Copolymerization of ethene with styrene derivatives, vinyl ketone, and vinylcyclohexane using a (phosphine-sulfonate)palladium(II) system: Unusual functionality and solvent tolerance

Article abstract of DOI:10.1021/om800237r

A (phosphine-sulfonate)palladium(II) system catalyzes the copolymerization of ethene with a variety of styrene derivatives, including those with oxygen functionalities. The copolymerizations also proceed in protic solvents, including water, allowing metal-mediated emulsion copolymerization of ethene and styrene.

Full text of DOI:10.1021/om800237r

Organometallics 2008, 27, 3331–3334
3331
Copolymerization of Ethene with Styrene Derivatives, Vinyl Ketone,
and Vinylcyclohexane Using a (Phosphine-sulfonate)palladium(II)
System: Unusual Functionality and Solvent Tolerance
Sachin Borkar, David K. Newsham, and Ayusman Sen*
Department of Chemistry, The PennsylVania State UniVersity, UniVersity Park, PennsylVania 16802
ReceiVed March 13, 2008
was found to catalyze ethene homopolymerization with slightly
lower activity compared to the system generated in situ by
combining the 2-[bis(2-methoxyphenyl)phosphino]benzene-
sulfonic acid (P∼SO3H) ligand and bis(dibenzylideneacetone)-
palladium(0), Pd(DBA)2. However, unlike the system formed
in situ, 1 was unreactive toward the copolymerizations of ethene
with the polar vinyl monomers studied, presumably because they
are too weakly coordinating to displace the coordinated pyridine.
The addition of 1 or 2 equiv of the Lewis acid triphenylboron
(BPh3) creates a vacant coordination site on the metal center
and allows for easier coordination of the incoming monomer
and subsequent insertion into the Pd-CH3 bond.
Summary: A (phosphine-sulfonate)palladium(II) system cata-
lyzes the copolymerization of ethene with a Variety of styrene
deriVatiVes, including those with oxygen functionalities. The
copolymerizations also proceed in protic solVents, including
water, allowing metal-mediated emulsion copolymerization of
ethene and styrene.
The copolymers of ethene with styrene are of great current
interest because of their anticipated high viscoelasticity, compat-
ibility with other commodity polymers, and excellent mechanical
properties.1,2 Early transition-metal-based systems are known
to catalyze this copolymerization, but these cannot tolerate an
oxygen functionality on the styrenic monomer and protic
solvents cannot be employed for the reaction.3,4 Late-transition-
metal polymerization systems are known for the polymerization
of some monomers with oxygen functionalities.5,6 However,
few7–9 have been shown to be effective for copolymerization
of ethene with styrene; insertion of styrene typically leads to
chain termination through ꢀ-H elimination. Herein, we describe
the first well-defined system for the copolymerization of ethene
with a variety of styrene derivatives, including those with
oxygen functionalities. Moreover, it is possible to carry out the
copolymerizations in protic solvents, including water, allowing
for the emulsion copolymerization of ethene and styrene. The
same catalyst system can also be employed for the copolym-
erization of ethene with methyl vinyl ketone, vinylcyclohexane,
and other 1-alkenes.
The insertion of styrene into the Pd-CH3 bond of 1 in
dichloromethane-d2 was followed by in situ NMR spectroscopy.
