Solid-state metathesis polycondensation

Article abstract of DOI:10.1021/ma0215924

Solid-state polycondensation near room temperature using acyclic diene metathesis (ADMET) chemistry was discussed. Solid-state ADMET polymerization promoted by two Grubbs catalysts were presented. The mild reaction conditions required for ADMET chemistry is enabled by the high volatility of ethylene, which is the small molecule released during polymerization. The process provides a route for the production of highly pure, high molecular weight polymers, and for the direct preparation of intractable polymers.

Full text of DOI:10.1021/ma0215924

Macromolecules 2003, 36, 539-542
539
Solid -Sta te Meta th esis P olycon d en sa tion
We now report that the olefin metathesis mechanism
can operate within these principles. Olefin metathesis
is a superb tool for making carbon-carbon connections
Ga r r ett W. Oa k ley, Step h en E. Leh m a n , J r .,
J a son A. Sm ith , P a u l va n Ger ven , a n d
Ken n eth B. Wa gen er *
7
in both organic and polymer chemistry, where the
important reactions of the day are ring-opening me-
8
The George & J osephine Butler Polymer Research
Laboratory, Department of Chemistry, University of Florida,
P.O. Box 117200, Gainesville, Florida 32611-7200
tathesis polymerization (ROMP), acyclic diene metath-
9
esis (ADMET) polymerization, ring-closing metathesis
10
11
(
RCM), and cross metathesis (CM). ADMET, RCM,
and CM all involve condensation steps, so in principle
all of them could operate in the solid state, assuming
some degree of amorphous character is present during
the conversion. Of the three, acyclic diene metathesis
chemistry leads to macromolecules, and in most ex-
amples, the small molecule released is ethylene. The
high volatility of ethylene explains why this solid-state
polycondensation can occur under such mild conditions.
All other known SSP examples release high boiling
condensates such as ethylene glycol (PET), water (ny-
lon), or phenol (polycarbonate). Low-temperature solid-
state polymerization can lead to the generation of highly
pure, high molecular weight polymers at or near room
temperature; further, the process may offer a new route
to the direct preparation of intractable polymers, which
presently are made via indirect techniques.
Received October 15, 2002
Revised Manuscript Received December 4, 2002
In tr od u ction . We report the first solid-state poly-
condensation of any kind to be done near room temper-
ature by using acyclic diene metathesis (ADMET)
chemistry. This equilibrium reaction is driven by the
elimination of the highly volatile condensate, ethylene,
which vents from the reacting solid to create high
polymer.
Solid-state polymerization (SSP) traditionally has
been divided into two classes: crystal-to-crystal polym-
1
erization and equilibrium condensation polymeriza-
tion.2 The principles governing these two types of
polymerization are quite different, for the former is
topological chemistry, while the latter occurs in the
amorphous state of semicrystalline polymers. Topologi-
1
,3
Key factors in any solid-state polycondensation are
the nature and the lifetime of the catalyst employed, in
this case, metathesis catalysts. Three of the most widely
used metathesis catalysts are bis(tricyclohexylphos-
phine) benzylidine ruthenium(IV) dichloride (1),12 tri-
cyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-
dihydroimidazol-2-ylidene] [benzylidine] ruthenium(IV)
cal SSP (the polymerization of diacetylenes and di-
4
olefins are examples) relies on a suitable arrangement
of the reactants in the monomer crystal to permit the
necessary contact between reacting groups with only the
slight vibrations allowed within a crystalline state. On
the other hand, significant molecular motions occur in
polycondensation SSP, mostly in the amorphous phase.
This motion facilitates the release of a small condensate
molecule (ethylene, in the case of ADMET chemistry),
which can be removed at the surface of the solid to drive
the increase in molecular weight.
1
3
dichloride (2), and 2,6-diisopropylphenylimidoneo-
phylidene molybdenum(VI) bis(hexafluoro-tert-butoxide)
1
4
(
3), commonly known as the first (1) and second (2)
generation Grubbs ruthenium catalysts and Schrock’s
molybdenum catalyst (3), respectively. Thus far, we
have shown that the two Grubbs catalysts promote
solid-state ADMET polymerization. Reported below are
the results of our research on this topic to date.
