Photoinitiated Ring-Opening Metathesis Polymerization

Full text of DOI:10.1002/pola.29449

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Photoinitiated Ring-Opening Metathesis Polymerization
Wontae Joo,1 Christopher H. Chen,1 Jonathan P. Moerdyk,1 Ryan P. Deschner,2
1,2
Christopher W. Bielawski
,
3,4 Carlton Grant Willson
1Department of Chemistry, University of Texas at Austin, Austin, Texas 78712
2Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712
3Center for Multidimensional Carbon Materials (CMCM), Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
4Department of Chemistry and Department of Energy Engineering, Ulsan National Institute of Science and Technology (UNIST, Ulsan
44919, Republic of Korea
Correspondence to: C. G. Willson (E-mail: willson@che.utexas.edu)
Received 10 June 2019; Revised 17 July 2019; accepted 18 July 2019
DOI: 10.1002/pola.29449
KEYWORDS: dicyclopentadiene; lithography; photoacid generator; photochemistry; ROMP
displayed by acetylacetonate-supported Ru complexes (e.g., AG2).
The proposed mechanism entails a protonation event that facili-
tates ligand dissociation and ultimately, generation of a catalyti-
cally active species.
INTRODUCTION Ring-opening metathesis polymerization
(ROMP) is a valuable technique for converting strained cyclic ole-
fins to their respective polyalkenamers.1 Although myriad ROMP
catalysts are commercially available or readily accessible,2 addi-
tional structural modification is often required to achieve some
specific outcomes.3 For example, most ROMP reactions are initi-
ated by combining a monomer with a catalyst; however, some
applications, such as those that utilize photoresists, benefit from
an ability to store the two components for extended periods of
time.4 Such demands may be met through the use of latent cata-
lysts that remain in dormant states until activation is required.5
Various types of stimuli, including heat and light, have been used
to activate latent catalysts.6
To test our hypothesis, efforts were directed toward the synthe-
sis and study of SG2. Although SG2 is known,7b) the preparation
of this catalyst as well as many of the other bidentate systems
described above, require the use of thallium salts, primarily to
facilitate removal of chloride from requisite precursors. We dis-
covered that treatment of 2-[(mesitylimino)methyl]phenol with
sodium bis(trimethylsilyl)amide (NaHMDS) followed by G2
afforded the targeted catalyst in >80% overall yield (Scheme 1).
The nuclear magnetic resonance (NMR) and mass spectroscopic
data recorded for SG2 agreed with literature values,7b) and its
solid-state structure was independently elucidated using X-ray
crystallography (Fig. 1).
ROMP catalysts can be equipped with latency features through
the incorporation of bidentate ligands.7 For example, Verpoort
et al. reported a series of catalysts (e.g., SG2) that featured sal-
icylaldimines integrated into second generation Grubbs-type scaf-
folds (G2) (see 1).5a),7b)–d),8 While these catalysts are inactive
at room temperature,9 reactivity was observed at 90 ꢀC.7b) Fur-
ther structural modifications enabled refinement of the latency
characteristics and analogues were found that undergo activation
upon the introduction of Lewis or Bronsted acids.7e)–g)
Upon the synthesis and characterization of SG2, subsequent
efforts were directed toward exploring the activity of the catalyst.
Cyclooctadiene (COD) was selected as a model substrate and a
variety of experimental conditions, including the use of different
acids and intermittent exposure periods to UV light, were
explored (see Scheme 2 and Table 1). The reactions were moni-
tored by NMR spectroscopy by comparing the ratio of monomer
to polymer over time. Representative data are shown in Figure 2.
We reasoned that ROMP catalysts supported by salicylaldimines
may also undergo activation in the presence of a photoacid gener-
ator (PAG).10 Our hypothesis was inspired by a Grubbs’ report,11
which showed that the acids formed upon exposure of certain
PAGs to ultraviolet (UV) light enhanced the performance
In accordance with literature reports,7a),b) SG2 was found to be
relatively inactive and did not promote the ROMP of COD at room
Additional supporting information may be found in the online version of this article.