At ambient temperature, 1 readily converts styrene to 1-phenyl-
1
1-propene in the presence of BPh3, as confirmed by H NMR
signals at 6.5 ppm (1H, d), 6.3 ppm (1H, m), and 1.9 ppm (3H,
d). This is consistent with a 2,1-insertion of styrene into the
Pd-CH3 bond followed by rapid ꢀ-H elimination to give a
palladium hydride and 1-phenyl-1-propene. Additionally, the
We and others10–13 have previously reported on the copo-
lymerization of ethene with polar vinyl monomers and nor-
bornene derivatives using the neutral (phosphine-sulfonate)-
based system described by Drent and Pugh.6 Compound 111
1
conversion of styrene to a second product was shown by H
NMR signals at 3.2 ppm (1H, q) and 0.7 ppm (3H, dd) along
with the replacement of the 31P NMR signal of 1 at 22.7 ppm
with a new signal at 11.4 ppm. These observations are consistent
with the 2,1-insertion of styrene into the Pd-H bond to give
an (η3-phenylethyl)palladium compound, 2, as shown in Scheme
1. COSY correlation and 1H NMR splitting in an isolated sample
of 2 were used to confirm the structure of the η3-phenylethyl
moiety. The mechanism is supported by the reaction of 1 with
styrene-d8 to produce 1-phenyl-1-propene-d7 with an unlabeled
methyl group and 2-d9 with a fully deuterated phenylethyl
moiety, as determined by H and H NMR spectroscopy. The
formation of an η3-phenylethyl species is supported by the
absence of pyridine or other ligands in the fourth coordination
site of Pd in isolated samples of 2 and the doublet of doublets
splitting of the CH3 group, which is consistent with the complex
* To whom correspondence should be addressed. E-mail: asen@psu.edu.
(1) Cheung, Y. W.; Guest, M. J. In Modern Styrenic Polymers:
Polystyrenes and Styrenic Copolymers; Scheirs, J., Priddy, S., Eds.; Wiley-
VCH: Weinheim, Germany, 2003; pp 605-630..
(2) Chum, P. S.; Kruper, W. J.; Guest, M. J. AdV. Mater. 2000, 12,
1759–1767.
(3) McKnight, A. L.; Waymouth, R. M. Chem. ReV. 1998, 98, 2587–
2598.
(4) Stevens, J. C.; Timmers, F. J.; Wilson, D. R.; Schmidt, G. F.; Nickias,
P. N.; Rosen, R. K.; Knight, G. W.; Lai, S. Y. Eur. Pat. Appl EP 0416815
A2, 1991.
(5) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169–1204.
(6) Drent, E.; Dijk, R.; Ginkel, R.; Oort, B.; Pugh, R. I. Chem. Commun.
2002, 744–745.
(7) Soula, R.; Saillard, B.; Spitz, R.; Claverie, J.; Llaurro, M. F.; Monnet,
C. Macromolecules 2002, 35, 1513–1523.
1
2
(8) Carlini, C.; Galletti, A. M. R.; Sbrana, G.; Caretti, D. Polymer 2001,
42, 5069–5078.
(9) Yuan, Q. L.; Zhao, C. B. China Patent CN 10107360, 2007.
(10) Liu, S.; Borkar, S.; Newsham, D.; Yennawar, H.; Sen, A.
Organometallics 2007, 26, 210–216.
(11) Newsham, D. K.; Borkar, S.; Sen, A.; Conner, D.; Goodall, B.
Organometallics 2007, 26, 3636–3638.
(12) Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. J. Am. Chem. Soc.
2007, 129, 8948–8949.
(13) Luo, S.; Vela, J.; Lief, G. R.; Jordan, R. F. J. Am. Chem. Soc.
2007, 129, 8946–8947.
