Copolymers of Ethylene and Vinyl Amino Acidic Ester with High Molecular Weight Prepared by Non-metallocene Catalysts

Article abstract of DOI:10.1007/s10562-015-1686-1

Non-metallocene catalysts containing [N, Si, N, P]-type ligands based on diphenyl phosphorus-phenylamine and their derivatives were synthesized and characterized by H(¹³C) NMR, ESI-MS and micro analysis. They were able to catalyze copolymerization of ethylene with N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester after activated by methylaluminoxane (MAO). Effects of transition metal atoms (Ti, Zr and Hf), ligand structures and polymerization conditions were investigated. The structures and properties of the obtained polymers were characterized by FT-IR, ¹³C NMR, GPC and DSC. The results indicated that the obtained copolymers had high weight average molecular weight of 2.70 × 10⁵ g/mol and high comonomer incorporation rate of 23.07 wt% within the copolymer chain. The melting temperature of the copolymer was up to 138.6 °C higher than that of the polyethylene.

Full text of DOI:10.1007/s10562-015-1686-1

Catal Lett
DOI 10.1007/s10562-015-1686-1
Copolymers of Ethylene and Vinyl Amino Acidic Ester with High
Molecular Weight Prepared by Non-metallocene Catalysts
Jing Wang1 Feng Nan1 Jiangping Guo1 Jian Wang2 Xianghui Shi1
•
•
•
•
•
Haibing Huang1 Qigu Huang1 Wantai Yang1
•
•
Received: 16 December 2015 / Accepted: 21 December 2015
Ó Springer Science+Business Media New York 2015
Abstract Non-metallocene catalysts containing [N, Si, N,
P]-type ligands based on diphenyl phosphorus-pheny-
lamine and their derivatives were synthesized and charac-
terized by H(13C) NMR, ESI–MS and micro analysis. They
were able to catalyze copolymerization of ethylene with
N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester after acti-
vated by methylaluminoxane (MAO). Effects of transition
metal atoms (Ti, Zr and Hf), ligand structures and poly-
merization conditions were investigated. The structures and
properties of the obtained polymers were characterized by
FT-IR, 13C NMR, GPC and DSC. The results indicated that
the obtained copolymers had high weight average molec-
ular weight of 2.70 9 105 g/mol and high comonomer
incorporation rate of 23.07 wt% within the copolymer
chain. The melting temperature of the copolymer was up to
138.6 °C higher than that of the polyethylene.
Graphical Abstract
Keywords Non-metallocene catalysts Á N-acetyl-O-(hex-
5-enyl)-L-tyrosine ethyl ester Á Copolymer
1 Introduction
Polyolefins, such as polyethylene and polypropylene, are
the most widely used polymers in a broad range of com-
mercial applications. In recent decades, considerable
attention has been paid to synthesis of new polyolefins with
high performance or functionality. Ziegler–Natta catalysts
can catalyze the polymerization of olefins efficiently.
However, coordination copolymerization of ethylene with
polar comonomers can not be realized by using Ziegler–
Natta catalyst system because the active site is easy to be
poisoned by electron-donating atoms from the polar
comonomers, such as N, O, S, P, etc [1–7]. Metallocene
& Qigu Huang
huangqg@mail.buct.edu.cn
1
State Key Laboratory of Chemical Resource Engineering,
Key Laboratory of Carbon Fiber and Functional Polymers,
Ministry of Education, The College of Material Science and
Engineering, Beijing University of Chemical Technology,
Beijing 100029, China
2
Liaoyang Petrochemical Corporation, China National
Petroleum Corporation, Liaoyang 111003, China
123

J. Wang et al.
catalysts can catalyze polymerization of limited polar
monomers, but the catalytic activity decreases dramatically
[8]. So far, copolymers of ethylene with polar monomers
mainly have been prepared by conventional radical pro-
cess, which needs harsh technology with high pressure and
high temperature [9]. Non-metallocene catalysts can cat-
alyze copolymerization of olefins with polar comonomers
containing N, O, S and other heteroatoms because this kind
of catalyst possesses broad ‘‘tolerance’’ to the electron-
donating atoms, so design of non-metallocene catalysts has
attracted much attention. Marks [10] adopted CGCTiMe2/
Ph3CB?(C6F5)-4 to catalyze the copolymerization of ethy-
lene with 5-hexenylsilane, functional group was introduced
to the copolymer. The results showed that 5-hexenylsilane
readily underwent insertion into the polymer chain as well
as effects intramolecular chain termination. Palladium
complexes with bulky substituted a-diimine ligands can
catalyze the copolymerization of ethylene and a-olefins
with methyl acrylate to give high-molar-mass polymers
[11]. Mecking et al. [12] prepared copolymer of ethylene
with acrylamide by employing palladium complexes as
catalyst precursor. They also demonstrated that copoly-
merization of ethylene with acrylic acid was successful by
using neutral palladium (II) phosphine-sulfonato catalysts.
[13] Titanium complexes bearing phenoxy-phosphine or
thiphenoxy-phosphine ligands promoted copolymerization
of ethylene with methyl 10-undecenoate efficiently. [14] In
2007, Nozaki et al. [15] synthesized linear copolymers of
ethylene with acrylonitrile by isolated phosphine-sulfonate
methyl palladium complex. It was observed that acryloni-
trile units were inserted into not only at the terminating end
of the copolymer chain but also in the backbone. In the
following years, Nozaki et al. prepared copolymers of
ethylene with various polar monomers such as allyl
monomers [16], vinyl acetate [17] etc. by palladium/
phosphine-sulfonate catalyst. Furthermore, they utilized
palladium/alkylphosphine—sulfonate catalyst to synthesize
copolymers of ethylene with polar monomers featured with
higher weight average molecular weight of 1.77 9
105 g/mol by tuning the substitunent groups of phosphorus
atom consisting of the ligand [18].
to 10 mol% in the copolymer. In our previous work,
non-metallocene catalysts with [N, N, O] [22], [N, N, N]
[23] and [N, N, O, O] [24, 25] ligands were synthesized and
carried out for polymerization of ethylene and copolymer-
ization of ethylene with a-olefins or polar monomer such as
acrylonitrile. In generally, dimer, trimer, or oligomer of
amino acid can be synthesized by condensation polymer-
ization. Many polymerization techniques, such as ring-
opening metathesis polymerization (ROMP), acyclic diene
metathesis (ADMET) and atom transfer radical polymer-
izations (ATRP) are not efficient for copolymerization of
ethylene with polar monomers. Kim et al. [26] recently
reported that polyethylene drug delivery nanocapsules
consisting of polyethylene and poly(ethylene glycol)106
-
b-poly(propylene glycol)70-b-poly(ethylene glycol)106
copolymer was obtained by self-assembled to capsule
paclitaxel. Polyamino esters are a promising alternative for
clinical applications used as polymeric vectors for gene
delivery, as they are generally safer than viral counterparts.
