Polymerization and copolymerization of olefins and acrylates by bis(benzimidazole) copper catalysts

Article abstract of DOI:10.1021/ma034548c

CuBBIM/MAO is a highly versatile catalyst system that homopolymerizes ethylene and acrylates and, more significantly, induces ethylene/acrylate copolymerization. This new system is remarkable in spanning homopolymerization space broadly, while still enabling copolymerization of these traditionally transition-metal-catalyzed incompatible monomer classes.

Full text of DOI:10.1021/ma034548c

8
584
Macromolecules 2003, 36, 8584-8586
P olym er iza tion a n d Cop olym er iza tion of
Olefin s a n d Acr yla tes by Bis(ben zim id a zole)
Cop p er Ca ta lysts
Sch em e 1. Syn th etic Sch em e for th e P r ep a r a tion of
Bis(ben zim id a zole) Cop p er (II) Com p lexes 5-7
Rober t T. Stibr a n y,* Don a ld N. Sch u lz,
Sm ita Ka ck er , Abh im a n yu O. P a til, Lisa S. Ba u gh ,
Steven P . Ru ck er , Step h en Zu sh m a ,
En ock Ber lu ch e, a n d J osep h A. Sissa n o
Corporate Strategic Research, ExxonMobil Research and
Engineering Co., 1545 Route 22 East,
Annandale, New J ersey 08801
Received April 28, 2003
Revised Manuscript Received September 4, 2003
There has been considerable recent activity in the
1
,2
area of late transition metal polymerization catalysis.
In the past two decades, metallocenes have revolution-
ized the commercial polymerization of olefins. In many
cases, these catalysts are now used in place of tradi-
tional Ziegler-Natta catalysts to produce better per-
forming HDPE and LLDPE. Metallocenes are based on
early transition metals, predominantly Ti, Zr, and Hf.
These metals are very oxophilic and are very easily
initiators do not readily homopolymerize ethylene under
low-pressure, low-temperature conditions.
3
poisoned by polar monomers and contaminants. Cata-
We have discovered that certain bis(benzimidazole)-
ligated Cu precatalysts (activated by MAO) not only
homopolymerize both ethylene and various acrylates but
lysts with the ability to incorporate polar monomers
may give rise to new high-performance materials with
4
13
high adhesive, toughness, and dyability. These cata-
also copolymerize these two monomer classes. These
lysts may also be more tolerant of minor contaminants
in ethylene polymerization. The search for these types
of polymerization catalysts has led to the late transition
metals.
copper-based catalysts produce very highly linear poly-
ethylene as well as incorporate certain R-olefins.1
Unlike conventional Brookhart Pd diimine-catalyzed
ethylene/acrylate copolymers, the Cu-catalyzed copoly-
mers are in-chain copolymers with high levels of acry-
late incorporation, and a range of low to high molecular
weight products have been prepared. This paper details
the Cu bis(benzimidazole) (CuBBIM)/MAO-catalyzed
homo- and copolymerizations of ethylene and alkyl
(meth)acrylates and the characterization of the products
formed from these systems.
4
The copolymerization of olefins with acrylate mono-
mers by organometallic catalysts has been an elusive
goal. Late transition metal catalysts, in general, are less
sensitive to deactivation by polar species than metal-
locenes. However, the known late metal catalysts still
have difficulty preparing acrylate homopolymers and/
or in-chain olefin/acrylate copolymers. For example, the
salicylaldimine-ligated “neutral nickel” catalysts re-
These copper complexes are prepared in three syn-
thetic steps as illustrated in Scheme 1. The first step is
the acid-catalyzed condensation reaction of a dicarboxy-
lic acid in acid with 2 equiv of phenylenediamine.
Condensation of tartronic acid yields the carbinol-
bridged bis(benzimidazole), 1a (X ) -CHOH-). Con-
densation of malonic acid yields the methylene-bridged
5
ported by Grubbs only copolymerize ethylene with
functional monomers in which a spacer group separates
the functionality and the reactive double bond. Brook-
6
hart’s early cationic Pd and Ni diimine catalysts can
produce only low acrylate content ethylene copolymers
(
<20 mol %), which have the acrylate group at the ends
1
5
of branches rather than in the polymer backbone chain.
More recent versions of the Ni diimine catalysts are
bis(benzimidazole), 1b (X ) -CH2-). Condensation of
7
diphenic acid yields the 2,2′-biphenyl-bridged bis-
1
6
able to make in-chain copolymers, but they tend to be
low molecular weight materials with low incorporation
(benzimidazole), 1c (X ) 2,2′-biphenyl). The next
synthetic step is alkylation of the bis(benzimidazole).
Compound 1a can be alkylated sequentially up to four
times, once each at the protonated nitrogens, followed
by the carbinol and finally at the bridgehead carbon.
Compound 1b can be alkylated sequentially up to four
times, once each at the protonated nitrogens and twice
at the methylene bridgehead carbon. In this study 1b
was alkylated three times. Compound 1c was alkylated
twice, once at each protonated nitrogen, (4a ,17 4b).
Finally, the alkylated bis(benzimidazole)s are metalated
using CuCl2‚2H2O in a mixture of ethanol and triethyl
orthoformate (TEOF). Triethyl orthoformate is added
to effect the dehydration of the reaction mixture and
aid in the crystallization of the metal complex. The solid
crystalline complexes are then isolated by filtration.
Figure 1 shows an X-ray (ORTEP) structure for 5.18
8
of polar monomers (<1.4 mol %). Similarly, Drent’s
recently reported [P,O]-ligated Pd catalysts also tend
to produce low molecular weight, low acrylate content
copolymers.
With the exclusion of ATRP (atom transfer radical
polymerization) catalysts, which have been reported for
many transition metals, polymerization catalysts based
on copper are considerably rare. One rather ambiguous
9
example has been reported. One other example is
1
0
Shibayama’s aminidate-ligated Cu catalyst system;
however, only homopolymers have been reported with
these initiators. Cu ATRP catalysts can be exemplified
1
1
by the pioneering work of Matyjaszewki and more
recently of Sen.12 However, these systems are free
radical initiators, albeit living radical ones. Free radical
1
0.1021/ma034548c CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/24/2003