10.1021/om800237r CCC: $40.75
2008 American Chemical Society
Publication on Web 07/01/2008

3332 Organometallics, Vol. 27, No. 14, 2008
Communications
Scheme 1. Conversion of 1 and Styrene to 2 and 1-Phenyl-1-propene through a Palladium Hydride Species
Table 1. Copolymerization using Complex 1 and Triphenylborona
comonomer
comonomer
(amt (g))
ethene pressure
(psi)
time
(h)
activity
incorp
entry
Mw (PDI)b
(g (mol of Pd)-1 h-1
)
(mol %)c
1
styrene (1)
styrene (5)
styrene (5)
VCH (1)
100
100
100
100
100
100
50
50
50
200
100
7
7
7
7
5
7100 (2.3)
4700 (1.8)
2000 (1.3)e
8100 (2.0)
3400 (1.4)
5000 (1.7)
4000 (3.1)
2200 (1.7)e
1900 (2.0)e
15500 (2.4)
9600 (2.6)
9900
8260
2750
7570
9640
33050
4850
4310
5357
1690
803
4.1
7.5
7
2
3d
4
5.2
11.8
23.4f
27f
5
6
7
8
9
10
11
VCH (3)
propene (3)
1-hexene (1)
1-hexene (2)
1-hexene (3)
MVK (1)
4
15
15
15
16
16
47f
53f
4.9
7.7
MVK (1)
a Conditions: complex 1, 0.005 g (8.30 × 10-6 mol); BPh3, 0.004 g (1.66 × 10-5 mol); CH2Cl2, 5 mL; 80 °C. b By GPC analysis in
1,2-dichlorobenzene at 135 °C using polystyrene standards. c By 1H NMR spectroscopy in 1,1,2,2-tetrachloroethane-d2 at 110 °C. d In the presence of 1
equiv of galvinoxyl. e By GPC analysis in THF at 35 °C using polystyrene standards. f By 1H NMR spectroscopy in CDCl3.
splitting observed in the analogous (η3-crotyl)palladium species
previously reported.10 At ambient temperature, 2 was found to
slowly decompose to give styrene and palladium black. Fur-
thermore, addition of 100 psi of ethene to 2-d9 in dichlo-
romethane at ambient temperature produced polyethene with a
deuterated styrenic end group. The kinetics of styrene insertion
into 1 were studied under pseudo-first-order conditions by
following the disappearance of the resonance at 22.7 ppm in
the 31P NMR spectrum. The reaction is first order in styrene,
and the Eyring plot shows a ∆Hq value of 64.3(6) kJ/mol-1
and a ∆Sq value of -60(20) J/(mol K).
galvinoxyl with Pd-H species that can attenuate metal-centered
nonradical reactions.14,15
The solution copolymerizations of ethene with 4-acetoxysty-
rene, 4-vinylmethylbenzoate, and 4-fluorostyrene were also
performed (conditions: complex 1, 0.005 g (8.30 × 10-6 mol);
BPh3, 0.004 g (1.66 × 10-5 mol); functional styrene, 6.2 ×
10-3 mol; ethene, 100 psi; CH2Cl2, 10 mL; 80 °C). The catalytic
activities for the copolymerizations were 12 800, 16 500, and
16 100 g (mol of Pd)-1 h-1, and the comonomer incorporations
were 2.8, 6.7, and 4.5 mol %, respectively. The hydrolysis of
4-acetoxystyrene- and 4-vinylmethylbenzoate containing co-
polymers afforded materials bearing hydroxyl and carboxylic
acid functionalities, respectively (see the Supporting Informa-
tion).
The water contact angles for poly(ethene-co-functional sty-
rene) copolymers were measured for thin films coated on glass
slides. Poly(ethene-co-styrene) containing 4.1 mol % of styrene
exhibits an advancing contact angle of 101° and a receding
contact angle of 89°. The introduction of 4-acetoxystyrene and
4-vinylmethylbenzoate into the copolymer results in the contact
angle dropping to 92° (advancing) and 82° (receding). However,
the presence of 4-fluorostyrene results in a slight increase in
contact angle with obtained values for poly(ethene-co-4-
fluorostyrene) of 109° (advancing) and 96° (receding).
The results of copolymerization using compound 1 with BPh3
are summarized in Table 1. Increasing the amount of comono-
mer in the feed results in its higher incorporation into the
copolymer; however, the molecular weight is lowered. The
ethene/styrene copolymerization also proceeds in the presence
of 1 equiv of the radical trap galvinoxyl, thereby eliminating
the role of radicals in the copolymerization. The drop in activity
in the presence of the trap can be attributed to the reaction of
The copolymerization of ethene with other vinyl monomers
such as vinylcyclohexane (VCH), propene, 1-hexene, and methyl
vinyl ketone (MVK) were also performed (Table 1). These
(14) Sen, A.; Borkar, S. J. Organomet. Chem. 2007, 692, 3291–3299.