[27] The copolymers with bioactive groups have been taken
much attraction due to their outstanding potential applica-
tions in pharmacological and biological fields used as inviral
vectors [28, 29].
Herein, we reported that the copolymers of ethylene
with N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester pre-
pared by non-metallocene catalysts with [N, Si, N, P]-
type ligands based on diphenyl phosphorus-phenylamine
and their derivatives. The copolymers with pendent
bioactive groups should have new properties due to
hydrophilic side chain being compatibilic with tissues and
hydrophobic backbone being compatibilic with many
hydrophobic drugs.
2 Experimental
2.1 General Remarks
Aniline (99.8 %), N-acetyl-L-tyrosine ethyl ester (99 %) and
6-bromo-1-hexene (97 %) were purchased from J&K in Bei-
jing, China. 2,4,6-trimethylaniline (99 %), dichlorodimethyl-
silane (99.8 %),diphenyldichlorosilane (97 %), 2,4,6-trifluo-
roaniline (97 %), methylmagnesium chloride (CH3MgCl)
with 22 wt% in THF and MAO with 10 wt% in toluene were
purchased from Acros Organics Agent in Shanghai, China.
Chlorodiphenylphosphine (99 %)was purchased from Strem
Chemicals in Beijing, China. Toluene, n-hexane, acetone and
diethyl ether were from Beijing Chemicals Company in Bei-
jing, China. Toluene and n-hexane were further purified by
refluxing over sodium under normal pressure for 48 h prior to
use. Acetone and diethyl ether were dried over activated
Before the report, the copolymers of ethylene with polar
monomers have low weight average molecular weight about
1.0 9 104 g/mol. Guan et al. [19] and Ye et al. [20] adopted
Pd-diimine catalysts to catalyze the copolymerization of
ethylene and acrylic monomers, comonomer insertion rate
was 2.0 and 3.6 mol%, respectively. Nevertheless, the cat-
alytic activities were relatively low, about 1.6 9
102 g/(molPd.h) and 9.2 9 102 g/(molPd.h), respectively.
Pugh et al. [21] investigated that [P, O]-type palladium
complexes catalyzed copolymerization of ethylene with
acrylic ester and the comonomer incorporation rate was up
˚
Davison 5 A molecular sieves prior to use.
123

Copolymers of Ethylene and Vinyl Amino Acidic Ester with High Molecular Weight Prepared by…
2.2 Characterization
remaining viscous oil was dissolved in a mixture of
aqueous 5 % NaOH/Et2O (200 mL). The organic layer was
collected, dried with MgSO4 and concentrated. The resul-
tant viscous oil was washed with 200 mL of hexane,
50 mL at a time, and purified by vacuum. Yellow liquid
was obtained with yield of 31 %. 1H NMR(600 MHz,
CDCl3): d 6.99 (d, 2H, benzene), d 6.81 (d, 2H, benzene), d
5.90 (m,1H, CH=CH2), d 5.83 (d, 1H, NH–CH), d
4.97–5.00 (d, 2H, –CH2–CH=CH2), d 4.82 (q, 1H, CH–
NH), d 4.18 (q, 2H, CH2–CH3), d 3.93 (t, 2H, CH2–O), d
3.06 (d, 2H, CH2=CH), d 2.12 (m, 2H, CH2–CH), d 1.99 (s,
3H, CH3–C), d 1.8 (m, 2H, CH2–CH2), d 1.6 (m, 2H, CH2–
CH2), d 1.3 (t, 3H, CH3–CH2); FT-IR (cm-1, KBr): 3365
(N–H), 1722 (C=O), 1657 (C–N), 1513 (N–H). Anal.
Calc.(%) for C19H27NO4 (333.42 g/mol): C, 68.47; H,
8.11; N, 4.20. Found: C, 68.56; H, 8.03; N, 4.25. ESI–MS
m/z calculated for [M?H]?. C19H28NO4: 334.42 found
334.31.
1H NMR spectra were recorded on a Varian INOVA
600 MHz spectrometer in deuterated chloroform (CDCl3)
solution at 25 °C and tetramethylsilane (TMS) was used as
reference. Elemental analyses were performed on a Perkin
Elmer 2400 microanalyzer, using combustion method with
quantitative oxygen with thermal conductivity detector.
Fourier transform infrared (FT-IR) spectra were recorded
on a Nicolet 5DXC FT-IR spectrograph. The spectra were
obtained at 40 cm-1 resolution, and average data were
obtained from at least 32 scans in the standard wavenumber
range from 500 to 4000 cm-1. Mass spectrum was recor-
ded by Esquire-LC mass spectroscopy, acetone as dissol-
vent. 13C NMR spectra were obtained on a Varian INOVA
500 MHz (125 MHz for 13C NMR) instrument. The con-
ditions used for quantitative 13C NMR were a copolymer
content up to 15 wt% in solution, using ortho-dichlor-
obezene (d4) as the solvent at 125 °C, tetramethylsilane
(TMS) as internal reference. The molecular weight and
molecular weight distribution (MWD) were measured with
a PL-GPC 200 instrument, using standard polyethylene
(PE) as reference and 1,2,4-trichlorobenzene as solvent at
150 °C. DSC thermograms were recorded with a PA5000-
2.5 Synthesis of Catalyst Precursors
Aniline (1.5 mL, 16.2 mmol) was treated with an equiv. of
CH3MgCl for 3 h in toluene (80 mL), then
chlorodiphenylphosphine (3 mL, 16.2 mmol) was injected
with a syringe. The mixture was stirred for 5 h at room
temperature. Subsequently, the solvent was removed in
vacuo and the residual was dissolved by hexane (50 mL).