Macromolecules, Vol. 36, No. 23, 2003
Communications to the Editor 8585
Ta ble 2. Cop p er -Ca ta lyzed Cop olym er iza tion of Eth ylen e
a n d t-BAa
polymer
yield
(g)
n w
M , M ,
Cu/Al/t-BA
mole ratio
MWD
triads
branches/ mol %
b
(×10-
3
)
EAE:EAA:AAA 1000 C
t-BA
1
1
1
/230/1740
/130/1780
/230/950
6.0
5.9
2.4
39, 85, 2.2
44, 89, 2.0
6:35:58
6:34:60
11:35:54
0
6
10
65
72
55
a
Reaction conditions: 0.045 mmol of 7b; toluene as solvent;
exclusion of light; mol Al/MAO; 80 °C; 720 psig of ethylene;
concentration t-BA 1.9 M. b Mole fraction of the copolymer consist-
ing of t-BA units.
F igu r e 1. Molecular structure of 5. Selected bond lengths (Å)
and angles (deg): Cu-N43 1.951(3), Cu-N33 1.951(3), Cu-
Cl1 2.2336(10), Cu-Cl2 2.2283(12), N(43)-Cu-N(33)
tacticities of the CuBBIM/MAO-catalyzed polymers are
considerably different than those found for a free
radically prepared poly(t-BA).
9
1
1
1.06(11), N(43)-Cu-Cl(2) 101.69(9), N(33)-Cu-Cl(2)
29.58(9), N(43)-Cu-Cl(1) 126.28(9), N(33)-Cu-Cl(1)
04.64(9), Cl(1)-Cu-Cl(2) 105.96(4).
Ethylene and tert-butyl acrylate have been copoly-
merized at 600-800 psig and 80 °C using CuBBIM/
MAO catalysts. In contrast to the Brookhart Pd and Ni
diimine catalysts, high levels of acrylate incorporation
are possible (45-100 mol %). High molecular weight,
narrow MWD copolymers with low levels of branching
can be made (Table 2). The products have been shown
Ta ble 1. Cop p er -Ca ta lyzed Hom op olym er iza tion of t-BAa
Cu/Al/t-BA polymer
Mn, Mw,
tacticity mm,
mr, rr (%)
catalyst mole ratio yield (%) MWD (×10-3)
5
5
5
5
5
7
0/1/14
1/5/940
trace
5
13
to be true copolymers by C NMR and GPC/UV. The
1/12/1010
1/13/1320
1/12/980
1/10/980
33
57
77
52
280, 620, 2.2 16, 45, 39
470, 850, 1.8
320, 640, 2.0
1
3
C NMR spectra for the CuBBIM/MAO catalyzed
E/t-BA copolymers can be compared with homopoly-
(t-BA). The presence of EAE and EAA/AAE triads in the
former is a clear indication of copolymer formation.
Additional support for the presence of copolymers is a
uniform distribution of UV activities across the MWD
in the GPC/UV trace.
b
19, 43, 38
mm ) 44-46
mm ) 44
b
c
radical
radical
99
97
54, 89, 1.66
58, 92, 1.59
epimer- 1/12/1000
mm ) 45
d
ization
a
Reaction conditions: 0.045 mmol of catalyst; toluene as
While the mechanism of CuBBIM/MAO polymeriza-
tions is not fully determined, the ethylene homopolym-
erization data are consistent with a single-site coordi-
nation/insertion mechanism based upon the high degree
of linearity and narrow MWD in the product. Along with
the ability to incorporate certain R-olefins, this mech-
anism is further supported by indirect mechanistic
studies performed using fluorine-labeled copper cata-
b
solvent; exclusion of light; mol Al/MAO; 25 °C; 18 h. Reference
0. Polymers produced over a range of 0-60 °C. Poly(t-BA)
prepared with benzoyl peroxide as in ref 20. Epimerization
verification of polymer in footnote c. Mole ratio of t-BA based on
monomer segments.
c
2
d
Activation of 5-7 with MAO generates active polym-
erization catalysts that homopolymerize both ethylene
and acrylates, as well as copolymerize ethylene with
