A R T I C L E S
Ru¨nzi et al.
in acrylate homooligomerization.12 Copolymerization of ethyl-
ene with CO can occur in a non-alternating fashion,20 and
alternating copolymers of CO with methyl acrylate and vinyl
acetate have been reported.21
Table 1. Polymerization of Ethylene in the Presence of Methyl
Methacrylate and Methyl Isobutyratea
concn of additive
[mol/L]
TOF [mol (C2H4)
mol (Pd)-1 h-1
entry
yield [g]
]
Mw/Mnb
Mnb[g mol-1
]
1-1
1-2
1-3
1-4
1-5
1-6
1-7
-
3.14
2.74
1.60
0.83
0.32
3.17
2.17
9.0 × 104
7.8 × 104
4.6 × 104
2.4 × 104
0.9 × 104
9.1 × 104
6.2 × 104
2.1
2.4
2.2
1.9
n.m.
2.1
2.1
1.8 × 104
1.5 × 104
1.6 × 104
1.8 × 104
n.m.
Curiously, in view of the aforementioned scope of vinyl
monomers studied, little information exists on the behavior of
methacrylatessone of the largest volume vinyl monomerssin
such insertion polymerizations. Stoichiometric reaction of a
cationic diimine complex with methyl methacrylate (MMA)
yielded the isolable cationic chelate complex resulting from 1,2-
insertion.22 Polymerization of ethylene by neutral phosphineeno-
lato Ni(II) catalysts in the presence of MMA resulted in chain
termination upon MMA insertion, to yield enolate-terminated
polyethylenes.23 The nature of the products of ethylene polym-
erization with neutral Ni(II) salicylaldiminato complexes in the
presence of MMA is a topic of current interest.24 Otherwise,
little has been reported on the reactivity or lack thereof of
methacrylates in insertion polymerization. We now give a full
0.10 MMA
0.25 MMA
0.50 MMA
1.00 MMA
0.10 MIB
0.50 MIB
1.8 × 104
1.8 × 104
a 100 mL total volume (toluene), 2.5 µmol of 1-dmso (stock solution
in CH2Cl2), 5 bar ethylene pressure, 80 °C reaction temperature, 0.5 h
reaction time; 50 mg of radical inhibitor (galvinoxyl) was added. MMA,
methyl methacrylate; MIB, methyl isobutyrate. b Determined by GPC in
1,2,4-trichlorobenzene at 160 °C vs PE standards, n.m., not measured.
account of the reactivity toward methacrylates in insertion
polymerization catalyzed by neutral phosphinesulfonato Pd(II)
complexes.
Results and Discussion
(9) Borkar, S.; Newsham, D. K.; Sen, A. Organometallics 2008, 27, 3331–
3334.
Polymerization in the Presence of Methyl Methacrylate. For
polymerization studies, the dimethylsulfoxide-substituted
1-dmso12 was employed as a catalyst precursor. Due to the
lability of the dmso ligand, this catalyst precursor enables
polymerizations at low ethylene concentrations, and conse-
quently relatively high [comonomer] vs [ethylene], which can
favor comonomer incorporation. However, polymerizations in
the presence of variable concentrations of MMA (Table 1)
yielded ethylene homopolymer exclusively, as evidenced by
high-temperature 1H NMR and IR spectroscopic analysis of the
polymer formed (Figures S1-S5, Supporting Information).
Concerning the experimental accuracy of polymer analysis, in
ethylene-MA copolymers with 0.1 mol % acrylate incorpora-
tion, the latter could be clearly observed by NMR and IR
spectroscopy (Figures S6 and S7, Supporting Information).
Taking into account the molecular weights of the polyethylenes
formed (Table 1), the detection limit is less than one methacry-
late unit per chain. That is, also MMA-derived end groups can
be excluded. Indeed, only ethylene-derived vinyl and internal
olefinic end groups are observed by 1H NMR spectroscopy. By
comparison to the ethylene homopolymerization essentially
occurring in the presence of methacrylate, polymerization in
the presence of acrylate (MA) under conditions similar to those
of entry 1-4 (95 °C and 0.6 M methyl acrylate) resulted in the
formation of a copolymer with a substantial acrylate incorpora-
tion of 9.4 mol %. This corresponds to a preference for acrylate
vs methacrylate incorporation of at least 102.
While no incorporation was observed, increasing amounts of
MMA in the reaction mixture resulted in decreased polymeri-
zation productivities (entries 1-1 to 1-5).25 By comparison to
ethylene polymerization in the absence of MMA, no enhanced
loss of polymerization activity with polymerization reaction time
is evident (Table S1, Supporting Information). This suggests
that MMA is not primarily involved in an irreversible deactiva-
tion process. In polymerizations in the presence of the saturated
analogue of MMA, methyl isobutyrate (MIB), a similar lowering
of productivity with increasing MIB concentrations is observed
(entries 1-6 and 1-7), albeit the effect is less pronounced than
with MMA itself. Likely, coordination of the ester moiety to
(10) Skupov, K. M.; Marella, P. R.; Simard, M.; Yap, G. P. A.; Allen, N.;
Conner, D.; Goodall, B. L.; Claverie, J. P. Macromol. Rapid Commun.