The solution was concentrated and put in a refrigerator at
-10 °C. White crystal with a yield of 70.2 % was
obtained. 2, 4, 6-trifluoroaniline was treated with an equiv.
of CH3MgCl for 3 h in toluene, then dichlorodimethylsi-
lane (2 mL, 16.2 mmol) was injected. The mixture was
stirred for 5 h at room temperature. Subsequently, the
solvent was removed in vacuo and the residual was dis-
solved by hexane. The solvent was removed in vacuo.
Light yellow liquid with a yield of 83.0 % was obtained.
Diphenylphosphone-aniline (3.15 g, 11.4 mmol) was trea-
ted with an equiv. of CH3MgCl for 3 h in toluene, then
(2.72 g, 11.4 mmol) chlorodimethyisilane-(2, 4, 6-trifluo-
roaniline) was added. The mixture was stirred for 5 h at
room temperature. Subsequently, the solvent was removed
in vacuo and the residual was dissolved in hexane. The
solution was concentrated and put in a refrigerator at
-10 °C. White crystal (Ligand 1 (L1)) was obtained
(1.03 g, 18.8 %; Scheme 1). L1 (C26H24N2SiPF3, Fw =
480): 1H NMR (DMSO-d6), d 0.14 (s, 6H, methyl), d 4.0 (s,
1H, N–H), d 6.20 (s, 2H, benzene), d 6.46-7.01 (m, 5H,
benzene); d 7.22–7.46 (m, 10H, benzene). Element analysis
calculated (%): C, 64.98; H, 5.00; N, 5.83; found: C, 65.06;
H, 4.98; N, 5.80. FT-IR (cm-1, KBr): 3274 (N–H). ESI–
MS m/z calculated for [M?H]?. C26H25N2SiPF3: 481.02
found 481.12 Scheme 1).
DSC instrument at a rate of 10 K min-1
.
2.3 Polymerization Procedure
All polymerization manipulations were carried out in a
flamed 300 mL Schlenk-type glassware on a dual-manifold
Schlenk line. Freshly distilled toluene (80 mL), the desired
amount of catalysts (Cat.1-Cat.9) and MAO were intro-
duced into the glassware. The mixture was stirred for
15 min for preactivation. A desired amount of N-acetyl-O-
(hex-5-enyl)-L-tyrosine ethyl ester dissolved in toluene was
treated by an equivalent of AlEt3 for the desired time
before it was injected into the Schlenk flask. Pressure of
ethylene in feed was 0.2 MPa and the reactor was rapidly
heated to the desired temperature. The polymerization
maintained for 10 min. The reaction was terminated with
10 wt% HCl in alcohol. The obtained product was filtered,
washed, dried to constant weight in a vacuum oven at
80 °C, then weighted and the catalytic activity was
calculated.
2.4 Synthesis of N-acetyl-O-(hex-5-enyl)-L-tyrosine
Ethyl Ester
N-acetyl-L-tyrosine ethyl ester (5 g, 18.6 mmol) in acetone
(80 mL), K2CO3 (3.7 g, 26.8 mmol) and 6-bromo-1-hex-
ene (2.5 mL, 18.6 mmol) were added to Schlenk-type
glassware in order. The mixture was stirred at reflux for
2 days. Then the solvent was removed in vacuo, and the
123

J. Wang et al.
R
R
Cl
Si
CH3
NH2
+
Cl
R
NH2
+
P
Cl
CH3
CH3MgCl
CH3MgCl
R
R
Cl
Si
R
NH
CH3
NH
P
+
CH3
CH3MgCl
Toluene, 50oC,4h
MCl4
N
P
N
P
H3C
H3C
Si
Cl
Si
M
NH
Cl
H3C
N
H3C
R
Cl
R
R
R
R
R
R = F, CH3, H; M = Ti, Zr, Hf
Scheme 1 Synthesis of the non-metallocene catalysts
The ligand 2 (L2) derived from 2, 4, 6-trimethylaniline
and the ligand 3 (L3) from aniline. L2 (C29H33N2SiP,
(N–H). ESI–MS m/z calculated for [M ? Na]?. C26H27
N2SiPNa: 449.32 found 449.25.
1
Fw = 468): H NMR (DMSO-d6), d 0.15 (s, 6H, methyl),
L1 Ti complex (Cat.1) was prepared by the treatment of
L1 (0.48 g, 1.0 mmol) with TiCl4 (0.11 mL, 1.0 mmol)
Æ
adding by syringe into toluene 50 mL at 0 C. The reaction
d 2.36 (s, 9H, methyl on benzene), d 4.3 (s, 1H, N–H), d
6.36 (s, 2H, benzene), d 6.43–7.12 (m, 5H, benzene); d
7.12-7.43 (m, 10H, benzene). Element analysis calculated
(%): C, 64.98; H, 5.00; N, 5.83; found: C, 65.07; H, 4.92;
N, 5.88. FT-IR (cm-1, KBr): 3289 (N–H). ESI–MS m/z
calculated for [M ? H]?. C29H34N2SiP: 469.56 found
469.42.
was lasted for 6 h at 40 °C. The mixture was filtered. After
washing for four times and then drying, a light brown
powder (Cat.1) was obtained (0.63 g, 85.1 %; Scheme 1)
and further characterized. Cat.1 was confirmed by 1H (13C,
29Si, 31P, 19F) NMR, MS and elemental microanalysis.
Cat.1 (C26H23N2SiPF3TiCl3, Fw = 634): 1H NMR
(DMSO-d6): d 0.16 (s, 6H, methyl), d 6.23 (s, 2H, ben-
zene), d 6.46-7.04 (m, 5H, benzene), d 7.22-7.42 (m, 10H,
benzene). 13C NMR (DMSO-d6): d 1.1 (Si(CH3)2), d 1.2
(Si(CH3)2), d 98.9 (Ar–C), d 113.6 (C–N), d 115.1 (Ar–C),
1
L3 (C26H27N2SiP, Fw = 426): H NMR (DMSO-d6), d
0.14 (s, 6H, methyl), d 4.2 (s, 1H, N–H), d 6.42-7.00 (m,
10H, benzene); d 7.28–7.61 (m, 10H, benzene). Element
analysis calculated (%): C, 64.98; H, 5.00; N, 5.83; found:
C, 65.01; H, 4.98; N, 5.85. FT-IR (cm-1, KBr): 3305
123

Copolymers of Ethylene and Vinyl Amino Acidic Ester with High Molecular Weight Prepared by…
Catalyst
calculated (%): C 50.24, H 3.70, N 4.51; found C 50.27, H
3.72, N 4.48. ESI–MS m/z calculated for [M?Na]?. C26-
H23N2SiPF3HfCl3Na: 787.64 found 787.59.