acrylates. Under the copolymerization conditions de-
scribed below, the order of monomer reactivity is tert-
butyl acrylate (t-BA) 3910 (mol of monomer/(g of Cu h))
1
4,22
lysts.
The acrylate homopolymerization and copo-
lymerization cases may proceed by a different or addi-
tional mechanism. However, conventional free-radical
or ATRP mechanisms are less likely. Conventional free-
radical chemistry is unlikely because CuBBIM/MAO
does not polymerize other traditional free-radical mono-
mers (e.g., styrene, butadiene, vinyl acetate) and can
induce polymerization in the presence of known free-
radical inhibitors such as phenothiazine or MEHQ.
(Commercial samples of acrylate monomers containing
10-100 ppm of inhibitor can be polymerized “as re-
ceived” without removal of inhibitor.) In our lab 6b
failed to induce ATRP with PhEtCl or reverse ATRP
with AIBN. Tacticities for acrylate homopolymers cata-
lyzed by CuBBIM/MAO do not match those expected for
>
n-butyl acrylate (n-BA) 1790 (mol of monomer/(g of
Cu h)) > methyl methacrylate (MMA) 860 (mol of
monomer/(g of Cu h)). CuBBIM/MAO does not homopo-
lymerize traditional free radically polymerizable mono-
mers such as styrene, vinyl acetate, or butadiene. Also,
unlike Brookhart’s Pd diimine catalysts, it does not
homopolymerize cyclopentene.19
Homopolymers of ethylene prepared by CuBBIM/
MAO at 700-800 psig ethylene, 80 °C, and Al/Cu ratio
of >200/1 are typically high molecular weight, very
linear, highly crystalline, and very high melting poly-
1
3
20
mers (Tm > 135 °C). The C NMR of HDPE prepared
by CuBBIM/MAO contains no detectable branches. This
is in contrast to the first-generation Brookhart Pd
diimine catalysts that often produce polymers with 80-
free-radical products. Attempts to epimerize a radi-
cally produced homopolymer of t-BA under CuBBIM/
MAO polymerization conditions failed to alter the
tacticity of the polymer. Additionally, room temperature
experiments monitoring the CuBBIM/MAO catalysis of
the homopolymerization of t-BA by EPR failed to detect
the presence of any radical or Cu(II) signal.
In summary, CuBBIM/MAO is a highly versatile
catalyst system that homopolymerizes ethylene and
acrylates and, more significantly, induces ethylene/
acrylate copolymerization. This new system is remark-
able in spanning homopolymerization space broadly,
while still enabling copolymerization of these tradition-
ally transition-metal-catalyzed incompatible monomer
classes.
1
50 branches/1000 carbons.21
Homopolymerization of acrylates by CuBBIM/MAO
is typically run at lower temperatures (∼25 °C) and
ratios of Al/Cu (<50). Table 1 shows the homopolymer-
ization of t-BA by these CuBBIM/MAO catalyst systems.
Conversion increases with increasing MAO/Cu ratio and
longer reaction times. Little or no polymer is formed in
1
the absence of the CuBBIM catalysts. GC and H NMR
analysis of the polymerization mixture showed only
monomer, polymer, and solvent. The resulting products
are high molecular weight, narrow MWD polymers. The

8
586 Communications to the Editor
Macromolecules, Vol. 36, No. 23, 2003
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