2007, 28, 2033–2038.
(11) Vela, J.; Lief, G. R.; Shen, Z.; Jordan, R. F. Organometallics 2007,
26, 6624–6635.
(12) (a) Guironnet, D.; Roesle, P.; Ru¨nzi, T.; Go¨ttker-Schnetmann, I.;
Mecking, S. J. Am. Chem. Soc. 2009, 131, 422–423. (b) Guironnet,
D.; Caporaso, L.; Neuwald, B.; Go¨ttker-Schnetmann, I.; Cavallo, L.;
Mecking, S. J. Am. Chem. Soc. 2010, 132, 4418–4426.
(13) (a) Berkefeld, A.; Mecking, S. Angew. Chem., Int. Ed. 2008, 47, 2538–
2542. (b) Nakamura, A.; Ito, S.; Nozaki, K. Chem. ReV. 2009, 109,
5215–5244.
(14) Skupov, K. M.; Piche, L.; Claverie, J. P. Macromolecules 2008, 41,
2309–2310.
(15) Luo, S.; Vela, J.; Lief, G. R.; Jordan, R. F. J. Am. Chem. Soc. 2007,
129, 8946–8947.
(16) Weng, W.; Shen, Z.; Jordan, R. F. J. Am. Chem. Soc. 2007, 129,
15450–15451.
(17) Bouilhac, C.; Ru¨nzi, T; Mecking, S. Macromolecules 2010, 43, 3589–
3590.
(18) Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. J. Am. Chem. Soc.
2007, 129, 8948–8949.
(19) Ito, S.; Munakata, K.; Nakamura, A.; Nozaki, K. J. Am. Chem. Soc.
2009, 131, 14606–14607.
(20) (a) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I.
Chem. Commun. 2002, 964–965. (b) Hearley, A. K.; Nowack, R. J.;
Rieger, B. Organometallics 2005, 24, 2755–2763. (c) Haras, A.;
Michalak, A.; Rieger, B.; Ziegler, T. Organometallics 2006, 25, 946–
953.
(21) (a) Kochi, T.; Nakamura, A.; Ida, H.; Nozaki, K. J. Am. Chem. Soc.
2007, 129, 7770–7771. (b) Nakamura, A.; Munakata, K.; Kochi, T.;
Nozaki, K. J. Am. Chem. Soc. 2008, 130, 8128–8129.
(22) Borkar, S.; Yennawar, H.; Sen, A. Organometallics 2007, 26, 4711–
4714.
(23) Gibson, V. C.; Tomov, A. Chem. Commun. 2001, 1964–1965.
(24) The presence of methyl acrylate was reported to suppress any polymer
formation: (a) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Hwang,
S.; Grubbs, R. H.; Roberts, W. P.; Litzau, J. J. J. Polym. Sci. Part A
2002, 40, 2842–2854. Other studies report formation of (co)polymer
in the presence of acrylates or methacrylates, respectively: (b) Johnson,
L. K.; Bennett, A. M. A.; Dobbs, K. D.; Ionkin, A. S.; Ittel, S. D.;
Wang, Y.; Radzewich, C. E.; Wang, L. Patent WO 01/92347, 2001.
(c) Wang, L.; Hauptman, E.; Johnson, L. K.; McCord, E. F.; Wang,
Y.; Ittel, S. D. Patent WO 01/92342, 2001. (d) Shen, H.; Goodall,
B. L. U.S. Patent 2006/0270811, 2006. (e) Rodriguez, B. A.; Delferro,
M.; Marks, T. J. J. Am. Chem. Soc. 2009, 131, 5902–5919. However,
the distinct 13C NMR resonances of the methylene carbons adjacent
to a carbonyl group resulting from random acrylate or methacrylate
incorporation-CbH2CaH2CR(COOMe)CaH2CbH2-were not observed;
e.g., for methyl acrylate (R ) H), δ 32.4 (R), 27.4 (ꢀ), ref 7. For 13
C
NMR data of an ethylene/methyl methacrylate copolymer from acyclic
diene metathesis, cf.: (f) Schwendeman, J. E.; Wagener, K. B.
Macromolecules 2004, 37, 4031–4037.
(25) It is assumed that the solubility of ethylene does not differ significantly
for variable concentrations of toluene solutions of methyl methacrylate
and methyl isobutyrate.
9
16624 J. AM. CHEM. SOC. VOL. 132, NO. 46, 2010