Current Addresses: W. Joo, Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139;
C. H. Chen, Zeon Specialty Materials Inc., San Jose, CA 95110; J. P. Moerdyk, Department of Chemistry, Seton Hill University, Green-
sburg, PA 15601; R. P. Deschner, NanoHybrids, Inc., Austin, TX 78744.
© 2019 Wiley Periodicals, Inc.
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SCHEME 2 ROMP of COD.
(1), was added in lieu of HCl and the resulting mixture was irradi-
ated with UV light. A series of control experiments revealed that
the PAG must be used in conjunction with UV light to activate
SG2. Although PAG-activated ROMP reactions were slower that
an analogous experiment conducted with HCl, presumably due to
constraints imposed by the photolysis kinetics, the result
supported our hypothesis and prompted us to further explore the
chemistry.
CHART 1 Structures of ROMP catalysts.
SCHEME 1 Synthesis of SG2.
To optimize the performance of the photoinitiated ROMP reac-
tion, other PAGs were tested and the additive stoichiometry was
systematically varied (see Table 1 and Fig. S3). Although modest
enhancements were observed when various triphenylsulfonium
salts were used (see Supporting Information for data and struc-
tures), these PAGs exhibit low solubilities in organic solvents.
Optimal results were obtained with 2-(4-methoxystyryl)-4,6-bis
(trichloromethyl)-1,3,5-triazine (2),12 which afforded faster
ROMP kinetics when compared to reactions that were performed
with N-hydroxynaphthalimide triflate (1). Increasing the PAG-to-
catalyst ratio beyond a molar equivalent did not significantly
enhance the rates of the light-activated ROMP reactions.
temperature. However, the addition of a molar equivalent (with
respect to catalyst) of HCl to the reaction mixture resulted in a
significant enhancement in catalytic activity. Inspection of the
data revealed that the performance displayed by SG2 upon activa-
tion with an acid was comparable to that of G2. An enhancement
was also observed when a PAG, N-hydroxynaphthalimide triflate
The ability to activate ROMP reactions using PAGs enabled tem-
poral control. The rates of the polymerization reactions were
TABLE 1 Summary of Reaction Conditions that Were Screened
for the ROMP of CODa
Entry
Catalyst
Additiveb
Lightc
Conv. (%)d
1
G2
–
–
>99
<1
2
SG2
SG2
SG2
SG2
SG2
SG2
SG2
–
–
–
3
HCle
PAG 1f
PAG 1f
–
–
>99
4
–
<1
5
UV
UV
–
49g
<1
6
7
PAG 2h
PAG 2h
PAG 2h
–
<1
52g
8
UV
UV
UV
9
<1
10
–
<1
a Conditions: [COD]0 = 500 mM; [G2 or SG2]0 = 5 mM; C6D6; room
temperature.
b One molar equivalent of HCl or PAG with respect to the catalyst
was used.
FIGURE 1 A representation of the solid-state structure of SG2.
The ellipsoids are drawn at the 50% probability level. Solvent
molecules and H atoms are omitted for clarity. Selected distances
(Å) and angles (ꢀ): Ru2-C66 1.811 (8), Ru2-C45 2.033 (7), Ru2-O2
2.040 (4), Ru2-N6 2.115 (6), Ru2-Cl2 2.3850 (18); N5-C45-Ru2 132.0
(5), C67-C66-Ru2 136.7 (6), C75-O2-Ru2 127.7 (4), C73-N6-Ru2 122.5
(5). [Color figure can be viewed at wileyonlinelibrary.com]
c The ROMP reaction was performed in the dark (−) or under UV light.
d Percent conversion of monomer to polymer after 15 min of reaction
time, as determined using NMR spectroscopy (see Fig. 2).
e A 1.0 M solution of HCl in diethyl ether was used.
f PAG 1 = N-hydroxynaphthalimide triflate.
g >99% conversion was achieved after 40 min.
h PAG 2 = 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine.