Solid-state polycondensation first was observed more
5
than 35 years ago and is practiced in the polyester,
polyamide, and polycarbonate industries. Polymeriza-
tion begins in the liquid (bulk) state at high tempera-
tures (usually above 250 °C), followed by cooling of the
macromolecule to a temperature below its semicrystal-
line melting point. The polymer chemistry then is
continued in the solid state above the glass transition
temperature, but below the melting point. Solid-state
polycondensations of this nature usually are done at
Exper im en tal Section . A typical experimental setup
is trivial and consists of equipping a three-neck round-
bottom flask with two vacuum adapters and a stopper.
The apparatus is evacuated, flame-dried, and purged
with argon; liquid monomer and catalyst are added at
constant temperature (( 2 °C) under a positive argon
pressure. Polymerization begins in the liquid state with
subsequent crystallization of the growing macromol-
ecule. This reactor then is left intact with argon flowing
over the semicrystalline solid, which is sampled periodi-
cally for molecular weight determination by gel perme-
ation chromatography (GPC) and/or NMR end group
analysis. Sampling consists of dissolving the solid in a
6
temperatures above 150 °C. This approach has distinct
advantages over performing the polymerization com-
pletely in the melt state, advantages which are found
both in terms of producing polymers of higher purity
(fewer side reactions occur at these lower temperatures)
and in the economics of the reaction (less energy is
required). The ADMET reaction has the potential of
operating in this manner, doing so at temperatures far
below 150 °C, even as low as room temperature.
Removal of the condensate is the rate-determining
factor in solid-state polycondensation, where greater
surface area within the polymerizing solid favors faster
evolution of the small molecule. The condensate can be
removed from the solid by using static or dynamic
vacuum or by exposure to a stream of inert gas. For
semicrystalline polymers, operating above Tg enhances
molecular translational mobility within the amorphous
regions, while the regions of crystallinity maintain the
shape of the particle during the polymerization.
“
quench” solution of ethyl vinyl ether (EVE), butylated
hydroxytoluene (BHT), and the GPC solvent to minimize
further reaction. Ethyl vinyl ether inhibits Grubbs
metathesis catalyst activity, and BHT is a free radical
scavenger. Reagents were purchased from Aldrich and
used as received unless noted otherwise. 1,9-Decadiene
1
5
1
2
13
was distilled over CaH before use. First and second
generation Grubbs catalysts were synthesized by known
methods. Syntheses of other monomers are discussed
herein.
Resu lts a n d Discu ssion . Figure 1 shows several
examples of ADMET solid-state polymerization. 1,9-
1
0.1021/ma0215924 CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/04/2003

5
40 Communications to the Editor
Macromolecules, Vol. 36, No. 3, 2003
F igu r e 1. A variety of monomers that undergo solid-state ADMET polymerization.
Ta ble 1. Resu lts of Solid -Sta te P olym er iza tion s of Mon om er 4 w ith P er iod ic Sa m p lin g
number-average mol wtsa at specified reaction times
catalyst
Mon:Cat. ratio
500:1
temp (°C)
30
3 h
6 h
12 h
24 h
48 h
72 h
96 h
168 h
1
2800
5400
2200
8900
3700
6400
5800
6600
7200
7000
9400
16000b
7800
9900
30000
7900
19000
30000
8800d
23000
20000
21000
4
5
31000c
2
500:1
30
4
5
12000
12000
15000
23000
27000
27000
a
Mn determined by GPC in chloroform verses polystyrene standards. b Actual time of sampling is 30 h. c Actual time of sampling is
d
1
07 h. Actual time of sampling is 119 h.
weights reported herein are well within the range
normally expected for equilibrium step polymerization
chemistry. For example, polyester, nylon, and polycar-
bonate all exhibit useful properties with number-aver-
1
6
age molecular weights of less than 25 000.
Both catalysts 1 and 2 promote ADMET solid-state
polymerization. First generation Grubbs is the more
active of the two, largely due to its higher reactivity at
lower temperatures, reaching number-average molec-
ular weights of 30 000 g/mol in 3 days at 45 °C. Second
generation Grubbs, 2, is slower but seems continue to
promote polymerization at later stages of the reaction.