+
y
x
x
y
L2 Ti complex (Cat.4) (C29H32N2SiPTiCl3, Fw = 622):
1H NMR (DMSO-d6): d 0.15 (s, 6H, methyl), d 2.36(s, 9H,
methyl on benzene), d 6.38 (s, 1H, benzene), d 6.46–7.02
(m,7H, benzene), d 7.22–7.41(m, 10H, benzene). 13C NMR
(DMSO-d6): d 1.1 (Si(CH3)2), d 1.2 (Si(CH3)2), d 12.8
(C(CH3)), d 21.6 (C(CH3)), d 25.8 (C(CH3)), d 115.1 (Ar–
C), d 118.5 (Ar–C), d 121.5 (C(CH3)), d 125.8 (C(CH3)), d
127.8 (Ar–C), d 129.5 (Ar–C), d 130.1 (Ar–C), d 141.8 (C–
N), d 146.6 (C–N). 19P NMR (DMSO-d6): d 49.98. 29Si
NMR (DMSO-d6): d -9.82. Element analysis calculated
(%): C 55.35, H 4.94, N 4.61; found C 55.39, H 4.91, N
4.63. ESI–MS m/z calculated for [M?Na]?. C29H32N2
SiPTiCl3Na: 645.43 found 645.38.
O
O
O
O
NH
NH
O
O
O
O
L2 Zr complex (Cat.5) (C29H32N2SiPZrCl3, Fw = 665):
1H NMR (DMSO-d6): d 0.15 (s, 6H, methyl), d 2.35 (s, 9H,
methyl on benzene), d 6.38 (s, 1H, benzene), d 6.43-7.02
(m, 7H, benzene), d 7.22–7.37(m, 10H, benzene). 13C
NMR (DMSO-d6): d 1.1 (Si(CH3)2), d 1.2 (Si(CH3)2), d
12.7 (C(CH3)), d 21.3 (C(CH3)), d 25.9 (C(CH3)), d 115.2
(Ar–C), d 118.7 (Ar–C), d 121.6 (C(CH3)), d 125.3
(C(CH3)), d 127.6 (Ar–C), d 129.3 (Ar–C), d 129.9 (Ar–C),
d 141.6 (C–N), d 146.3 (C–N). 19P NMR (DMSO-d6): d
49.45. 29Si NMR (DMSO-d6): d -9.67. Element analysis
calculated (%): C 54.90, H 4.90, N 4.58; found C 54.87, H
4.89, N 4.61. ESI–MS m/z calculated for [M?H]?. C29
H32N2SiPZrCl3: 666.57 found 666.58.
Scheme 2 Copolymerization of ethylene and N-acetyl-O-(hex-5-
enyl)-L-tyrosine ethyl ester
d 118.6 (Ar–C), d 129.5 (Ar–C), d 130.1 (Ar–C), d 149.1
(C-F), d 153.8 (C–F). 19F NMR (DMSO-d6): d -122.20,
-129.01. 31P NMR (DMSO-d6): d 42.86. 29Si NMR
(DMSO-d6): d -10.20. Element analysis calculated (%): C
49.21, H 3.63, N 4.42; found C 49.19, H 3.61, N 4.45. ESI–
MS m/z calculated for [M?H]?.C26H24N2SiPF3TiCl3:
635.82 found 635.77.
L2 Hf complex (Cat.6) (C29H32N2SiPHfCl3, Fw = 752):
1H NMR (DMSO-d6): d 0.14 (s, 6H, methyl), d 2.35 (s, 9H,
methyl on benzene), d 6.38 (s, 1H, benzene), d 6.46-7.02 (m,
7H, benzene), d 7.22–7.37 (m, 10H, benzene). 13C NMR
(DMSO-d6): d 1.1 (Si(CH3)2), d 1.2 (Si(CH3)2), d 12.9
(C(CH3)), d 21.5 (C(CH3)), d 25.7 (C(CH3)), d 114.8 (Ar–C),
d 118.6 (Ar–C), d 121.7 (C(CH3)), d 125.6 (C(CH3)), d 127.5
(Ar–C), d 129.6 (Ar–C), d 130.3 (Ar–C), d 141.7 (C–N), d
146.9 (C–N). 19P NMR (DMSO-d6): d 49.72. 29Si NMR
(DMSO-d6): d -9.51. Element analysis calculated (%): C
56.57, H 5.05, N 4.71; found C 56.56, H 5.03, N 4.75. ESI–
MS m/z calculated for [M?H]?. C29H33N2SiPHfCl3: 753.25
found 753.21.
Cat.2-9 were synthesized and confirmed according to the
method mentioned above. L1 Zr complex (Cat.2) (C26H23
N2SiPF3ZrCl3, Fw = 677): 1H NMR (DMSO-d6): d 0.15 (s,
6H, methyl),d 6.21 (s, 2H, benzene), d 6.46-7.02 (m, 5H,
benzene), d 7.22–7.38 (m, 10H, benzene). 13C NMR
(DMSO-d6): d 1.1 (Si(CH3)2), d 1.2 (Si(CH3)2), d 98.7 (Ar–
C), d 113.5 (C–N), d 115.2 (Ar–C), d 118.7 (Ar–C), d 129.5
(Ar–C), d 130.0 (Ar–C), d 149.2 (C–F), d 153.6 (C–F). 19
F
NMR (DMSO-d6): d -122.32, -129.43. 31P NMR (DMSO-
d6): d 43.03. 29Si NMR (DMSO-d6): d -10.32. Element
analysis calculated (%): C 48.83, H 3.60, N 4.38; found C
48.81, H 3.64, N 3.57. ESI–MS m/z calculated for [M?H]?.
C26H23N2SiPF3ZrCl3: 678.39 found 678.31.
L3 Ti complex (Cat.7) (C26H26N2SiPTiCl3, Fw = 580):
1H NMR (DMSO-d6): d 0.15 (s, 6H, methyl), d 6.41–7.02 (m,
10H, benzene), d 7.22–7.53(m, 10H, benzene). 13C NMR
(DMSO-d6): d 1.1 (Si(CH3)2), d 1.2 (Si(CH3)2), d 112.4 (Ar–
C), d 115.1 (Ar–C), d 117.2 (Ar–C), d 118.1 (Ar–C), d 129.7
(Ar–C), d 130.0 (Ar–C), d 143.3 (C–N), d 146.5 (C–N). 19P
NMR (DMSO-d6): d 49.40. 29Si NMR (DMSO-d6): d -9.55.
