UHMWPE with short-chain branches synthesized by alkenyl substituted phenoxy–imine catalysts in ethylene polymerization

Article abstract of DOI:10.1002/pola.28265

The alkenyl substituted phenoxy–imine complexes [2-C₃H₅-6-(2, 3, 5, 6-C₆F₄H-N?CH)C₆H₃O]₂TiCl₂ (C₃H₅=?CH₂? CH?CH₂ or ?CH?CH?

Full text of DOI:10.1002/pola.28265

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UHMWPE with Short-Chain Branches Synthesized by Alkenyl Substituted
Phenoxy–Imine Catalysts in Ethylene Polymerization
Yi Wang, Hong Fan, Bo-Geng Li
State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University,
Hangzhou 310027, People’s Republic of China
Correspondence to: H. Fan (E-mail: hfan@zju.edu.cn)
Received 18 May 2016; accepted 14 August 2016; published online 00 Month 2016
DOI: 10.1002/pola.28265
ABSTRACT: The alkenyl substituted phenoxy–imine complexes
[2-C3H5-6-(2, 3, 5, 6-C6F4H-N@CH)C6H3O]2TiCl2 (C3H55ACH2A
CH@CH2 or ACH@CHACH3) are synthesized and characterized
by 1H NMR, 13C NMR, and elemental analysis. When activated
by MAO, they show high activity for the polymerization of eth-
ylene to UHMWPE under different conditions (temperatures
and polymerization time). Most of the resulting polymers have
high molecular weights (>1.0 3 106 gꢀmol21) and high melting
points as well as crystallinity. To clarify the effect of the alkenyl
group on the catalytic performance and the resultant polymer
microstructure, the corresponding saturated complexes of type
[2-C3H726-(2, 3, 5, 6-C6F4H-N@CH)C6H3O]2TiCl2 where C3H7 5 –
CH2ACH2ACH3 or ACH(CH3)2 were synthesized and tested as
catalysts in ethylene polymerization under the same reaction
conditions. The microstructure and morphologies of these two
species of PE samples were fully compared by the analysis of
13C NMR, GPC, DSC, and SEM. As a result, the allyl substituted
complex show the highest activity to prepare the highest
molecular weight polyethylene of all the catalysts. An interest-
ing feature of the UHMWPE produced by these four catalysts is
that they contain only a few short-chain branches (mainly
methyl, isobutyl and 2-methylhexyl branches) in a low amount
C
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(<2.7 branches/1000 C). 2016 Wiley Periodicals, Inc. J. Polym.
Sci., Part A: Polym. Chem. 2016, 00, 000–000
KEYWORDS: alkenyl substituents; ethylene polymerization; phe-
noxy–imine catalysts; short-chain branches; UHMWPE
be easily obtained by changing the cocatalyst or modifying
the precatalyst structure. In 2010, Mark and Enders7 modi-
fied methylaluminoxane (MAO) with 9-borabicyclo[3.3.1]
nonane (9-BBN) to activate organochromium to obtain
high molecular weight polyethylene (Mw5(0.43–4.89)3106
gꢀmol21, PDI 5 2.7–6.0). Romano and Rastogi8 then synthe-
sized UHMWPE with a Mw > 4 3 106 gꢀmol21 (PDI 5 2.4–
2.7) by using 2,6-di-tert-butyl-4-methylphenol (BHT) modi-
fied MAO to activate the complex [2-C(CH3)3-6-(C6F5-
N@CH)C6H3O]2TiCl2. Another method to increase the molec-
ular weight of polyethylene has been to introduce x-alkenyl
substituents to the catalyst to generate the “self-
immobilized” one. One of the earliest reports of this method
was when Alt and Red9 synthesized several x-alkenyl (C53 –
C57 ) substituted constrained geometry catalysts (CGCs) and
the corresponding x-alkyl-ended CGCs for comparison.
Higher molecular weight PE with broader MWD (Mw5(0.57–
2.20)3106 gꢀmol21, PDI 5 3.29–21.71) was obtained by the
x-alkenyl-substituted complexes compared with the corre-
sponding x-alkyl-substituted complexes under identical con-
ditions (1MPa, toluene, 60 8C, 1 h, Al/M 5 2500). Alt10
proposed that the x-alkenyl-substituted catalysts could be
INTRODUCTION Ultra high molecular weight polyethylene
(UHMWPE1) is a useful material that exhibits attractive
properties such as high impact resistance, extremely high
specific strength, abrasion resistance, a low dielectric con-
stant, an anti-ballistic nature, and excellent chemical, ultravi-
olet and moisture resistance.2 For these reasons, UHMWPE
has been widely applied in the manufacture of artificial
bones, prosthetic limbs, helmets, bulletproof vests, protective
armors, fish wires, marine engineering cables, and fortified
cockpit doors of aircrafts.2–4 However, the fabrication and
processing of UHMWPE in some valuable products such as
joint/hip replacement materials require polyethylene that
has a uniform chain distribution. Therefore, conventional
polyolefin catalysts for the production of UHMWPE need to
be improved to achieve this level of uniformity.5
The development of single site olefin polymerization cata-
lysts, such as metallocene and post-metallocene catalysts,
has allowed for better control over polyolefin microstructure
than Z-N catalysts in terms of molecular weight (number or
weight average molecular weight – Mn or Mw), molecular
weight distribution (MWD), comonomer incorporation, and
stereospecificity.6 It has also been found that UHMWPE can
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SCHEME 1 (A) The classic self-immobilization mechanism of the x-alkenyl substituted CGCs and (B) synthesis route of complexes
1–4.
incorporated in the propagating polymer chains to generate
the heterogeneous multinuclear network of active sites
[Scheme 1(A)]. This mechanism is the classic “self-
immobilization” theory. Later, Ivancheva and Malinskaya11
obtained UHMWPE (Mg > 2 3 106 gꢀmol21) by using the
functionalized complexes [2-C(CH3)3-6-(4-(OCH2-CH@CH2)
C6H4AN@CH)C6H3O]2TiCl2 and [2,4-(C(CH3)3)2-6-(4-(OCH2-
CH@CH2)C6H4-N@CH)C6H3O]2TiCl2 as polymerization cata-
lysts under standard conditions (0.3 MPa, toluene, 20–80 8C,
6-(2,6-F2-3,5-X2-C6F2X2H-N@CH)C6H3O]2TiCl2 (R@H or CH3,
X 5 H or F). However, these complexes produced higher
molecular weight polyethylene with a wider MWD than
those only bearing H atoms on the aniline skeleton. By opti-
mizing the complex structure, UHMWPE (Mw > 1 3 106
gꢀmol21, PDI 5 1.4) with a narrow MWD had been obtained
by using the complex [2-CH3-6-(4-(4-CH2@CHC6H4)-2, 3, 5,
6-C6F4-N@CH)C6H3O]2TiCl2. We further improved this class
of catalysts by synthesizing [2-C(CH3)3-6-(4-(4-CH2)@CH
C6H4)-2, 3, 5, 6-C6F4-N@CH)C6H3O]2TiCl2 and testing its eth-
ylene polymerization behavior with MAO as a cocatalyst.14
From the polymerization results, we knew that the complex
1
h). However, the UHMWPE obtained by the “self-
immobilization” method had a relative wide MWD. To get a
narrower distributed molecular weight polyethylene, we
must select a catalyst that has a strong control over chain
distributions to be modified with x-alkenyl substituent.
exhibits good to high activity (0.77–1.3 kgꢀmmol Ti21ꢀh21
)
with varying polymerization time and that UHMWPE
(Mw > 1.5 3 106 gꢀmol21, PDI 5 1.7) with a narrow MWD
could be synthesized under mild conditions.