This observation may be the result of the longer lifetime
of complex 2 as compared with the first generation
Grubbs complex, 1. The half-life of second generation
1
7
Grubbs is found to be 6 h at 55 °C in benzene
compared to 40 min for first generation Grubbs;18
however, we suspect that the lifetimes of these com-
plexes are longer in the solid state compared to those
in solution.
F igu r e 2. Gel permeation chromatography traces of the SSP
of 1,9-decadiene with first generation Grubbs at 45 °C sampled
periodically. The molecular weights listed at 3, 30, and 107 h
are number-average molecular weights based on polystyrene
equivalents.
When comparing polymerizations of the same catalyst
at different temperatures, higher temperatures achieved
higher molecular weights. For first generation Grubbs
at 30 °C, a number-average molecular weight of ap-
proximately 20 000 g/mol was achieved in 3 days, while
at 45 °C, it reached approximately 30 000 g/mol in the
same amount of time. A similar effect was found for
complex 2. At 30 °C, the number-average molecular
weight does not exceed 10 000 g/mol in 5 days, while
reaching approximately 27 000 g/mol at 45 °C in the
same amount of time.
Decadiene (4) was investigated first; all polymerizations
shown in Table 1 produced semicrystalline solids before
the first sampling was done.
These results demonstrate unequivocally that solid-
state polycondensation is occurring at temperatures as
low as 30 °C, with the possibility of the reaction
occurring at even lower temperatures. Figure 2 shows
the GPC traces for polymerizations done with first
generation Grubbs catalyst at 45 °C. As the polymeri-
zation proceeds, the number-average molecular weight
increases from 5400 to 31 000 g/mol, all while in the
solid state. It should be noted that all the molecular
Experiments also were conducted to increase the
surface area of the solid mixture in order to facilitate
escape of the condensate from the surface of the solid.
1,9-Decadiene (4) was polymerized in the melt with

Macromolecules, Vol. 36, No. 3, 2003
Communications to the Editor 541
F igu r e 3. ADMET mechanism at work in the amorphous region of a semicrystalline solid. Pathway A shows the diffusion of a
ruthenium carbene by interchange reactions without a net change in molecular weight. Pathway B illustrates an increase in
molecular weight by formation of ethylene. Pathway C illustrates how ethylene can migrate through a solid to the surface of the
material via the same mechanism.
second generation Grubbs at 70 °C for 10 min and then
quickly crystallized by cooling to room temperature. The
resulting low molecular weight semicrystalline polymer
effect on this molecular mobility. At 75 °C, an almost
negligible amount of solid-state polymerization occurs
with macromonomer 12 over a 2 week period, whereas
at 90 °C the number-average molecular weight doubles
in 24 h.
(Mn ) 1300 g/mol by NMR) was ground into a fine
powder with a chilled mortar and pestle. This finely
divided solid was brought to 45 °C and sampled over
time as before, showing that Mn steadily increases over
the course of a week, reaching 22 500 g/mol by NMR.
This represents an approximate 20-fold increase in
molecular weight, all while in the solid state.
Semicrystalline condensation polymers are thought
to undergo solid-state polymerization due to this en-
hanced mobility, which exists within the amorphous
region when above the glass transition temperature.
While physical diffusion of ethylene within the solid is
undoubtedly occurring, the situation is more complex
than just that. The increase in molecular weight cannot
be rationalized by diffusion of ethylene alone since the
motions of amorphous chain segments in semicrystalline
polymers are restrained by being anchored in the
Other monomers also are amenable to solid-state
metathesis polymerization. The ketone-functionalized
dienes, tricosa-1,22-dien-12-one (6) and heneicosa-1,20-
dien-11-one (7),19 as well as an alcohol-functionalized
2
0
diene, tricosa-1,22-dien-12-ol (10), react in a manner
similar to 1,9-decadiene. For example, second generation
Grubbs was mixed with the ketone-functionalized mono-
mer 7 at 115 °C for 10 min and then allowed to cool to
the solid state. The resulting polymer (4100 g/mol by
GPC) was ground into a fine powder and then placed
in a reaction flask at 80 °C. After 24 h, the molecular
weight had approximately doubled with an Mn of 8300
g/mol.