2
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FIGURE 2 Plots of the percentage of COD that was converted
to polymer versus time. Conditions: [COD]0 = 0.50 M,
[COD]0/[catalyst]0 = 100, [catalyst]0/[acid]0 = 1, C6D6, room
temperature. PAG 1 = N-hydroxynaphthalimide triflate, PAG
2 = 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine.
The entries indicated in the legend refer to Table 1. [Color
figure can be viewed at wileyonlinelibrary.com]
relatively slow in the dark and fast under UV light. The rate dif-
ferential was modulated over multiple cycles [Fig. 3(a)] and was
held in either state for prolonged periods [Fig. 3(b)] by intermit-
tently exposing the reaction vessel to UV light. Removal of the
reaction vessel from the source of UV light reduced the rate of
conversion of monomer to polymer, which is a counterintuitive
observation. We presume that this is due to the limited lifetimes
of the catalytically active intermediates. Behavior of this sort has
recently been reported for redox activated ruthenium catalysts
when irradiated in the presence of certain oxidizing pyrylium
photocatalysts.13
Nanoimprint lithography (NIL) is a process that is capable of
transferring nanometer-sized patterns to various substrates.14
Compared to other lithography techniques, NIL does not
require complex light sources or materials that are tailored to
specific wavelengths.15 Rather, the process utilizes low viscos-
ity imprint resists that are cured, usually with UV light, after
being shaped with a template.16 Although a variety of thermo-
plastics and thermosets have been used as resists in NIL
applications,17 new materials that effectively transfer patterns
with minimal defects are intensely pursued18 in part to obvi-
ate sophisticated fabrication processing steps used in the
semiconductor industry.19 A relatively unexplored class of
polymers for such purposes are those that are derived from
olefin metathesis.
FIGURE 3 Plots of the percentage of COD converted to polymer
versus time. (a) A reaction mixture was alternately exposed to UV
light and held in the dark for 10-min intervals (data in red). A
separate experiment in which the reaction mixture was irradiated
for the duration of the polymerization reaction is also shown (data
in black). (b) A reaction mixture was alternately exposed to UV light
and dark for prolonged periods of time. The label “Off” refers to a
period during which the light source was removed. Conditions:
[COD]0 = 0.50 M, [COD]0/[SG2]0 = 100, [SG2]0/[PAG]0 = 1, C6D6.
PAG = 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (2).
[Color figure can be viewed at wileyonlinelibrary.com]
Since crosslinking often reduces solubility and thus challenges
conventional, solution-based characterization techniques,
rheometry was used to monitor reaction progress. A C6D6
solution of DCPD ([DCPD]0 = 0.5 M), SG2 (0.1 mol %), and
PAG 2 (0.1 mol %) was casted onto a quartz disc and then
strain was measured by applying torque under UV light. The
point at which the reaction mixture became a crosslinked gel
was defined by the time at which the elastic storage modulus
(G0) was equal to the viscous loss modulus (G00). As shown in
Efforts were directed toward using the PAG-activated catalyst
to polymerize other monomers. Dicyclopentadiene (DCPD)
was selected because it is relatively inexpensive, undergoes
crosslinking upon polymerization, and forms robust materials
with useful mechanical properties.20 The ROMP of DCPD has
also been used as the basis of reaction injection molding21
and other applications, and thus may benefit from availability
of latent catalysts.22
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Figure 4, the ROMP of DCPD using SG2 reached a gel point in
approximately 13 min. In agreement with the polymerization
kinetics described above, a similar reaction performed with
HCl (in lieu of the PAG) was relatively fast and reached a gel
point within a few seconds.
Finally, the potential of using the PAG-activated catalyst in
NIL applications was explored. A freshly prepared mixture of
DCPD, SG2, and PAG 2 was casted onto a clean silicon wafer.