The phenoxy–imine titanium catalysts with o-F substitution
showed an ability to produce high molecular weight polyeth-
ylene with an extremely narrow MWD by “living” polymeri-
zation.12 It would be really interesting to introduce both the
o-F and x-alkenyl substitutions to the phenoxy–imine cata-
lysts to obtain the UHMWPE with a wider MWD but in an
acceptable range by ethylene polymerization. In our previous
work investigating this catalyst system,13 six complexes were
synthesized. Three of these complexes [2-R-6-(2,6-F2-3,5-X2-
4-(4-CH2 5 CHC6H4)C6F2X2-N@CH)C6H3O]2TiCl2 (R@H or
CH3, X 5 H or F) contained 4-vinylphenyl groups and exhib-
ited lower activity compared with the other complexes [2-R-
Modifying the catalyst structure through the introduction of
a double bond-ended group to a suitable position of the cat-
alyst skeleton has shown great promise for the production of
polyethylene with high molecular weight and a narrow
MWD. Inspired by this discovery, we introduced an allyl
group ortho to the phenoxy-oxygen atom to obtain the com-
plex [2-(CH2-CH@CH2)-6-(2, 3, 5, 6-C6F4H-N@CH) C6H3O]2
TiCl2 and tested its ethylene polymerization behavior
[Scheme 1(B)]. Furthermore, by changing the substituent
ortho to the phenoxy-oxygen atom from the allyl group to
the 1-propenyl, n-propyl or isopropyl group, three of these 2,
2
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3, 5, 6-tetrafluorinated complexes [2-R-6-(2, 3, 5, 6-C6F4H-
N@CH)C6H3O]2TiCl2 (R5ACH@CH–CH3, ACH2CH2CH3 or
ACH(CH3)2) were synthesized and served as control groups
to clarify the effect of the allyl substituent in ethylene poly-
merization. This research also provides insight into the rela-
tionship between these 2, 3, 5, 6-tetrafluorinated complexes
and the microstructure of the resultant PEs.
13C NMR spectra for the PE samples were recorded on a
Bruker Avance 400 (100.6 MHz) pulsed spectrometer using
1, 2-C6D4Cl2 as solvent at 125 8C. The 13C NMR experiment
parameters were optimized for
a quantitative analysis,
including measuring the 908 pulse angle, inverse-gated pro-
ton decoupling, the calculation of an 8 s pulse delay time,
1 s acquisition time, and a 21,000 Hz spectral width. Approx-
imately 5200 scans were collected for data averaging. The
peak with highest intensity was referenced to 30.27 ppm.
EXPERIMENTAL
DSC measurements of the polymer melting points and
enthalpies were also conducted using the Perkin-Elmer DSC
7 instrument. Sample of 5–8 mg was measured by the fol-
lowing temperature program: (1) heating phase from 40 8C
to 160 8C (10 8Cꢀmin21); (2) isothermal phase at 160 8C for
5 min; (3) cooling phase to 40 8C (210 8Cꢀmin21); (4) iso-
thermal phase at 40 8C for 3 min; (5) heating phase from
40 8C to 160 8C (10 8Cꢀmin21).
Solvents and Reagents
All manipulations of air and moisture-sensitive compounds
were carried out under an atmosphere of dry nitrogen using
standard Schlenk technique or in a glovebox. The solvents
diethyl ether, toluene, methylene chloride (CH2Cl2), hexane,
tetrahydrofuran (THF), and acetonitrile (CH3CN) used in the
syntheses of the complexes and in polymerization reactions
were purchased from Hangzhou Chemical Reagents Company
and were refluxed over sodium or potassium using ben-
GPC was performed on a Viscotek 350A HT-GPC System
instrument in 1, 2, 4-trichlorobenzene at 150 8C under flow
rate of 1 mLꢀmin21, with a differential reflective index (DRI)
detector, a four-capillary viscometer detector, a right-angle
laser light scattering detector, and a 78 low angle laser light
scattering detector. A calibration curve was established using
polystyrene (PS) standards purchased from Malvern. The
DRI increment dn/dc was 0.054 mLꢀg21 for PS and 20.105
mLꢀg21for PE.
zophenone as
a moisture indicator under a nitrogen
atmosphere prior to use. 2, 3, 5, 6-Tetrafluoroaniline, 3-allyl-
salicylaldehyde, 2-isopropylphenol, MgCl2, TiCl4 (1 M in
CH2Cl2), n-BuLi (1.6 M in hexane), Pt-PMVS (poly(methylvi-
nylsiloxane) chelated H2PtCl6,
1 wt%), triethoxysilane,
MAO(1.4 M in toluene), CDCl3, and 1, 2-C6D4Cl2 were pur-
chased from Energy Chemical Company and used as
received. NaCl, Na2SO4, PSTA, paraformaldehyde, triethyl-
amine, HCl (36.5 wt%), and absolute ethanol were purchased
from Sinopharm Chemical Reagent Co., Ltd and used as
received. Polymerization grade ethylene was purchased from
Nanjing Wetry Gas Co., Ltd and was purified by passage
through an ethylene/propylene purifier consisting of a dehy-
dration column and a deoxygenation column provided by
Dalian Shengmai Gas Separation Engineering Co., Ltd.
The surface morphology of the samples was investigated
using a scanning electron microscope S-3700N (Hitachi,
Japan) equipped with an energy dispersive X-ray spectrome-
ter (EDX) for local and area distribution analysis of elements.
Imaging of sample surfaces was performed in high-vacuum
mode using accelerating voltages of 5 kv and a second elec-
tron (SE) detector. Coating of the sample surface was done
by spraying a platinum powder.