2
2
crystalline regions. A more recent model suggests that
migration of functionality can be explained by inter-
change reactions, a phenomenon termed “functional
group diffusion” which has been described by Abhira-
2
2
23
man et al. and Lenz and Schuler. We believe
functional group diffusion complements the physical
diffusion of ethylene.
Figure 3 illustrates how solid-state functional group
diffusion operates in the case of metathesis polyconden-
sation chemistry. Pathway A shows how the ruthenium
carbene migrates within the polymer sample simply as
a result of metathesis interchange reactions, which are
congruent with the proposed mechanism for ADMET.24
Reactions of this type do not lead to an increase in
molecular weight, but rather to chain length redistribu-
tion that results in a most probable molecular weight
distribution (Mw/Mn ) 2.0). Nevertheless, functional
groups are “diffusing” through the solid, which assists
end group encounters. Pathway B shows how ethylene
is generated, thereby increasing molecular weight.
Transport of ethylene to the surface of the solid is also
Other polymer architectures operate in the solid state
in a similar manner. For example, macromonomer 12
(
Mn ) 6700 g/mol) was synthesized via atom transfer
21
radical polymerization (ATRP) to create an amorphous
graft” of polystyrene at the center of a long-chain diene
“
monomer. This macromonomer undergoes ADMET solid-
state polymerization at 90 °C when combined with an
appropriate metathesis catalyst, achieving an Mn of
1
2 700 g/mol over 24 h. This reaction occurs despite the
large polystyrene branch attached to the diene. With
only two olefins per macromonomer, it is significant that
sufficient molecular mobility exists in the solid state to
allow polycondensation metathesis chemistry to occur.
In fact, even small changes in temperature have a large

5
42 Communications to the Editor
Macromolecules, Vol. 36, No. 3, 2003
aided by the same mechanism, as illustrated in pathway
C.
M.; Blechert, S. Angew. Chem., Int. Ed. Engl. 1997, 36,
2
037-2056. (e) Mol, J . C. Olefin Metathesis. In Fine
Chemicals through Heterogeneous Catalysis; Wiley: Wein-
heim, 2001. (f) F u¨ rstner, A. Angew. Chem., Int. Ed. 2000,
The opportunities afforded by solid-state metathesis
polycondensation are evident, for it could offer a syn-
thetic pathway to a variety of intractable polymer
structures. Many such polymers either have not been
made or are synthesized via indirect routes, usually via
a soluble precursor macromolecule. A direct solid-state
synthesis of such polymers has the potential of generat-
ing very pure materials. For example, the synthesis of
pure poly(phenylenevinylene) may be possible; other
intractable, and therefore inaccessible, conjugated poly-
mers may become feasible as well. In addition, solid-
state polycondensation may also be useful in ring-
closing metathesis and/or cross metathesis. These
opportunities are now under investigation.
3
9, 3012-3043.
(8) (a) Schrock, R. R. Acc. Chem. Res. 1990, 23, 158-165. (b)
Schrock, R. R. Ring Opening Metathesis Polymerization. In
Ring Opening Polymerization; Bruneile, D. J ., Ed.; Hanser:
Munich, 1993; pp 129-156. (c) Grubbs, R. H.; Khosravi, E.
Ring Opening Metathesis Polymerization (ROMP) and
Related Processess. In Synthesis of Polymers; Schluter, A.
D., Ed.; Materials Science and Technology Series; Wiley:
Weinheim, 1999; pp 65-104.
(
9) (a) Tindall, D.; Pawlow, J . H.; Wagener, K. B. Recent
Advances in ADMET Chemistry. In Alkene Metathesis in
Organic Synthesis; F u¨ rstner, A., Ed.; Topics in Organome-
tallic Chemistry Series; Springer: Berlin, 1998; pp 183-
1
98. (b) Davidson, T. A.; Wagener, K. B. Acyclic Diene
Metathesis (ADMET) Polymerization. In Synthesis of Poly-
mers; Schluter, A. D., Ed.; Materials Science and Technology
Series; Wiley: Weinheim, 1999; pp 105-122.
Ack n ow led gm en t. We thank the National Science
Foundation for financial support, the Army Research
Office for catalyst preparations, and Mr. Wendell Bobb
for his assistance with the 1,9-decadiene experiments.