The surface of a quartz imprint template was treated with
tridecafluoro-1,1,2,2-tetrahydrooctyl dimethylchlorosilane to
facilitate release after curing. The imprint template was then
applied to the coated silicon wafer and irradiated with
365 nm UV light (Fig. S4). After the curing process was com-
plete, the template was removed and the transferred pattern
was analyzed by optical microscopy, atomic force microscopy
(AFM), and scanning electron microscopy (SEM).
FIGURE 5 An SEM image of the imprinted polymer as recorded
As shown in Figure 5, the square-shaped features of the template
were successfully transferred using the aforementioned method-
ology. According to the AFM data, wells with dimensions of up to
146 nm deep and 1.72 μm wide were measured (Fig. S5). Sam-
ples with line width resolutions as low as 950 nm were also pro-
duced (Fig. S6). For comparison, 30 μm resolution was reported
for other ROMP-based photolithography methods.23
at 45ꢀ after coating with Pt/Pd.
described herein can be expected to facilitate applications in con-
temporary imprint technology and other lithography applications,
particularly those that require latent or “on-demand” activation.
EXPERIMENTAL
In conclusion, a latent ROMP catalyst supported by a sal-
icylaldimine-based ligand was successfully prepared without the
use of thallium reagents. The catalyst was found to be inactive at
ambient temperature but rapidly promoted polymerization reac-
tions upon exposure to various acids, including those produced by
PAGs. The latent catalyst was successfully incorporated into a NIL
resist formulation that was used to create patterns in a
crosslinked, polymeric matrix. These structures were known to be
excellent barriers to reactive-ion etching.24 Considering the broad
range of monomers that are amenable to ROMP,25 the results
2-[(Mesitylimino)methyl]phenol
A
mixture of salicylaldehyde (1 g, 8.19 mmol) and 2,4,6-
trimethylaniline (1.11 g, 8.19 mmol) was dissolved in absolute eth-
anol (20 mL). After the addition of a few drops of formic acid
(approximately 0.2 mL) and 4 Å molecular sieves, the mixture was
refluxed until the reaction was complete (17 h; as determined by
thin layer chromatography). The crude reaction mixture was fil-
tered, poured into water (20 mL), and extracted with ethyl acetate
(15 mL) three times. The organic layers were combined, washed
with brine (10 mL), dried over MgSO4, and evaporated under
reduced pressure. Purification using column chromatography
(media: silica gel; eluent: hexane/ethyl acetate 9:1 v/v; retention
factor: 0.50) afforded the desired product as a yellow oil (1.9 g,
99%). Spectral data are in accordance with literature values.26 1
H
NMR (400 MHz, CDCl3, δ): 13.2 (s, 1H), 8.32 (s, 1H), 7.41 (ddd,
J = 8.4, 7.3, 1.7 Hz, 1H), 7.34 (dd, J = 7.7, 1.7 Hz, 1H), 7.10–7.05
(m, 1H), 6.98–6.93 (m, 1H), 6.93–6.92 (m, 2H), 2.30 (s, 3H), 2.18
(d, J = 0.6 Hz, 6H); 13C NMR (100 MHz, CDCl3, δ): 166.7, 161.3,
145.7, 134.5, 133.1, 132.1, 129.0, 128.2, 118.9, 118.9, 117.3, 20.8,
18.5; high-resolution mass spectrometry (HRMS) (electrospray ion-
ization, m/z): [M − H]+ calcd for C16H16NO, 238.1230; found,
238.1237.
Salicylaldimine-Supported Second Generation Grubbs
Catalyst (SG2)
A round-bottom flask was charged with 2-[(mesitylimino)methyl]
phenol (538 mg, 2.25 mmol), NaHMDS (432 mg, 2.36 mmol),
dry tetrahydrofuran (7.5 mL), and a stir bar. Upon stirring
for 30 min, the solution was filtered through a 0.2 μm
poly(tetrafluoroethylene) filter into another flask that was
charged with G2 (1.91 g, 2.25 mmol) and a stir bar. After
heating the resulting solution to 60 ꢀC for 16 h, it was cooled to
FIGURE
4
Plots of moduli versus time. G0 = elastic storage
viscous loss modulus. Conditions: [DCPD]0
modulus, G00
=
= 0.50 M, [DCPD]0/[SG2]0 = 100, [SG2]0/[acid or PAG]0 = 1, C6D6.