Element analysis calculated (%): C 53.89, H 4.49, N 4.84;
found C 53.87, H 4.51, N 4.82. ESI–MS m/z calculated for
[M?H]?. C26H27N2SiPTiCl3:581.31 found 581.34.
L1 Hf complex (Cat.3) (C26H23N2SiPF3ZrCl3,
1
Fw = 677): H NMR (DMSO-d6): d 0.15 (s, 6H, methyl),
d 6.25 (s, 2H, benzene), d 6.46–7.03 (m, 5H, benzene), d
7.22–7.41 (m, 10H, benzene). 13C NMR (DMSO-d6): d 1.1
(Si(CH3)2), d 1.2 (Si(CH3)2), d 98.8 (Ar–C), d 113.2 (C–
N), d 115.0 (Ar–C), d 118.9 (Ar–C), d 129.2 (Ar–C), d
130.3 (Ar–C), d 149.3 (C–F), d 153.7 (C–F). 19F NMR
(DMSO-d6): d -122.24, -129.32. 31P NMR (DMSO-d6): d
42.98. 29Si NMR (DMSO-d6): d -10.41. Element analysis
123

J. Wang et al.
L3 Zr complex (Cat.8) (C26H26N2SiPZrCl3, Fw = 623):
1H NMR (DMSO-d6): d 0.14 (s, 6H, methyl), d 6.43–7.05
(m, 10H, benzene), d 7.22–7.53(m, 10H, benzene). 13C
NMR (DMSO-d6): d 1.1 (Si(CH3)2), d 1.2 (Si(CH3)2), d
112.1 (Ar–C), d 115.3 (Ar–C), d 117.1 (Ar–C), d 118.3
(Ar–C), d 129.6 (Ar–C), d 130.0 (Ar–C), d 143.4 (C–N), d
146.6 (C–N). 19P NMR (DMSO-d6): d 49.36. 29Si NMR
(DMSO-d6): d -9.61. Element analysis calculated (%): C
53.33, H 4.44, N 4.79; found C 53.34, H 4.45, N 4.81. ESI–
MS m/z calculated for [M?Na]?. C26H26N2SiPZrCl3Na:
646.69 found 646.65.
Cat.6 with L2; Cat.7, Cat.8 and Cat.9 with L3 showed the
similar polymerization behavior for homopolymerization
of ethylene and copolymerization of ethylene with
N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester. We can
also notice that the structure of the ligands and the center
metal atoms of these catalysts influenced the ethylene (co)
polymerization behavior. Cat.1 to Cat.3 were used for both
homopolymerization of ethylene and copolymerization of
ethylene with N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl
ester. The MWs were ranged from 8.65 9 105 to
6.42 9 105 g/mol for polyethylene, from 2.56 9 105 to
1.41 9 105 g/mol for copolymer of ethylene with
N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester. The MWDs
were slightly broadened from 1.75 to 1.86 for polyethylene
and from 2.76 to 2.87 for the copolymers. This result
implied that the chain transfer for the copolymerization
took place in some extent, compared to the homopoly-
merization of ethylene.
L3 Hf complex (Cat.9) (C26H26N2SiPHfCl3,
1
Fw = 710): H NMR (DMSO-d6): d 0.13 (s, 6H, methyl),
d 6.41-7.05 (m, 10H, benzene), d 7.22–7.52 (m, 10H,
benzene). 13C NMR (DMSO-d6): d 1.1 (Si(CH3)2), d 1.2
(Si(CH3)2), d 112.1 (Ar–C), d 115.2 (Ar–C), d 117.2 (Ar–
C), d 118.4 (Ar–C), d 129.6 (Ar–C), d 130.2 (Ar–C), d
143.6 (C–N), d 146.8 (C–N). 19P NMR (DMSO-d6): d
49.39. 29Si NMR (DMSO-d6): d -9.63. Element analysis
calculated (%): C 55.03, H 4.59, N 4.94; found C 55.04, H
4.63, N 4.92. ESI–MS m/z calculated for [M?H]?. C26
H27N2SiPHfCl3: 711.62 found 711.58.
From the 13C NMR results mentioned above, the com-
plexes from the same ligand (L1, L2 or L3) complexed
with different transition metals (Ti, Zr and Hf) showed
almost identical chemical shifts, which indicated that the
transition metals did coordinate with the heteroatoms, not
with the carbon atoms of these ligands. A lot of work was
done for single crystal, unfortunately, there was no one
good enough for X-ray analysis.
It was obvious that Cat.1 to Cat.3 with L1 exhibited the
highest catalytic activity (Runs 1 to 6 in Table 1), com-
pared with other catalysts with the same transition metals.
This depended on the electric and steric effect of ligands.
Compared with L1, L2 with methyl on benzene ring had
large steric block. Methyl on para-position of L2 had
strong electron donating effect that led to high electron
density around the active center. It hindered the coming
monomer from approaching to metal atom.
As shown in Table 1, the catalyst with fluorine atom on
para-position of aniline showed higher activity than that
with methyl group, it was due to that fluorine atom on para-
position of aniline would decrease the electron cloud
density of metal center, attracting ethylene move to the
active center. The catalysts include a large five-membered
ring, making sure the stability of the active centers.
The effects of polymerization conditions on copoly-
merization of ethylene with N-acetyl-O-(hex-5-enyl)-L-ty-
rosine ethyl ester catalyzed by Cat.2 were investigated:
temperature, Al/Zr ratio in mol, comonomer concentration
and catalysts concentration. The results were listed in
Table 2.
3 Results and Discussion
The obtained [N, Si, N, P] non-metallolene catalysts
(Cat.1–9) were utilized for ethylene (co)polymerization,
MAO used as cocatalyst (Scheme 2). The effects of centre
metal atoms (Ti, Zr and Hf) and the structure of catalyst
ligands on ethylene (co-) polymerization were investigated,
and the data were compiled in Table 1.