Characterization
FT-IR spectra of all organic compounds were determined on
a Nicolet 5700 spectrophotometer. Liquid samples were dis-
tributed as a thin layer on KBr disks and solid samples were
prepared as powder pills using KBr. NMR spectra of all
organic compounds and complexes were recorded on a
Synthesis of Compounds a–e
3-Isopropylsalicylaldehyde and four bidentate salicylaldimi-
nato chelating ligands bearing different C3 groups were syn-
thesized according to literature procedures.15,16
1
Bruker Avance 400 (400 MHz for H and 101 MHz for 13C)
2-(CH2ACH@CH2)-6-(C6F4H-N@CH)C6H3OH (a)
spectrometers and chemical shifts were referenced internally
with respect to CDCl3 (d 5 7.26 and (77.16 6 0.06) ppm,
respectively). High resolution mass spectra of organic com-
pounds were collected on a GCT Premier GC-TOFMA instru-
ment with an APCI method. Elemental analysis of all organic
compounds and complexes were performed on a CE EA1112
instrument. DSC measurements for melting point determina-
tions were performed using a Perkin-Elmer DSC 7 instru-
ment with ultra-high pure N2 gas purging through the
calorimeter at a flow rate of 20 mLꢀmin21. The temperature
and heat capacity of the instrument were initially calibrated
Mp 73–74 8C; 1H NMR (400 MHz, CDCl3, d): 12.62 (s, 1H,
OH), 8.81 (s, 1H, CH@N), 7.33 (d, J 5 7.4 Hz, 1H; Ar-H), 7.27
(dd, J 5 7.7, 1.5 Hz, 1H; Ar-H), 6.99–6.86 (m, 2H, Ar-H), 6.04
(ddt, J 5 16.8, 10.1, 6.6 Hz, 1H; @CHA), 5.15–5.06 (m, 2H,
5CH2), 3.47 (d, J 5 6.6 Hz, 2H; ACH2A); 13C NMR (101 MHz,
CDCl3, d): 170.80 (CH@N), 159.42 (ArC-OH), 136.17, 135.15,
131.53, 128.80, 119.23, 118.27, 116.03 (ArC or ACH@CH2),
102.49 (p-ArC in aniline), 33.48 (ACH2A); IR (KBr):
m 5 3425 (s; m(OAH)), 2912 (w; mas(CH2)), 1603 (s; ms(C@C)),
1575 (s; m(C@N)),1396(m; das(CH3)), 1362 (m; ds(CH3)),
1269 (m; b(OAH), 1232 (m), 1170 (m), 1078 (w), 1041 (s;
b(5CAH)), 1013 (w; ms(CAF)), 994 (w; c(5CAH)),
914 cm21 (m; c(5CAH)); HRMS (APCI, m/z): M1 calcd for
C16H11F4NO, 309.0777; found, 309.0778. Anal. calcd for
with an indium standard at a heating rate of 10 8Cꢀmin21
.
Sample of 5–8 mg was heated from 30 8C to 140 8C at a rate
of 10 8Cꢀmin21
.
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C16H11F4NO: C 62.14, H 3.59, N 4.53; found: C 62.29, H 3.52,
N 4.52%.
13C NMR (101 MHz, CDCl3, d): 171.02 (CH@N), 159.09
(ArCAOH), 137.14, 131.61, 130.92, 119.25, 118.12, 102.61
(ArC), 102.27 (p-ArC in aniline), 26.42 (ACH<), 22.37 (CH3);
IR (KBr): m 5 3416 (s; m(OAH)), 3087 (w; m(Ar-H)), 2957 (m;
mas(CH3)), 1570 (s; m(C@N)), 1459 (m), 1388 (m; das(CH3)),
1361(m; ds(CH3)), 1310(m), 1266 (m; b(OAH), 1225 (m),
1174 (m), 1147(m), 1103 cm21(w); HRMS (APCI, m/z):
calcd for C16H13F4NO, 311.0933; found, 311.0930. Anal. calcd
for C16H13F4NO: C 61.74, H 4.21, N 4.50; found: C 62.11, H
4.19, N, 4.40%.
2-(CH@CH–CH3)-6-(C6F4H-N@CH)C6H3OH (b)
Mp 113–115 8C; 1H NMR (400 MHz, CDCl3, d): 12.81 (s, 1H,
OH), 8.82 (s, 1H, CH@N), 7.56 (d, J 5 7.6 Hz, 1H; Ar-H), 7.26
(d, J 5 6.5 Hz, 1H; Ar-H), 7.03–6.86 (m, 2H, Ar-H), 6.78 (d,
J 5 17.4 Hz, 1H; Ar-CH@), 6.36 (dq, J 5 15.9, 6.6 Hz, 1H;
5CHA), 1.94 (dd, J 5 6.6, 1.7 Hz, 3H; CH3); 13C NMR (101
MHz, CDCl3, d): 170.76 (CH@N), 158.41 (ArCAOH), 135.20,
131.73, 127.86, 127.18, 124.56, 119.32, 118.62 (ArC or
ACH@CHA), 102.56 (p-ArC in aniline), 19.00 (CH3); IR(KBr):
m 5 3416(s; m(OAH)), 2966 (w; mas(CH3)), 2877 (w; ms(CH3)),
1599 (s; ms(C@C)), 1578 (s; m(C@N)), 1398 (m; das(CH3)),
1368(m; ds(CH3)), 1302(w), 1263 (m; b(OAH)), 1228 (m),
1043 (m; b(5CAH)), 1013 cm21 (w; ms(CAF)); HRMS (APCI,
m/z): M1 calcd for C16H11F4NO, 309.0777; found, 309.0775.
Anal. calcd for C16H11F4NO: C 62.14, H 3.59, N 4.53; found: C
62.45, H 3.72, N 4.41%.
Synthesis of Complexes 1–4
[2-(CH2ACH@CH2)-6-(C6F4H-N@CH)C6H3O]2TiCl2 (1)
To a stirred solution of N-(3-allylsalicylidene)-2, 3, 5, 6-
tetrafluoro aniline (0.309 g, 1 mmol) in dry diethyl ether
(10 mL) at 278 8C, 2.5 M n-butyllithium hexane solution
(0.4 mL, 1 mmol) was added dropwise over 5 min. The mix-
ture was allowed to warm to room temperature and stirred
for 3 h. The resultant mixture was added dropwise over 13
min to a 1 M CH2Cl2 solution of TiCl4 (0.5 mL, 0.5 mmol) in
dried diethyl ether (2 mL) at 278 8C. The mixture was
allowed to warm to room temperature and stirred for 19 h.
Concentration of the reaction mixture in vacuo gave a crude
product. Dry CH2Cl2 (6 mL) was added to the crude product,
the mixture was stirred for 5 min, the mixture was then
filtered. The solid residue was washed with dry CH2Cl2
(3 mL 3 2), and the combined organic filtrates were concen-
trated in vacuo to afford a dark red solid. Dry diethyl ether
(1.5 mL) and dry hexane (10 mL) were added to the solid,
stirred for 15 min, and then filtered after 70 min of standing.