PAG = 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (2).
[Color figure can be viewed at wileyonlinelibrary.com]
4
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S. Monsaert, R. Drozdzak, F. Verpoort, P. Van Der Voort, N. Ledoux,
B. Allaert, J. Organomet. Chem. 2006, 691, 5482. f) N. Ledoux,
R. Drozdzak, B. Allaert, A. Linden, P. Van Der Voort, F. Verpoort, Dalt.
Trans. 2007, 5201. g) A. M. Lozano Vila, S. Monsaert, R. Drozdzak,
S. Wolowiec, F. Verpoort, Adv. Synth. Catal. 2009, 351, 2689.
room temperature and poured into excess pentane. Filtration of
the precipitated solids afforded the desired product as a dark red
solid (950 mg, 82%). Spectral data are in accordance with litera-
ture values.7b) 1H NMR (400 MHz, CDCl3, δ): 18.64 (s, 1H), 7.59
(s, 1H), 7.44 (d, J = 7.8 Hz, 2H), 7.34–7.25 (m, 2H), 7.02–6.88 (m,
5H), 6.76–6.67 (m, 2H), 6.57 (s, 1H), 6.49 (m, 2H), 6.24 (s, 1H),
4.17–3.88 (m, 4H), 2.61 (s, 3H), 2.41 (s, 3H), 2.25–2.15 (m, 12H),
2.00 (s, 3H), 1.46 (s, 3H), 1.04 (s, 3H); 13C NMR (100 MHz, CDCl3,
δ): 297.4, 221.2, 169.4, 167.3, 164.3, 151.9, 150.0, 139.9, 139.0,
138.6, 137.8, 137.5, 137.0, 136.7, 136.5, 134.0, 133.9, 133.7, 131.6,
130.1, 129.3, 129.2, 129.0, 129.0, 128.3, 128.0, 127.9, 127.6, 123.3,
119.0, 113.4, 51.3, 50.8, 21.0, 20.9, 20.8, 20.0, 18.7, 18.2, 18.1,
17.7; HRMS (ESI, m/z): [M + Na]+ calcd for C44H48ClN3NaORu,
794.2433; found, 794.2419.
8 a) B. De Clercq, F. Verpoort, Adv. Synth. Catal. 2002, 344, 639.
b) M. Jordaan, H. C. M. Vosloo, Adv. Synth. Catal. 2007, 349, 184.
9 S. Chang, L. R. Jones, C. Wang, L. M. Henling, R. H. Grubbs,
Organometallics 1998, 17, 3460.
10 a) J. Wappel, R. C. Fischer, L. Cavallo, C. Slugovc, A. Poater,
Beilstein J. Org. Chem. 2016, 12, 154. b) B. Ö. Öztürk,
S. Karabulut S¸ehitoglu, M. A. R. Meier, Eur. Polym. J. 2015, 62,
116. c) B. Ö. Öztürk, E. Bucak, S. Karabulut, J. Mol. Catal. A
Chem. 2013, 376, 53. d) J. S. M. Samec, B. K. Keitz,
R. H. Grubbs, J. Organomet. Chem. 2010, 695, 1831.
11 B. K. Keitz, R. H. Grubbs, J. Am. Chem. Soc. 2009, 131, 2038.
12 a) G. Pohlers, J. C. Scaiano, R. Sinta, R. Brainard, D. Pai,
Chem. Mater. 1997, 9, 1353. b) G. Pohlers, J. C. Scaiano,
R. Sinta, Chem. Mater. 1997, 9, 3222.
ACKNOWLEDGMENTS
The Army Research Office (W911NF0910446) is acknowledged
for support. C. G. Willson acknowledges the Welch foundation
grant (F-1830). C. W. Bielawski acknowledges the Institute for
Basic Science (IBS-R019) as well as the BK21 Plus Program as
funded by the Ministry of Education and the National Research
Foundation of Korea. The authors are grateful to Vincent Lynch
(X-ray diffraction), Heonjoo Ha (rheometry), Angela Spangenberg
(nuclear magnetic resonance), and Philip Liu (scanning electron
microscopy) for their assistance with various experiments.