From Table 1, the results indicated that these catalysts
were favorable for both homopolymerization of ethylene
and copolymerization of ethylene with N-acetyl-O-(hex-5-
enyl)-L-tyrosine ethyl ester with high catalytic activity. The
highest catalytic activity for homopolymerization of ethy-
lene was up to 1.66 9 106 gPE (mol Zr)-1.h-1 and that of
copolymerization of ethylene with N-acetyl-O-(hex-5-
enyl)-L-tyrosine ethyl ester was up to 6.24 9 104 gP (mol
Zr)-1.h-1 catalyzed by Cat. 2. The catalyst with zirconium
as center metal showed the higher catalytic activity for
ethylene (co)polymerization. However, the polymer
obtained by catalyst with hafnium as metal center had the
highest weight average molecular weight. Cat.4, Cat.5 and
From Table 2, we can notice that Cat.2 featured rather
high tolerance to the reaction conditions and exhibited
highest catalytic activity of 6.56 9 104 g P (mol-1 Zr-1
h-1) (run 20 in Table 2) at 50 °C for the copolymerization
of ethylene with N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl
ester. With an increase of reaction temperature from 25 to
70 °C, the MW of the obtained copolymers decreased
gradually and MWDs became broader slightly. It is pos-
sible that the weight–average MW of the obtained
copolymers is determined by Kp/Ktr ratio. With the
increasing of the polymerization temperature, Ktr increases
faster than Kp. Therefore, rate of chain transfer to mono-
mers and MAO enhances much more than propagation
123

Copolymers of Ethylene and Vinyl Amino Acidic Ester with High Molecular Weight Prepared by…
Table 1 Effects of the metal
Run
Catalysts
Aa (910-4
)
N-contb (wt%)
Mwc(910-5
)
Mw/Mcn
Tdm (°C)
atoms and the structure of
catalyst ligands on ethylene (co-
) polymerization
1
2e
Cat.1 (Ti, L1)
145
2.35
166
6.24
133
4.13
107
2.03
119
5.53
101
3.86
94.4
1.52
125
3.78
107
2.13
–
6.42
1.41
8.23
1.65
8.65
2.70
7.21
1.32
7.63
1.43
8.17
2.56
7.38
1.27
7.52
1.48
7.92
2.54
1.81
2.87
1.75
2.76
1.86
2.85
1.79
2.89
1.93
3.06
1.78
3.08
2.47
2.76
1.81
2.96
1.93
3.03
134.5
135.8
134.2
137.2
134.5
138.1
134.5
135.3
134.2
136.3
134.4
137.7
134.8
135.1
134.7
134.8
134.6
137.9
9.25
–
3
Cat.2 (Zr, L1)
Cat.3 (Hf, L1)
Cat.4 (Ti, L2)
Cat.5 (Zr, L2)
Cat.6 (Hf, L2)
Cat.7 (Ti, L3)
Cat.8 (Zr, L3)
Cat.9 (Hf, L3)
4e
5
6e
22.42
–
13.00
–
7
8e
9
10e
5.75
–
17.56
–
11
e
12
9.45
–
13
14e
3.79
–
15
16e
17
13.36
–
18e
1.06
Reaction conditions: pressure of ethylene, 0.2 9 106 Pa; catalyst concentration, 2.0 9 10-4 mol L-1
Al/M in mol, 600; reaction temperature, 60 °C; solvent, toluene, 80 mL; polymerization time, 10 min
;
a
Catalytic activity, gPE/(molM.h)
Incorporation content of N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester, determined by 13C NMR
b
c
Determined by GPC
d
Determined by DSC
e
Comonomer: 10 g/L
Table 2 Effects of polymerization conditions on copolymerization of ethylene with N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester catalyzed by
Cat.2
Run
Ta (°C)
Cb (9104)
Comonc (g/L)
Al/Zrd
Ae (910-4
)
Mfw (910-5
)
Mw/Mfn
Tgm (°C)
N-Conth (wt%)
19
20
21
22
23
24
25
26
27
28
29
25
50
70
50
50
50
50
50
50
50
50
2.0
2.0
2.0
1.0
5.0
2.0
2.0
2.0
2.0
3.0
4.0
10
10
10
10
10
5
600
600
600
600
600
600
600
300
1000
600
600
4.63
6.56
4.93
3.84
4.96
6.52
5.23
2.32
3.03
6.07
5.54
3.79
2.67
2.11
2.76
2.16
2.66
2.33
1.76
0.93
2.58
2.32
2.78
2.82
3.13
3.01
3.25
2.83
3.07
2.98
3.57
3.09
3.18
137.9
138.6
138.4
135.8
137.5
137.2
138.7
137.8
138.0
138.1
137.8
19.61
22.40
21.57
9.94
14.54
13.63
23.07
18.64
20.64
20.17
18.39
20
10
10
10
10
Reaction conditions: pressure of ethylene, 0.2 9 106 Pa; dissolvent, toluene, 100 mL; polymerization time, 10 min
a
Reaction temperature
b
Catalyst concentration
c
Comonomer, N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester in feed
d
Al/Zr in mol
Activity of catalysts, g PE(mol-1 Zr-1 h-1
e
)
f
Results of GPC
g
h
Results of DSC
Incorporation content of 1-octene, results of 13C NMR
123

J. Wang et al.
reaction. [25] The incorporation rate of N-acetyl-O-(hex-5-
enyl)-L-tyrosine ethyl ester was changed slightly at differ-
ent temperature.
time, it is more difficult for the monomers approaching to
the active centers. Therefore, polymer chain can be snarled
easily, resulting in the chain propagation rate decreasing.
Furthermore, catalyst concentration influenced the incor-
poration rate of N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl
ester slightly.
As shown in Table 2, when catalyst concentration was
2.0 9 10-4 g/L, catalytic activity exhibited the highest
value of 6.56 9 104 g PE(mol-1 Zr-1 h-1). With catalyst
concentration increased from 1.0 9 10-4 to 2.0 9 10-4 g/
L, catalytic activity increasing from 3.84 9 104 g PE
(mol-1 Zr-1 h-1) to 6.56 9 104 g PE (mol-1 Zr-1 h-1).
However, when catalyst concentration increased from
2.0 9 10-4 to 5.0 9 10-4 g/L, catalytic activity
decreased. Because the active centers of the catalysts were
devitalized by impurity easily, when catalyst concentration
was 1.0 9 10-4 g/L, the number of activity species was
less. But too high catalyst concentration leads to fast
polymer chain aggregation within the same polymerization
The concentration of N-acetyl-O-(hex-5-enyl)-L-ty-
rosine ethyl ester in feed influenced the incorporation
content of N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester.