The resultant solid was washed with dry hexane (10 mL 3
3) and dried in vacuo to give complex 1 (0.302 g, 0.410
mmol) as a brick red powder in 82.1% yield. 1H NMR (400
MHz, CDCl3, d): 8.26 (s, 2H, CH@N), 7.44 (d, J 5 7.2 Hz, 2H;
Ar-H), 7.31 (d, J 5 7.7 Hz, 2H; Ar-H), 7.00 (t, J 5 7.6 Hz, 2H;
Ar-H), 6.88–6.75 (m, 2H, Ar-H), 5.86 (ddt, J 5 16.9, 10.0, 6.9
Hz, 2H; @CHA), 5.18 (dd, J 5 17.0, 1.5 Hz, 2H; 5CH2), 5.09
(dd, J 5 10.0, 1.0 Hz, 2H; 5CH2), 3.34 (dd, 15.6, 6.6 Hz, 2H;
ACH2A), 3.00 (dd, J 5 15.6,7.2 Hz, 2H; ACH2A); 13C NMR
(101 MHz, CDCl3, d): 171.16 (CH@N), 160.14 (ArCAO),
137.03, 133.94, 132.55, 127.93, 121.72, 120.97, 116.19 (ArC
or ACH@CH2), 102.69 (p-ArC in aniline), 32.48 (ACH2A);
Anal. calcd for C32H20O2N2F8TiCl2: C 52.27, H 2.74, N 3.81;
found: C 51.86, H 2.65, N 3.75%.
2-nPr-6-(C6F4H-N@CH)C6H3OH (c)
Mp 77–78 8C; 1H NMR (400 MHz, CDCl3, d): 12.57 (s, 1H,
OH), 8.83 (s, 1H, CH@N), 7.33 (d, J 5 7.4 Hz, 1H; Ar-H), 7.25
(d, J 5 1.6 Hz, 1H; Ar-H), 6.94 (ddd, J 5 15.0, 9.9, 7.4 Hz, 2H;
Ar-H), 2.80–2.58 (m, 2H, Ar-CH2A), 1.79–1.62 (m, 2H,
ACH2CH3), 0.99 (t, J 5 7.4 Hz, 3H, CH3); 13C NMR (101 MHz,
CDCl3, d): 170.92 (CH@N), 159.69 (ArCAOH), 135.20,
131.12, 119.03, 118.17 (ArC), 102.34 (p-ArC in aniline),
31.59 (ArC-CH2), 22.57 (ACH2–CH3), 14.03 (CH3); IR(KBr):
m 5 3421 (s; m(OAH)), 2960 (m; mas(CH3)), 2924 (m;
mas(CH2)), 2866 (m; ms(CH3)), 1576 (s; m(C@N)), 1398(m;
das(CH3)), 1363(m; ds(CH3)), 1266 (m; b(OAH)), 1239 (m),
1170 (m), 1005 cm21 (w; ms(C-F)); HRMS (APCI, m/z): M1
calcd for C16H13F4NO, 311.0933; found, 311.0937. Anal. calcd
for C16H13F4NO: C 61.74, H 4.21, N 4.50; found: C 59.88, H
4.41, N 4. 30%.
3-Isopropylsalicylaldehyde (d)
1H NMR (400 MHz, CDCl3, d): 11.37 (s, 1H, OH), 9.87 (s, 1H,
CH@O), 7.46 (d, J 5 7.5 Hz, 1H; Ar-H), 7.39 (d, J 5 9.3 Hz,
1H; Ar-H), 6.98 (t, J 5 7.6 Hz, 1H; Ar-H), 3.37 (dt, J 5 13.8,
6.9 Hz, 1H; ACH<), 1.25 (d, J 5 6.9 Hz, 6H; CH3); 13C NMR
(101 MHz, CDCl3, d): 196.87 (CH@O), 159.23 (ArCAOH),
137.00, 133.58, 131.29, 120.18, 119.60 (ArC), 26.25
(ACH<), 22.22 (CH3); IR (KBr): m 5 3287 (m; m(OAH)), 3048
(m; m(Ar-H)), 2964 (m; mas(CH3)), 2870 (m; ms(CH3)), 2843
(m; ms(-CH<)), 2745 (w; m(O 5 CAH)), 1616 (s), 1439 (s),
1386 (m; das(CH3)), 1363 (m; ds(CH3)), 1308 (s), 1265 (m;
b(OAH)), 1219 (s), 1175 (w), 1151 (m), 1109 (m), 1100
(m), 1050 (m; b(5CAH)), 968 (m; c(5CAH)), 924 (w;
c(5CAH)), 878 cm21 (m); HRMS (APCI, m/z): M1 calcd for
[2-(CH@CHACH3)-6-(C6F4H-N@CH)C6H3O]2TiCl2 (2)
Complex 2 was synthesized by the same method as complex
1. The product was obtained as a brick red powder in
84.2% yield (0.155 g, 0.211 mmol). 1H NMR (400 MHz,
CDCl3, d): 8.26 (s, 2H, CH@N), 7.55 (d, J 5 7.3 Hz, 2H; Ar-H),
7.29 (s, 2H, Ar-H), 7.00 (t, J 5 7.3 Hz, 2H; Ar-H), 6.76 (s, 2H;
Ar-H), 6.54 (dq, J 5 13.0, 6.4 Hz, 2H; Ar-CH5), 6.28 (d,
J 5 15.9 Hz, 2H; @CHA), 1.87 (d, J 5 6.2 Hz, 6H; CH3); 13C
NMR (101 MHz, CDCl3, d): 171.12 (CH@N), 158.83 (ArCAO),
134.48, 132.87, 129.69, 125.36, 123.24, 122.47, 121.17 (ArC
or ACH@CHA), 102.74 (p-ArC in aniline), 18.25 (CH3); Anal.
calcd for C32H20O2N2F8TiCl2: C 52.27, H 2.74, N 3.81; found:
C 52.02, H 2.69, N, 3.72%.
C10H12O2, 164.0837; found, 164.0839. Anal. calcd for
C10H12O2: C 73.15, H 7.37; found: C 72.34, H 7.14%.