13 C. Theunissen, M. A. Ashley, T. Rovis, J. Am. Chem. Soc.
2019, 141, 6791.
14 a) S. Y. Chou, P. R. Krauss, P. J. Renstrom, Science 1996, 272,
85. b) S. Y. Chou, J. Vac. Sci. Technol. B 1996, 14, 4129.
15 a) W. L. Matthew, C. Traub, V. N. Truskett, Annu. Rev. Chem. Bio-
mol. Eng. 2016, 7, 583. b) H. Schift, J. Vac. Sci. Technol. B 2008, 26, 458.
16 E. A. Costner, M. W. Lin, W.-L. Jen, C. G. Willson, Annu. Rev.
Mater. Res. 2009, 39, 155.
17 a) F. Palmieri, J. Adams, B. Long, W. Heath, P. Tsiartas,
C. G. Willson, ACS Nano 2007, 1, 307. b) B. K. Long, B. K. Keitz,
C. G. Willson, J. Mater. Chem. 2007, 17, 3575. c) F. L. Palmieri,
M. D. Dickey, K. Wu, E. K. Kim, M. D. Stewart, J. G. Ekerdt,
C. G. Willson, J. Vac. Sci. Technol. B 2006, 23, 2967.
REFERENCES AND NOTES
1 a) N. Calderon, Acc. Chem. Res. 2005, 5, 127. b) M. R. Buchmeiser,
Chem. Rev. 2000, 100, 1565. c) G. C. Vougioukalakis, R. H. Grubbs,
Chem. Rev. 2010, 110, 1746. d) D. Astruc, New J. Chem. 2005, 29, 42.
e) S. Monfette, D. E. Fogg, Chem. Rev. 2009, 109, 3783. f) C. Slugovc,
Macromol. Rapid Commun. 2004, 25, 1283. g) C. W. Bielawski,
R. H. Grubbs, Prog. Polym. Sci. 2007, 32, 1.
18 a) S. Takei, T. Ogawa, R. Deschner, K. Jen, T. Nihira,
M. Hanabata, C. G. Willson, Jpn. J. Appl. Phys. 2010, 49,
0752011. b) R. Deschner, C. G. Willson, S. Takei, T. Ogawa,
M. Hanabata, Micro Nano Lett. 2010, 5, 117. c) S. Takei,
T. Ogawa, C. G. Willson, Micro Nano Lett. 2011, 6, 422.
2 a) B. Autenrieth, H. Jeong, W. P. Forrest, J. C. Axtell, A. Ota,
T. Lehr, M. R. Buchmeiser, R. R. Schrock, Macromolecules 2015,
48, 2480. b) B. K. Keitz, A. Fedorov, R. H. Grubbs, J. Am. Chem.
Soc. 2012, 134, 2040.
19 a) F. Palmieri, M. D. Stewart, J. Wetzel, J. Hao,
Y. Nishimura, K. Jen, C. Flannery, B. Li, H. -L. Chao, S. Young,
W. C. Kim, P. S. Ho, C. G. Willson, Proc. SPIE 2006, 6151, 6151.
b) F. Xu, N. A. Stacey, M. Watts, V. Truskett, I. McMackin, J. Choi,
P. Schumaker, E. Thompson, D. Babbs, S. V. Sreenivasan, C.
G. Willson, N. Schumaker, Proc. SPIE 2004, 5374, 232.
3 a) M. S. Sandford, J. A. Love, R. H. Grubbs, J. Am. Chem. Soc.