(15) Albeniz, A. C.; Espinet, P.; Lopez-Fernandez, R.; Sen, A. J. Am.
Chem. Soc. 2002, 124, 11278–11279.

Communications
Organometallics, Vol. 27, No. 14, 2008 3333
Figure 1. 13C{1H} NMR assignment for poly(ethene-co-styrene) copolymer in 1,1,2,2-tetrachloroethane-d2 at 110 °C. The chemical shifts
are assigned on the basis of literature values12,16 and are given in ppm.
Figure 2. 13C{1H} NMR assignment for poly(ethene-co-vinylcyclohexane) copolymer in 1,1,2,2-tetrachloroethane-d2 at 110 °C. The chemical
shifts are assigned on the basis of literature values17 and are given in ppm.
monomers do not readily undergo radical copolymerization.
Copolymerization of ethene with 1-hexene results in copolymers
with an unusually high incorporation of 1-hexene. Copolym-
erization with a feed ratio of 3 g of 1-hexene to 50 psi of ethene
resulted in material with ∼50 mol % of 1-hexene, as determined
by 1H NMR spectroscopy. The structures of all the copolymer
presence of ethene-ethene sequences, whereas resonances at
45, 36, and 28 ppm represent [-(Ph)CHCH2CH2CH2-] carbons
(left to right), respectively, and confirm the ethene-styrene
linkage.16 Further, the absence of resonances at 41 and 34-35
ppm demonstrates the absence of a styrene-styrene linkage and
also indicates the absence of amorphous polystyrene generated
by thermal radical polymerization. The end group analysis
performed on low-molecular-weight poly(ethene-co-styrene)
copolymer (entry 3, Table 1) shows three types of chain ends:
styrenic, vinyl, and alkyl (Figure 1). The percentage of the
styrenic chain ends is greater than for the other two end groups
and is formed by ꢀ-H elimination following styrene insertion.
The unsaturated carbons next to the aromatic ring show 13C
NMR resonances at 129 and 131 ppm and are assigned by high-
1
materials were confirmed by H and 13C NMR spectroscopy.
In the case of poly(ethene-co-styrene), the incorporation of the
styrene was calculated by comparing the integration of the five
aromatic protons of styrene with all the aliphatic protons
appearing between 0.9 and 1.9 ppm. The two resonances, a
doublet at 6.3 ppm and a multiplet at 6.6 ppm, suggest the
presence of PhCHdCHCH2- chain ends formed by styrene
insertion and subsequent ꢀ-H elimination. The formation of
poly(ethene-co-styrene) was further confirmed by 13C{1H} NMR
spectroscopy in 1,1,2,2-tetrachloroethane-d2 at 110 °C. Both 1H
and 13C NMR analysis revealed the formation of linear
copolymers. The 13C resonance at 28.6 ppm suggests the
(16) Arriola, D. J.; Bokota, M.; Campbell, R. E.; Klosin, J.; LaPointe,
R. E.; Redwine, O. D.; Shankar, R. B.; Timmers, F. J.; Abboud, K. A.
J. Am. Chem. Soc. 2007, 129, 7065–7076.

3334 Organometallics, Vol. 27, No. 14, 2008
Communications
temperature HMQC analysis. The alkyl chain ends are assigned
on the basis of literature values.12 The vinyl chain ends formed
by ꢀ-H elimination following ethene insertion occur to a much
lower extent than the styrenic end groups.
DSC analysis of poly(ethene-co-styrene) (4.3 mol % styrene)
showed a Tm value of 106 °C, which is 23 °C lower than for
the corresponding linear polyethene. The low Tm value can be
attributed to a drop in polyethene crystallinity due to incorpora-
tion of styrene units. The Tm values for poly(ethene-co-4-
acetoxystyrene) and poly(ethene-co-4-fluorostyrene) were 114
and 118 °C, respectively. Similarly, the DSC analysis of
poly(ethene-co-vinylcyclohexane) containing 5.2 mol % of
vinylcyclohexane shows a Tm value of 109 °C, whereas the
copolymer with 11.8 mol % vinylcyclohexane does not show a
Tm value but has a Tg value of -9 °C.