2-iPr-6-(C6F4H-N@CH)C6H3OH (e)
Mp 60–62 8C; 1H NMR (400 MHz, CDCl3, d): 12.66 (s, 1H,
OH), 8.83 (s, 1H, CH@N), 7.41 (d, J 5 7.5 Hz, 1H; Ar-H), 7.24
(d, J 5 1.6 Hz, 1H; Ar-H), 6.94 (m, 2H, Ar-H), 3.45 (dt,
J 5 13.8, 6.9 Hz, 1H; ACH<), 1.28 (d, J 5 6.9 Hz, 6H; CH3);
4
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[2-nPr-6-(C6F4H-N@CH)C6H3O]2TiCl2 (3)
Complex 3 was synthesized by the same method as complex
1. The product was obtained as a brick red powder in
73.9% yield (0.273 g, 0.369 mmol). 1H NMR (400 MHz,
CDCl3, d): 8.26 (s, 2H, CH@N), 7.41 (dd, J 5 7.3, 0.9 Hz, 2H;
Ar-H), 7.28 (dd, J 5 7.8, 1.3 Hz, 2H; Ar-H), 6.98 (t, J 5 7.6 Hz,
2H; Ar-H), 6.81 (ddd, J 5 9.2, 8.0, 3.4 Hz, 2H; Ar-H), 2.60–
2.35 (m, 2H, Ar-CH2), 2.33–2.03 (m, 2H, Ar-CH2), 1.78–1.45
(m, 4H; ACH2ACH3), 0.95 (t, J 5 7.3 Hz, 6H; CH3); 13C NMR
(101 MHz, CDCl3, d): 171.12(CH@N), 160.51(ArCAO),
137.25, 132.18, 130.20, 121.69, 120.80 (ArC), 102.54 (p-ArC
in aniline), 30.47 (Ar-CH2), 21.73 (ACH2ACH3), 12.89 (CH3);
Anal. calcd for C32H24O2N2F8TiCl2: C 51.99, H 3.27, N 3.79;
found: C 51.75, H 3.21, N 3.69%.
[2-iPr-6-(C6F4H-N@CH)C6H3O]2TiCl2 (4)
Complex 4 was synthesized by the same method as complex
1. The product was obtained as a reddish brown powder in
82.1% yield (0.303 g, 0.410 mmol). 1H NMR (400 MHz,
CDCl3, d): 8.27 (s, 2H, CH@N), 7.48 (d, J 5 6.8 Hz, 2H; Ar-H),
7.28 (dd, J 5 7.7, 1.1 Hz, 2H; Ar-H), 7.02 (t, J 5 7.6 Hz, 2H;
Ar-H), 6.81 (dd, J 5 14.5, 7.9 Hz, 2H; Ar-H), 2.90 (hept,
J 5 6.8 Hz, 2H; ACH<), 1.19 (dd, J 5 24.0, 6.9 Hz, 12H; CH3);
13C NMR (101 MHz, CDCl3, d): 171.29 (CH@N), 160.02
(ArCAO), 136.13, 133.78, 131.99, 121.75, 121.06 (ArC),
102.78 (p-ArC in aniline), 26.59 (ACH<), 22.47 (CH3), 19.30
(CH3); Anal. calcd for C32H24O2N2F8TiCl2: C 51.99, H 3.27, N
3.79; found: C 51.29, H 3.30, N 3.82%.
FIGURE 1 1H NMR (A) and 13C NMR (B) spectra of complexes
1–4 in CDCl3.
Ethylene Polymerization
Ethylene polymerizations were performed at atmospheric
pressure in a distilled toluene solution using a 250 mL glass
reactor equipped with a mechanical stirrer. The reactor was
charged and evacuated three times with nitrogen and twice
ethylene. The purified toluene (100 mL) was introduced into
the ethylene-filled reactor and stirred vigorously (400 rpm).
The polymerization was initiated by injecting a toluene solu-
tion of MAO followed by injecting a toluene solution of the
complex into the reactor. After a certain polymerization time,
4 mL acidic ethanol (10 mL HCl/1000 mL ethanol) was
added to terminate the reaction and then a large amount of
acidic ethanol was added to wash and purify the resultant
mixture. The polyethylene was isolated by filtration, washed
with ethanol several times, and dried in vacuo to a constant
weight (60 8C, vacuum oven).
tetrafluoroaniline in ethanol at 85 8C afforded ligand e. Bis(phe-
noxy–imine) complexes 1–4 were produced in high yield by the
addition of ether solutions of the lithium salts of ligands a, b, c,
or d to 0.5 equiv ether solutions of TiCl4. The structures of
these complexes were determined by 1H NMR and 13C NMR.
1
The H NMR spectra of complexes 1–4 in CDCl3 show single,
sharp imine peaks around 8.2 ppm and mainly doublet or
multiplets peaks of protons in the aromatic region around 7
ppm (Fig. 1). The chemical shift at 6.8 ppm in each spectrum
indicates the presence of a para-proton of the aniline ring.
The resonance pattern corresponding to the different C3
groups of each complex is very distinct. The existence of a
terminal double bond in complex 1 is shown by resonances
at 5.09, 5.18, and 5.86 ppm while the presence of an intra-
molecular double bond in complex 2 is indicated by the
resonances at 6.28 and 6.54 ppm. For complex 3, the reso-
nances at 0.9–2.8 ppm show the presence of an n-propyl
group. In complex 4, the resonances at 1.19 and 2.90 ppm
show the presence of methyl or methine groups correspond-
ing to an isopropyl group. Solvent peaks such as diethyl
ether (3.5 ppm), dichloromethane (5.3 ppm), or hexane
(0.88 and 1.26 ppm) are visible in the spectra.
RESULTS AND DISCUSSION
Synthesis and Structural Analysis of Complexes 1–4
The synthesis of phenoxy–imine ligands a–d and complexes 1–
4 is summarized in Scheme 1(B). Ligand a was prepared by the
condensation reaction of 3-allylsalicylaldehyde and 2, 3, 5, 6-
tetrafluoroaniline in ethanol at 85 8C and purified by recrystalli-
zation. The isomerization and hydrogenation by hydrosilylation
of ligand a with HSi(OEt)3 afforded ligand b and c in one pot.
