl. Polym. Sci.
2007, 103, 501–505.
5 Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169–1204.
6 Saito, J.; Tohi, Y.; Matsukawa, N.; Mitani, M.; Fujita, T. Mac-
romolecules 2005, 38, 4955–4957.
7 Ye, W. P.; Zhan, J.; Pan, L.; Hu, N. H.; Li, S. Y. Organometal-
lics 2008, 27, 3642–3653.
CONCLUSIONS
8 He, L. P.; Hong, M.; Li, B. X.; Liu, J. Y.; Li, Y, S. Polymer
2010, 51, 4336–4339.
The novel nonmetallocene catalysts consisting of phenoxy-
imine ligands, Cat.1–Cat.9, exhibited high-catalytic activity
for the copolymerization of ethylene with acrylonitrile. Under
the typical polymerization condition: temperature of 50 ꢁC,
Al/Ti molar ratio of 300, concentration of catalyst with 1.0
ꢀ 10–4 mol/L, toluene as solvent, and the catalytic activity of
the copolymerization of ethylene with acrylonitrile was of up
to 2.19 ꢀ 104 g PE/molTi.h. Both the results of FTIR and
solid 13C NMR indicated that the structure of the obtained
polyethylene was linear and the copolymer of ethylene with
acrylonitrile catalyzed by Cat.3 had the highest acrylonitrile
incorporation content up to 2.29 mol %. Acrylonitrile units
within the copolymer chain were isolated by ethylene units.
Block distribution of ethylene units was dominant in the co-
polymer chain. The GPC results confirmed that the obtained
polymers featured higher MW up to 3.65 ꢀ 104 g/mol and
narrow Mw/Mn ratio within 2.
9 Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. J. Am. Chem.
Soc. 2007, 129, 8948–8949.
10 Ito, S.; Munakata, K.; Nakamura, A.; Nozaki, K. J. Am.
Chem. Soc. 2009, 131, 14606–14607.
11 Nozaki, K.; Kusumoto, S.; Noda, S.; Kochi, T.; Chung, L. W.;
Morokuma, K. J. Am. Chem. Soc. 2010, 132, 16030–16042.
12 Runzi, T.; Frohlich, D.; Mecking, S. J. Am. Chem. Soc. 2010,
132, 16623–16630.
13 Maron, L.; Eisenstein, O. J. Phys. Chem. A 2000, 104, 7140–7143.
ꢀ
14 Vicentini, G.; Zinner, L. B.; Aricoa, E. M.; Zinnera, K.; Matosa,
J. R.; De Matos, J. E. X. Thermochim. Acta 1993, 228, 137–146.
15 Terao, H.; Ishii, S.; Mitani, M.; Tanaka, H.; Fujita, T. J. Am.
Chem. Soc. 2008, 130, 17636–17637.
16 Ma, L.; Wang, H. L.; Yi, J. J.; Huang, Q. G.; Gao, K. J.; Yang,
W. T. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 417–424.
17 Huang, Q. G.; Wu, Q.; Zhu, F. M.; Lin, S. A. J. Polym. Sci.,
Part A: Polym. Chem. 2001, 39, 4068–4074.
Financial support for this work from the National Natural Sci-
ence Foundation of China (Grant No. 21174011), the Natural
Science Foundation of Beijing, China (Grant No. 2102036), and
Major Project for Polymer Chemistry, Physics Subject Construc-
18 Mu, J. S.; Liu, J. Y.; Liu, S. R.; Li, Y. S. Polymer 2009, 50,
5059–5064.
19 Hana, O. H.; Chaea, S. A.; Hanb, S. O.; Woob, S. K. Polymer
1999, 40, 6329–6336.
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