For example, when the concentration of N-acetyl-O-(hex-
5-enyl)-L-tyrosine ethyl ester was 5 g/L in the reaction
system, the insertion content of the comonomer was
13.63 wt%; while the concentration increased to 10 g/L,
the insertion content of the comonomer increased to
22.40 wt%. However, keeping on increasing the concen-
tration to 20 g/L, the insertion content of the comonomer
slightly raised to 23.07 wt% (runs 24, 20 and 25 in
Table 2). The results indicated that there was a limit to
amount of the comonomer in feed. When it’s enough for
the polymerization, the extra comonomer would not work
anymore. The MWDs of copolymers was about 3.0, indi-
cating that the polymerization behavior followed single-
metal mechanism.
The catalytic activity was influenced by Al/Zr molar
ratio strongly. When Al/Zr molar ratio in mol was 600,
catalytic activity of the copolymerization of ethylene with
N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester reached the
maximum value of 6.56 9 104 gP/(molZr.h). As Al/Zr
molar ratio ranged from 300 to 600, catalytic activity
increased from 2.32 9 104 to 6.56 9 104 gP/(molZr.h)
(runs 26, and 20 in Table 2). However, catalytic activity
decreased with further increasing Al/Zr molar ratio. It is
possible that both the reaction system purifying and the
chain transfer reaction to MAO consume amount of MAO.
However, Trimethylaluminum in MAO can reduce oxida-
tion state of Ti(IV) to Ti(III), but only Ti(IV) is favorable
for a-olefin polymerization. In addition, MAO influenced
MWs and MWDs of copolymers. Part of active species was
transferred to b-H with less MAO, which led to lower
activity, lower MWs, and broader MWDs. However, much
MAO made chain transfer to MAO easy, resulting in lower
MWs and broader MWDs (run 27 in Table 2). Hence, the
active center can be stable and chain transfer to b-H and
MAO be controlled only when the proper amount of MAO
is introduced. The incorporation rate of N-acetyl-O-(hex-5-
enyl)-L-tyrosine ethyl ester was influenced by Al/Zr molar
ratio slightly, implying that Al/Zr molar ratio did not the
main factor of influencing comonomer incorporation.
The high temperature liquid 13C NMR spectra of ethy-
lene/N-acetyl-O-(hex-5-enyl)-L-tyrosine
ethyl
ester
copolymer promoted by Cat.2 was presented in Fig. 1a.
One broad signal at d = 23.6–35.5 ppm represented
methylene. The signals at d = 172.32 and 169.46 ppm
Fig. 1 High temperature liquid 13C NMR spectra of ethylene/N-
acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester copolymer from run 20 in
Table 2
123

Copolymers of Ethylene and Vinyl Amino Acidic Ester with High Molecular Weight Prepared by…
were attributed to the carbon atoms (Ca and Cb) from the
amino group and the ester group, respectively. The signals
at d = 155.61, 131.83 and 60.06 ppm were attributed to
the carbon atoms (Ce, Cd and Cc), however, the signal at
d = 131.83 ppm was overlaped with the signals of the
solvent, ortho-dichlorobezene (d4). It indicated that the
comonomer had been inserted into the polyethylene chain.
There are two main patterns of chain transfer in the
copolymerization process catalyzed by non-metallocene
catalyst [25]: The first is that b-H transfers to active center
and monomer; the second is that the growing chain trans-
fers to MAO. The former produces the polymer with
unsaturated end group, while the latter obtains the polymer
with saturated end group. Chain termination reaction of
olefin polymerization catalyzed by non-metallocene cata-
lyst can also get polymer with saturated end group. From
Fig. 1b, we can see that there was no signal that repre-
sented the unsaturated carbon–carbon double bond, but a
signal at d 14–15 ppm assigned to methyl was observed.
This implied that the obtained copolymer of ethylene with
N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester, catalyzed
by the catalyst system of Cat.2/MAO, was featured methyl
group at the chain end. The result confirmed that the chain
transfer to MAO was the dominant pattern.
reactivity rates of ethylene and N-acetyl-O-(hex-5-enyl)-
L-tyrosine ethyl ester were 152.99 and 0.045, respectively.
The average sequence lengths for ethylene units and the
comonomer units were 34.52 and 1.03, respectively.
Moreover, no continuous fragment of N-acetyl-O-(hex-5-
enyl)-L-tyrosine ethyl ester was found within the copoly-
mer chain ([NNN] = 0). So we can infer that N-acetyl-O-
(hex-5-enyl)-L-tyrosine ethyl ester was single dispersed
into the polyethylene chain, which can provide the
copolymer a good potential application value.
The FT-IR plots of the obtained copolymers were per-
formed (Fig. 2). Signals at 2918, 2849, 1470 and 718 cm-1
are characteristic signals to linear polyethylene. The signal
at 718 cm-1 represents the long chain units [(CH2)n, n [ 4]
of methylene. The signals at 2918, 2849 and 1470 cm-1
are C–H stretching vibration absorption and bending
vibration absorption peaks. There was an evident band at
1738 cm-1 (Fig. 4d) which was C=O vibration absorption
of the saturated ester from the branched group. Compared
Table 4 The content of different sequences on copolymer and
reactivity ratio of monomer
[ENE]
[ENN]
0.002
[NNN]
[NEN]
0.053
[EEN]
0.326
[EEE]
95.095
4.524
0
Different carbon atoms between 10 and 40 ppm were
assigned in Table 3. According to the area integral of each
carbon atom, Randall [30] method was used to calculate
the content of different sequence structure, and then cal-
culated the comonomer insertion rate as well as reactivity
ratio and average sequence length of the two monomers.
The results were shown in Table 4. The calculation results
showed that the comonomer insertion rate was 22.40 wt%
within the copolymer chain catalyzed by Cat.2. The
Sample
Mole fractions
Reactivity
ratio
The average
sequence
length
[E]
[N]
rE
rN
nE
nN
Run 4 in Table 2 0.9763 0.0237 152.99 0.045 34.52 1.03
E polyethylene,
ester)
N poly(N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl
Table 3 13C NMR data of
Peak no.