Compound
d was obtained by hydroformylation of 2-
isopropylphenol with (HCHO)n under catalysis by MgCl2. The
condensation reaction of compound d and 2, 3, 5, 6-
The 13C NMR spectra confirm the assignments of these com-
plexes. In general, the chemical shifts around 171 ppm, 160
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TABLE 1 Results of Catalytic Ethylene Polymerization with Complexes 1–4/MAO
1st Heating
2nd Heating
Time
Mw
Mn
PDI IVc
Runa Cat T (8C) (min) Ab
(106g/mol) (106g/mol)
(dL/g) Tm (8C) DHf (J/g) ve (%) Tm (8C) DHf (J/g) ve (%)
d
d
1
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
4
4
4
4
4
10
30
50
30
30
10
30
50
30
30
10
30
50
30
30
10
30
50
30
30
30
30
30
15
60
30
30
30
15
60
30
30
30
15
60
30
30
30
15
60
2.7
3.1
2.2
3.4
2.5
2.5
4.2
2.1
2.0
5.4
1.5
1.6 19.5
1.6 29.7
2.0 16.7
1.1 17.3
1.3 34.8
1.9 6.89
1.5 10.4
1.6 10.8
2.4 5.92
1.3 15.8
1.2 13.6
1.1 21.1
1.6 13.7
1.2 11.5
3.2 24.2
1.3 9.32
1.2 17.1
1.3 16.8
1.1 11.4
3.4 22.9
139.9
140.1
140.7
140.1
140.5
137.9
139.5
139.9
138.1
139.9
140.7
139.5
138.9
139.7
140.8
139.6
140.1
140.9
139.6
141.2
215
228
221
222
227
221
219
207
204
212
226
236
230
237
229
224
231
231
231
232
74.9
79.3
76.9
77.3
78.8
76.8
76.3
72.2
70.9
73.8
78.6
82.3
80.0
82.3
79.8
78.0
80.3
80.5
80.3
80.8
134.4
134.3
133.9
134.8
133.6
133.8
135.0
134.3
134.6
134.2
135.2
133.9
133.6
134.8
134.3
134.4
134.3
134.2
134.2
134.2
103
108
109
99.3
96.6
138
126
106
130
105
117
113
124
127
109
134
109
106
122
111
35.9
37.5
37.8
34.6
33.6
48.1
43.8
37.0
45.1
36.7
40.8
39.3
43.0
44.3
37.8
46.7
37.9
36.7
42.5
38.7
2
2.6
3
1.0
4
1.9
5
4.2
6
0.25 0.74
0.56 1.3
0.51 1.2
0.71 0.66
0.66 1.9
0.40
0.85
0.74
0.28
1.4
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1.0
2.3
2.0
1.9
1.6
1.4
2.5
1.5
1.1
3.5
1.2
2.2
0.96
0.88
1.1
0.63 0.89
0.67
1.7
2.0
2.1
2.0
1.7
2.0
2.0
1.1
3.1
1.6
1.0
0.90
a
Conditions: 100 mL toluene, 1atm ethylene pressure, 30 8C, 2 lmol
capillary viscometer detector, a right-angle laser light scattering detec-
tor, and a 78 low angle laser light scattering detector. A calibration
curve was established using polystyrene (PS) standards purchased from
Malvern. The DRI increment dn/dc was 0.054 mLꢀg21 for PS and 20.105
mLꢀg21 for PE.
complex, 4 mmol Al.
b
Activity, 106 gPEꢀmolTi21ꢀh21
.
c
Determined by GPC using polystyrene calibration; IV means intrinsic
viscosity; GPC was performed on
a Viscotek 350A HT-GPC System
d
instrument in 1, 2, 4-trichlorobenzene at 150 8C under flow rate of 1
mLꢀmin21
Measured by DSC using the first heating curves.
e
,
with
a
differential reflective index (DRI) detector,
a
four-
On the basis of 100% crystalline polyethylene DHf0 5 287.3J/g.
ppm, and 102 ppm indicate the presence of the C@N group,
the aromatic carbon bound to oxygen and the aniline ring’s
carbon bound to hydrogen, respectively. For complex 1, the
resonances at 32.48 ppm show the presence of a methylene
group of the allyl substituent. However, for complex 2, the
resonances at 18.25 ppm indicate the presence of a methyl
group of the 1-propenyl substituent. The chemical shift of C3
group is much easier to be identified for the saturated com-
plexes. For instance, the n-propyl group of complex 3 is
assigned as the resonances at 12.89 ppm, 21.73 ppm and
30.47 ppm. The resonances at 19.30 ppm, 22.47 ppm, and
26.59 ppm in the spectrum of complex 4 show the presence
of an isopropyl group. All complexes have similar chemical
shift values for their aromatic rings and the main difference
in their spectra arises from their different substituents ortho
to the phenoxy-oxygen. Elemental analysis shows that these
complexes are highly pure.
the substituent ortho to the phenoxy-oxygen atom is varied
from propenyl to n-propyl or isopropyl, and then to allyl
group. In general, these complexes exhibit good to high
activity. Complex
1
exhibits higher activity (2.2–3.4
kgPEꢀmmolTi21ꢀh21) than the others under the same condi-
tions. Complexes 3 and 4 show moderate activity (0.63–2.3
kgPEꢀmmolTi21ꢀh21). However, the activity of complex 2
(0.25–0.71 kgPEꢀmmolTi21ꢀh21) decreases by an order of
magnitude compared with the others. Complexes 1–4 cata-
lyze ethylene polymerization with an inferior activity at
higher temperature and longer time as complexes of this
type have been shown to be unstable at certain tempera-
tures or long periods of time.12,17 The activity of complex 2
is much lower than complex 1, which can be only attributed
to the location of the double bond. The internal double bond
may coordinate more strongly to the Ti center than the ter-
minal double bond. Notably, the allyl substituted complex 1
shows a higher activity than the propyl substituted complex
3. Compared with the conventional “self-immobilized” cata-
lysts,9,14,18 complex 1 shows the opposite catalytic activity as
we might expect from the “self-immobilization” theory.
Ethylene Polymerization with Complexes 1–4
Table 1 shows that the catalytic activity of the complexes fol-
low the order of 2 < 3 ꢁ 4 < 1. Catalytic activity increases as
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Table 1 also shows that the molecular weight of PE obtained
by complexes follows the order of 2 < 3 ꢁ 4 < 1, which fol-
lows the catalytic activity trend. Out of all complexes, 2 pro-
duces the lowest molecular weight PE (Mw 5 0.66–1.9 3 106
gꢀmol21, Mn 5 0.28–1.4 3 106 gꢀmol21). 3 and 4 produce
moderate molecular weight polyethylene (Mw 5 0.89–3.5 3
106 gꢀmol21). In most cases, the molecular weight of poly-
ethylene produced by complex 1 (Mw 5 2.0–5.4 3 106
gꢀmol21, Mn 5 1.0–4.2 3 106 gꢀmol21) is larger than PE pro-
duced by 2, 3, and 4 under identical conditions. The highest
molecular weight polyethylene (Mw 5 5.4 3 106 gꢀmol21
,
Mn 5 4.2 3 106 gꢀmol21) obtained by complex 1 is a typical
UHMWPE with a small PDI value (polydispersity index,
PDI 5 1.3). Polymerization temperature and time can tune
the polyethylene molecular weight and polydispersity. By
raising the polymerization temperature, the Mw of PE tends
to increases first and then decreases. This indicates that the
chain transfer rate increases with increasing temperature.
The opposite trend of polydispersity variation was observed
which was ascribed to the nature of the active species that
are produced from the reaction between the complexes and
MAO.12,17 When increasing the polymerization time, the
molecular weight (Mw and Mn) of PE produced by the
alkenyl substituted complexes 1 and 2 increases. This
implies that complexes 1 and 2 have quasi living polymeriza-
tion characteristics. However, for the saturated complex 3 or
4, the Mn of PE decreased when reaction time increased
from 30 min to 60 min, which reflects a more serious chain
transfer in a longer time. In general, the MWD of PE tended
to be wider when increasing the polymerization time. How-
ever, some exceptions arise that the MWD of PE gets nar-
rower with prolonging the polymerization time (Nos 2,5;
Nos 9,7,10; Nos 12,14). For these complexes, they can pre-
pare the PE with Mw > 2.0 3 106 gꢀmol21, the ultra high
molecular weight component of which cannot pass through
the column filter and retrospectively the long chains are not
detected, thus reducing the values of PDI.