2001, 123, 6543. b) P. Schwab, M. B. France, J. W. Ziller,
R. H. Grubbs, Angew. Chem. Int. Ed. 1995, 34, 2039.
4 a) A. Ruiu, D. Sanna, V. Alzari, D. Nuvoli, A. Mariani, J. Polym.
Sci. Part A: Polym. Chem. 2014, 52, 2776. b) V. Alzari, D. Nuvoli,
D. Sanna, A. Ruiu, A. Mariani, J. Polym. Sci. Part A: Polym.
Chem. 2016, 54, 63. c) I. D. Robertson, E. L. Pruitt, J. S. Moore,
ACS Macro Lett. 2016, 5, 593.
20 a) T. A. Davidson, K. B. Wagener, J. Mol. Catal. A: Chem.
1998, 133, 67. b) J. Chen, F. P. Burns, M. G. Moffitt, J. E. Wulff,
ACS Omega 2016, 1, 532.
21 J. C. Mol, J. Mol. Catal. A: Chem. 2004, 213, 39.
22 a) S. J. P’Pool, H. J. Schanz, J. Am. Chem. Soc. 2007, 129, 14200.
b) I. D. Robertson, L. M. Dean, G. E. Rudebusch, N. R. Sottos,
S. R. White, J. S. Moore, ACS Macro Lett. 2017, 6, 609.
5 a) S. Monsaert, A. Lozano Vila, R. Drozdzak, P. Van Der Voort,
F. Verpoort, Chem. Soc. Rev. 2009, 38, 3360. b) C. Slugovc,
B. Perner, F. Stelzer, K. Mereiter, Organometallics 2004, 23, 3622.
c) A. Hejl, M. W. Day, R. H. Grubbs, Organometallics 2006, 25,
6149. d) P. A. van der Schaaf, A. Hafner, F. Rime, A. Mühlebach,
R. Kolly, H.-J. Kirner, J. Organomet. Chem. 2002, 606, 65.
23 R. A. Weitekamp, H. A. Atwater, R. H. Grubbs, J. Am. Chem.
Soc. 2013, 135, 16817.
24 R. R. Kunz, S. C. Palmateer, A. R. Forte, R. D. Allen, G. M. Wallraff,
R. A. Di Pietro, D. C. Hofer, Proc. SPIE 1996, 2724, 365.
6 a) A. J. Teator, C. W. Bielawski, J. Polym. Sci. Part A: Polym.
Chem. 2017, 55, 2949. b) A. J. Teator, D. N. Lastovickova,
C. W. Bielawski, Chem. Rev. 2016, 116, 1969.
25 a) H. V. Tran, R. J. Hung, T. Chiba, S. Yamada, T. Mrozek,
Y. T. Hsieh, C. R. Chambers, B. P. Osborn, B. C. Trinque,
M. J. Pinnow, S. A. MacDonald, C. G. Willson, D. P. Sanders,
E. F. Connor, R. H. Grubbs, W. Conley, Macromolecules 2002,
35, 6539. b) D. P. Sanders, S. A. MacDonald, C. G. Willson,
R. J. Hung, R. H. Grubbs, E. F. Connor, T. Chiba, B. P. Osborn,
W. Conley, Macromolecules 2003, 36, 1534.
7 a) S. Monsaert, N. Ledoux, R. Drozdzak, F. Verpoort, J. Polym. Sci.
Part A: Polym. Chem. 2010, 48, 302. b) B. Allaert, N. Dieltiens,
N. Ledoux, C. Vercaemst, P. Van Der Voort, C. V. Stevens, A. Linden,
F. Verpoort, J. Mol. Catal. A: Chem. 2006, 260, 221. c) B. De Clercq,
F. Verpoort, J. Mol. Catal. A: Chem. 2002, 180, 67. d) B. De Clercq,
F. Verpoort, Tetrahedron Lett. 2002, 43, 9101. e) D. Schaubroeck,
26 J. Yang, Dalt. Trans. 2017, 46, 5003.
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