Carbon type
Monomer sequence
Chemical shift
Calculated
carbon atoms on the copolymer
of ethylene and N-acetyl-O-
(hex-5-enyl)-L-tyrosine ethyl
ester
Found
1
CH
ad??CH2(6)
ENE
38.13
34.90
35.00
34.54
32.31
30.47
29.98
29.51
27.28
27.29
26.89
23.36
14.12
37.95
35.35
35.17
34.63
31.64
30.45
29.44
29.17
27.24
27.18
27.16
22.97
14.03
2
NNEE?NNE
ENEN
3
ac
4
ad??CH2(6)
CH2(3)
cd?
ENEE?ENE
ENE ? NNE ? NNN
NEEE
5
6
7
d?d?
(EEE)n
8
CH2(3)
CH2(5)
bd?
ENE
9
ENE?NNE?NNN
ENEE
10
11
12
13
bd?
ENEE
CH2(2)
CH3
ENE?NNE?NNN
ENE?NNE?NNN
E polyethylene, N Poly(N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester)
123

J. Wang et al.
Fig. 3 DSC spectrums (the second heating) of ethylene homopoly-
mer (A, run 1 in Table 1) and ethylene/N-acetyl-O-(hex-5-enyl)-
L-tyrosine ethyl ester copolymers (B, run 22; C, run 24; D, run 20 in
Table 2)
Fig. 2 FT-IR spectrums of ethylene homopolymer (A, run 1 in
Table 1) and ethylene/N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester
copolymer (B, run 20; C, run 22; D, run 24 in Table 2)
to C=O vibration absorption of N-acetyl-O-(hex-5-enyl)-L-
tyrosine ethyl ester at 1760 cm-1 [31], the bands of C=O of
the copolymer B moved toward red area and its vibration
absorption wave number became 1738 cm-1, which con-
tributed to the forming of hydrogen bonds among inter- and
intra- of the copolymer chains [32]. Band at 1259 cm-1
corresponded to C-O vibration absorption. Stretching
vibration absorption and bending vibration absorption of
C-O on ester group were shown at 1094 and 1023 cm-1
.
Band at 1655 cm-1 corresponded to C=O vibration
absorption of amide group. Band at 802 cm-1 represented
the vibration absorption of substituted benzene. The results
indicated that the comonomer N-acetyl-O-(hex-5-enyl)-L-
tyrosine ethyl ester had incorporated into the copolymer
chains.
Fig. 4 GPC curves of ethylene homopolymer (A, run 1 in Table 1)
and ethylene/N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester copoly-
mers (B, run 22; C, run 20; D, run 24 in Table 2)
As shown in Fig. 3, the melting points of polymers (A,
B, C, D) increase in order from 134.5 to 138.6 °C, with the
increase of comonomer insertion rate. It can be contributed
to the hydrogen bonding interaction between the branch
chains. Melting enthalpy of polyethylene (A) was 198.6 J/g
and crystallinity was 69.1 % which was calculated from
area integration. However, the melting enthalpy of the
copolymers (B, C, D) was 159.2, 153.7 and 148.8 J/g,
respectively. Using the same method, we figured out that
the crystallinity of the copolymers (B, C, D) were 55.4,
53.5 and 51.8 %, respectively. Reducing crystallinity was
ascribed to the insertion of N-acetyl-O-(hex-5-enyl)-L-ty-
rosine ethyl ester, which destroyed the regularity of poly-
mer chain. The higher comonomer insertion rate was, the
lower crystallinity became.
The GPC curves of ethylene homopolymer and
copolymers (Fig. 4) were monomodal and symmetric in
shape, meaning that these copolymers were not a mixture
of PE homopolymer and small amount of oligomers con-
taining comonomer. GPC results exhibited that MWs of
ethylene homopolymer (Fig. 4a) and copolymers (Fig. 4b–
d)
were
6.42 9 105,
2.76 9 105,
2.66 9 105,
2.67 9 105 g/mol, respectively. MWs of the copolymers
were lower than that of the homopolymer, however,
MWDs of the copolymers were broader, which indicated
that the chain transfer took place during the copolymer-
ization when N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl
ester was added into the polymerization system. MWD of
123

Copolymers of Ethylene and Vinyl Amino Acidic Ester with High Molecular Weight Prepared by…
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The copolymers of ethylene and N-acetyl-O-(hex-5-enyl)-
L-tyrosine ethyl ester were synthesized by [N, Si, N, P]-
type non-metallocene catalysts, MAO used as cocatalyst.
Cat.2 showed the highest catalytic activity of 6.56 9 104 g/
(molZr.h) for the copolymerization under the optimal
reaction conditions: polymerization temperature of 50 °C,
Al/Zr molar ratio of 600, catalyst concentration of
2.0 9 10-4 mol/L, the amount of comonomer in feed of
10 g/L, polymerization time of 10 min and toluene as
dissolvent. The highest comonomer incorporation rate was
22.40 wt% determined by 13C NMR. The melting points of
the copolymers increased with the increasing insertion rate
of N-acetyl-O-(hex-5-enyl)-L-tyrosine ethyl ester as a result
of the hydrogen bonding interaction between the branch
chains. GPC results exhibited that MWs of the copolymers
were at the range of 9.3 9 104–3.79 9 105 g/mol. How-
ever, MWs of the copolymers were lower than those of the
homopolymers, and MWDs of the copolymers were
broader. This indicated that the chain transfer took place
during the copolymerization when N-acetyl-O-(hex-5-
enyl)-L-tyrosine ethyl ester was added into the polymer-
ization system. These catalysts were also favorable for the
homopolymerization of ethylene. The highest catalytic
activity was up to 1.66 9 106 g PE (mol Zr)-1 h-1 by
Cat.2 for ethylene polymerization. MWs of the poly-
ethylene were high up to 8.65 9 105 g/mol. MWDs of the
copolyethylene were about 3, implying that the copoly-
merization behavior followed the single mechanism.
Acknowledgments We sincerely thank the National Natural Sci-
ence Foundation of China (No. 21174011 and U1462102).
27. Bishop CJ, Ketola TM, Tzeng SY, Sunshine JC, Urtti A, Lem-
metyinen H, Laukkanen EV, Yliperttula M, Green JJ (2013) J Am
Chem Soc 135:6951–6957
28. Patri AK, Majoros IJ, Baker JR (2002) Curr Opin Chem Biol
6:466–471
29. Grodzinski J (1999) J React Funct Polym 39(2):99–138
30. Hsieh ET, Randall JC (1982) Macromolecules 15:1402–1406
31. Fan XY (2003) Life Sci Res 7:83–87
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