In addition to the copolymerization of ethene with polar
styrene derivatives, the unusual functionality tolerance of the
catalyst system was demonstrated by performing the aqueous
emulsion copolymerization of styrene with ethene. The emulsion
copolymerization was performed using 5 g of styrene and 200
psi of ethene (conditions: P∼SO3H ligand, 0.0065 g (1.61 ×
10-5 mol); Pd(DBA)2, 0.0078 g (1.35 × 10-5 mol); galvinoxyl,
0.01 g (2.37 × 10-5 mol); BPh3, 0.0072 g (2.96 × 10-5 mol);
2,6-di-tert-butylpyridine, 0.0056 g (2.96 × 10-5 mol); sodium
dodecylbenzenesulfonate, 0.9 g; 30 mL of water and 10 mL of
toluene; 90 °C; 4 h), giving 0.3 g of copolymer with 5.8 mol %
of styrene incorporation. The high-temperature GPC analysis
of the polymer shows a monomodal peak with a Mw value of
2500 and a PDI value of 1.5. Galvinoxyl and 2,6-di-tert-
butylpyridine were added to suppress radical and cationic
polymerizations, respectively, confirming that the obtained
copolymerwasformedbymetal-catalyzedinsertionpolymerization.
The 1H NMR spectrum of poly(ethene-co-vinylcyclohexane)
at 110 °C in 1,1,2,2-tetrachloroethane-d2 shows resonances at
5.1 and 5.5 ppm, suggesting C6H11CHdCHCH2- chain ends,
which were further confirmed by 13C NMR spectroscopy. The
incorporation of vinylcyclohexane was determined by comparing
cyclic CH protons from vinylcyclohexane with all other aliphatic
protons. The vinylcyclohexane content values determined by
13C NMR spectroscopy (2 s delay) are close to those calculated
by 1H NMR spectroscopy.17 Furthermore, the 13C NMR
resonances observed are in good agreement with literature values
and suggest the presence of only isolated vinylcyclohexane units.
Similar to the case for poly(ethene-co-styrene), poly(ethene-
co-vinylcyclohexane) also shows unsaturated and alkyl chain
ends (Figure 2). The predominant unsaturated end group arises
by ꢀ-H elimination following vinylcyclohexane insertion, and
its percentage increases with an increase in the amount of
vinylcyclohexane in the feed (entries 4 and 5, Table 1). The 1H
NMR spectra of both poly(ethene-co-propene) and poly(ethene-
co-1-hexene) show vinyl chain ends. The predominant 13C NMR
resonances for poly(ethene-co-1-hexene) (∼50 mol % 1-hexene)
correspond to those reported previously for the alternating
copolymer.18,19
The copolymerization of ethene with methyl vinyl ketone was
also performed (Table 1). The obtained molecular weights and
level of methyl vinyl ketone incorporation were similar to those
observed for poly(ethene-co-styrene).
Acknowledgment. This research was supported by the
U.S. Department of Energy, Office of Basic Energy Sciences.
Supporting Information Available: Text and figures giving
experimental procedures and characterization data. This material
is available free of charge via the Internet at http://pubs.acs.org.
(17) Nomura, S.; Itagaki, K. Macromolecules 2005, 38, 8121–8123.
(18) Uozumi, T.; Ahn, C. H.; Tomisaka, M.; Jin, J.; Tian, G.; Sano, T.;
Soga, K. Macromol. Chem. Phys. 2000, 201, 1748–1752.
(19) Choo, T. N.; Waymouth, R. M. J. Am. Chem. Soc. 2002, 124, 4188–
4189.
OM800237R