FIGURE 2 Thermal analysis of PEs obtained by cat 1–4: (a)
cooling; (b) heating.
than complex 2/MAO. It is possible that the smaller lameller
thickness and decrease in crystalline region of PE are caused
by the presence of an internal double bond rather than a ter-
minal double bond. However, complex 1/MAO produced PE
with a similar melting point and a lower crystallinity
compared with the PE produced by complex 3 or 4/MAO.
Therefore, a similar lameller thickness and higher level of
amorphous region of the PE was caused by terminal double
bond rather than saturated n-propyl or isopropyl substitu-
ents. These results suggest that the content of amorphous
region of the PE caused by the complexes follows the order
of 3 ꢁ 4 < 1 < 2.
In addition, Table 1 shows the first DSC heating scan analysis
of the nascent PEs obtained by complexes 1–4/MAO. This
reflects the nascent crystallization of the polymer chain in
the polymerization process. The polymers obtained are high-
ly crystalline HDPEs with the high melting points (Tm 5
137.9–141.2 8C) and crystallinity (v 5 70.9–82.3%). For com-
plexes 1, 2, and 4/MAO, the melting point of the obtained
polyethylene increases with increased polymerization tem-
perature and time which indicates an increased lameller
thickness of polyethylene. However, the melting point of the
polyethylene produced by complex 3/MAO decreased with
rising polymerization temperature and polymerization time
for the first 30 min at 30 8C. However, the melting point
increased during the polymerization time from 30 min to 60
min, still at 30 8C. This indicates a decreased lameller thick-
ness of polyethylene with increasing polymerization time
from 15 min to 30 min at 30 8C, but an increased lameller
thickness of polyethylene with increased polymerization time
from 30 min to 60 min at 30 8C. In general, complex 1/MAO
produced PE with a higher melting point and crystallinity
Figure 2 shows the re-crystallization and re-fusion processes
of the UHMWPEs synthesized by complexes 1–4/MAO from
the samples nos. 5, 10, 15, and 20 by erasing the thermal
history. A deviation between the Tc and Tm was observed
from the heating and cooling curves. From the cooling scans,
the highest crystallization point (114.8 8C) and the smallest
enthalpy (294.7 J/g) of all samples are observed on the
sample no. 5. From the second heating scans, the melting
points and crystallinity of the samples are around 134 8C
and 36%, respectively. This indicates that the constrains in
the amorphous region released upon first melting of the
nascent powder (Tm 5 140.5 8C, v 5 78.8%). Such constrains
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morphologies of the PE samples obtained by complexes 1
and 2/MAO are similar to the samples from complexes 3
and 4/MAO. It is certain that the catalysts formed from com-
plexes 1/MAO and 2/MAO are not heterogeneous during
ethylene polymerization.
Polyethylene Microstructure Analyzed
by 13C NMR Spectra
Figure 4 shows the 13C NMR spectra of PE samples obtained
with complexes 1–4/MAO. To have a reasonable spectrum,
over 5200 scans for 13 h must be accumulated. The micro-
structure determination of each sample is shown in Table 2
and the assignments are based on previous assignments.20–26
Three types of nomenclatures were used in Table 2. In the
fifth column, unit sequences are used where E is an ethylene
unit, P is a unit containing methyl branch, Y is a unit con-
taining isobutyl branch, and 2-MH is a unit containing a 2-
methylhexyl branch. The sequence unit (in the fifth column)
containing the carbon responded by the peak (in the second
column) is underlined. In the sixth column, the nomenclature
of Usami and Takayama was used.27 Branches were named
by xBn, where n is the length of the branch and x is the car-
bon number starting with the methyl as “1” for branches
and “br” for the backbone carbons. For paired branches, the
prefix “1, m” is used to notate how many m number of car-
bons are between two tertiary carbons. The backbone car-
bons between branches are designated by Greek letters by
primes.28 For the isobutyl and 2-methylhexyl branches BiBu
and B2MH are used, respectively. For the sake of clarity, the
last column of Table 2 shows the nomenclature of Carman
et al. and other researchers.29,30
FIGURE 3 SEM images of samples from Nos. 1, 6, 11, and 16
The presence of branches in the polyethylene obtained by
these FI-type catalysts used in ethylene homopolymerization
was first observed in the 13C NMR spectra. To determine the
branch types, several kinds of branches must be excluded.
No ethyl branches were observed as there was a lack of res-
onances near 11 ppm (1B2), 33.83 ppm (aB2), and 39.44
(a–d) and their magnified ones (e–h).
have enthalpic requirement in entropy gain on melting. The
lowest melting point (133.6 8C) belongs to the sample no. 5
which also possesses the lowest crystallinity (33.6%). In
general, UHMWPE produced by complex 1/MAO possessed
the highest level of amorphous region of all samples after
the first fusion treatment. For the melting processing of
UHMWPE, a lower chain entanglement of the nascent poly-
mer is favored as there is less difficulty with thermo-form-
ing.19 For the nascent powder of UHMWPE produced by
complexes 1–4/MAO, it is important to explore the relation-
ship between chain crystallization and chain entanglement in
our following work.
Polyethylene Morphology
Figure 3 shows the SEM images of the selected PE samples
under 500-fold and 5000-fold magnification. The basic shape
units of the PE samples include fibers, leaves and granules.
The fibers consist of highly ordered, nearly disentangled and
folded chain crystals and they make up the largest group in
the polymer matrix. A fibril-connected structure is observed
as well with mainly a block shape with gouges carved in the
block. However, no big spherical particles were observed in
the polymers obtained by complexes 1 and 2/MAO. The
FIGURE 4 The 13C NMR spectra of PE samples from nos. 1, 6,
11, and 16. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
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TABLE 2 Observed 13C Chemical Shift and Assignments of PE Samples from Nos. 1, 6, 11, and 16
Chemical Shift (ppm)
Peak No.
1
This Work
Literature
43.15
Ref
20
Sequence
EYYEY
Branched Unit
Carbon
1
43.20
43.15
43.14
41.06
38.47
38.45
36.31
33.79
33.63
26.31
26.29
25.78
25.44
25.42
25.41
24.65
24.64
aaBiBu
Saad
2
3
4
43.12
20–22
YYYE
YPP
aaBiBu
aaB1
Scaa
Scaa
Saa
41.80–42.70, 39–42
38.50, 38.87
23, 24
20–23, 25
EYYE
aaBiBu
5
6
35.70–36.50
25
E2MHE
EYE
brB2MH
brBiBu
CH
Tdd
33.62, 33.63, 33.70
20–23, 25
7
26.05
25
E2MHE
2B2MH
CH
8
9
25.80
25.38
23
25
EYE
2BiBu
CH
E2MHE
4B2MH
CH2
10
24.57, 24.54
20–22
YYEY
1,5-b0 BiBu
Sbb
ppm (brB2).27 No propyl branches were observed in the
spectra as there was an absence of the typical resonance at
36.72 ppm (3B3). Butyl branches should produce peaks at
23.37 ppm (2B4), 29.38 ppm (3B4), and 33.94 ppm (4B4)
which were also absent in the spectra. The inclusion of pen-
tyl branches was also discarded because of the absence of a
resonance at 32.65 ppm (3B5).
resonance at 41.06 ppm was assigned as paired 1,3-methyl
branches from 1,3-a0B1 carbons of PE produced by complex
1/MAO.
The presence of short isobutyl branches was identified by
the resonance of specified carbons (Scheme 2 and Table 2).
Isobutyl branches produced peak 6 (33.63 ppm or 33.79
ppm) of brBiBu and peak 8 (25.78 ppm) of 2BiBu. Further-
more, resonances from 38 ppm to 45 ppm revealed the pres-
ence of paired 1,3-isobutyl branches in different sequences.
The methylenic signals at 43.14 (or 43.13) ppm are assigned
to Scaa carbons, which are diagnostic of the YYYE sequence.
The resonances at 43.20 (or 43.15) ppm and 25.63–25.65
ppm are assigned to S1aar and Sbb carbons of the YYEY
sequence, respectively. At last, the peaks at 38.45 (or 38.47)
ppm exhibit the presence of Saa of the EYYE sequence.
The NMR of the PE produced by complex 1 is highly similar
in structure to the NMR of ethylene/4-methyl-1-pentene
copolymer. Each peak can be nearly matched to the NMR of
this polymer in the literatures with negligible difference. The
assignment for methyl isolated branches is the same as for
this copolymer found in multiple studies.27,28,31,32 The
The presence of 2-methylhexyl branches was also identified
by the typical chemical shift for this type of carbon (Scheme
2 and Table 2). The signals at 36.31 ppm, 26.31 (or 26.29)
ppm, and 25.41–25.44 ppm are assigned to the brB2MH
,
2B2MH, and 4B2MH carbons, respectively.
By using ASTM D5017-9630 and related references,28,33 the
branch density of the PE samples were calculated and are
displayed in Table 3. Only polyethylene produced by complex
1 contains three species of branches in the form of methyl,
isobutyl, and 2-methylhexyl branches and these account for
0.32, 1.15, and 0.39 branches/1000 C, respectively. The other
three PE samples produced by complexes 2–4/MAO contain
only two species of branches as isobutyl and 2-methylhexyl
branches. Across all PE samples, the branch density of the
PE obtained by complex 2/MAO was higher than the branch
SCHEME 2 The assignment of the peaks and the correspond-
ing structure.
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TABLE 3 Quantitative Results of Branching in PE Samples from
temperature solution process using the constrained geome-
try catalysts (CGC-Ti catalyst),35 and only ethyl branches
were found in the polyethylene produced by the meso-
(CH2)2(Ind)2ZrCl2 catalyst.36 By introducing x-alkenyl sub-
stituents to some Ti or Zr based catalysts, the branch struc-
tures of the resultant polyethylene would give a surprise.
The functional zirconocene catalyst (1-(9-Flu))(1-Cp)C(1-
CH3)(1-CH2-CH2-CH@CH2)ZrCl2 produced PE with evenly dis-
tributed ethyl branches across the whole MWD,37 however,
the functionalized CGC catalyst (3-((CH2)3CH@CH2)
Ind)Si(CH3)((CH2)5CH@CH2)N(C(CH3)3)TiCl2 produced PE
distributed with both ethyl and butyl branches at 90 8C.38
For the di-imine Ni/Pd catalysts, “chain walking” mecha-
nism34 had been used to account for the formation of
branches in the polyethylene; however, for the early-
transition metal catalysts, b-H transfer and the resultant
monomer reinsertion35,36 had been regarded as the mecha-
nism for explaining the formation of the branches.
Nos. 1, 6, 11, and 16
Branches/1000 C
Mw
(104gꢀmol21
Branches/
1000 C
Complex
)
Me
iBu
2MH
1
2
3
4
198
66
0.32
1.15
1.53
0.37
0
0.39
1.15
0.60
0
1.86
2.68
0.97
0
0
0
0
107
107
density of other PE samples and accounted for 2.68
branches/1000 C. Among the saturated C3 substituted cata-
lysts, complex 3/MAO produced PE with less branches than
the PE samples produced by complex 1 or 2/MAO. However,
complex 4/MAO produced highly linear polyethylene with
almost no branches.
To figure out how the branches formed in the ethylene
homopolymer and how much the influence of the catalyst
structure on the branch types, we searched for the related
literatures and the results are listed in Table 4. As a matter
of fact, n-alkyl branches (mainly methyl branches, others are
ethyl, propyl, butyl, pentyl, and hexyl branches), long
branches and branch-on-branch (i.e., sec-butyl) are present
in the polyethylene produced by di-imine Ni/Pd catalysts.34
However, for the early-transition metal catalysts, the branch
types of the resultant ethylene homopolymer are much few-
er. Only methyl branches and small amount of long branches
were detected in the polyethylene produced at high-
In this catalytic system, b-H elimination was strongly sup-
pressed due to the o-F structure of them (judged by the high
molecular weight of the prepared PE), the formation of
branches was probable related to a completely different
mechanism that needed to be further studied.
CONCLUSIONS
Four 2, 3, 5, 6-tetrafluorinated complexes 1–4 bearing
alkenyl or alkyl groups ortho to phenoxy-oxygen atom were
synthesized and fully characterized. When cocatalyzed by
MAO, the complexes exhibit good to high catalytic activity in
TABLE 4 Summary of the Branches Formation in Ethylene Homopolymers
Catalyst
Branch Types
Probable Mechanism
Chain walking
Ref.
34
Short branches(methyl, ethyl, propyl,
butyl, pentyl, and hexyl), long
branches and branch-on-branch
Methyl branches and small amount
of long branches
b-H elimination and 1,2-insertion
as well as 2,1-insertion of
macromonomer
35
36
Ethyl branches
b-H elimination and 1,2-insertion
as well as 2,1-insertion of
the resultant butylene
Evenly distributed ethyl branches
Ethyl and butyl branches
No mention
37
No mention
38
Complexes 1–3/MAO
Methyl, isobutyl(iBu), and 2-methyl-
hexy(2MH) branches
To be confirmed
This work
10
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