We also thank Professor Dr. Gerhard Wegner, Max
Planck Institute Fur Polymerforschung, and Professor
A. S. Abhiraman, Georgia Institute of Technology, for
their helpful comments. We also thank Mr. Pat O’Donnell
for providing macromonomer 12.
(
10) (a) Grubbs, R. H.; Miller, S. J .; Fu, G. C. Acc. Chem. Res.
1995, 28, 446-452. (b) Grubbs, R. H.; Chang, S. Tetrahedron
1
998, 54, 4413-4450. (c) Hoveyda, A. H. Catalytic Ring-
Closing Metathesis and the Development of Enantioselective
Processes. In Alkene Metathesis in Organic Synthesis;
F u¨ rstner, A., Ed.; Topics in Organometallic Chemistry
Series; Springer: Berlin, 1998; pp 103-132.
(11) (a) Randall, M. L.; Snapper, M. L. J . Mol. Catal. A: Chem.
1
998, 133, 29-44. (b) Gibson, S. E.; Keen, S. P. Cross-
Metathesis. In Alkene Metathesis in Organic Synthesis;
F u¨ rstner, A., Ed.; Topics in Organometallic Chemistry
Series; Springer: Berlin, 1998; pp 155-181.
Refer en ces a n d Notes
(12) Schwab, P.; France, M. B.; Ziller, J . W.; Grubbs, R. H.
Angew. Chem., Int. Ed. Engl. 1995, 34, 2039-2041.
(
1) (a) Mrinal, T. Encyclopedia of Polymer Science and Engi-
neering; Wiley: New York, 1989; Vol. 15, pp 362-380. (b)
Wegner, G. Faraday Discuss. R. Chem. Soc. 1979, 68, 494-
(
13) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett.
999, 1, 953-956.
1
(
14) (a) Schaveria, C. J .; Dewan, J . C.; Schrock, R. R. J . Am.
Chem. Soc. 1986, 108, 2771. (b) Murdzek, J . S.; Schrock, R.
R. Organometallics 1987, 6, 1373-1374.
5
08.
(
2) (a) Pilati, F. Comprehensive Polymer Science; Pergamon:
New York, 1989; Vol. 5, pp 201-216. (b) Herzberg, O.; Epple,
M. Eur. J . Inorg. Chem. 2001, 1395-1406.
(
15) (a) Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J . Am. Chem.
Soc. 1997, 119, 3887-3897. (b) Sanford, M. S.; Ulman, M.;
Grubbs, R. H. J . Am. Chem. Soc. 2001, 123, 749-750. (c)
Louie, J .; Grubbs, R. H. Organometallics 2002, 21, 2153-
(
3) Bloor, D. Comprehensive Polymer Science; Pergamon: New
York, 1989; Vol. 5, pp 233-249.
(
4) (a) Hasegawa, M. Chem. Rev. 1983, 83, 507-518. (b)
Hasegawa, M. Comprehensive Polymer Science; Pergamon:
New York, 1989; Vol. 5, pp 217-232.
2
164.
16) Ravindranath, K.; Mashelkar, R. A. Chem. Eng. Sci. 1986,
1, 2197-2214.
(
4
(5) (a) Morosoff, N.; Lim, D.; Morawetz, H. J . Am. Chem. Soc.
(
(
17) Ulman, M.; Grubbs, R. H. J . Org. Chem. 1999, 64, 7202.
18) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett.
1
964, 86, 3167. (b) Macchi, E. M.; Morosoff, N.; Morawetz,
H. J . Polym. Sci., Part A-1 1968, 6, 2033-2049. (c) Chen,
1
999, 1, 953.
F. C.; Griskey, R. G.; Beyer, G. H. AIChE J . 1969, 15, 680-
6
85. (d) Chang, T. M. Polym. Eng. Sci. 1970, 10, 364-368.
(19) Zantour, H.; Pousse, A.; Mathilde, B. Bull. Soc. Chim. Fr.
1972, 12, 4715.
(20) Watson, M. D.; Wagener, K. B. Macromolecules 2000, 33,
5411-5417.
(21) O’Donnell, P. M.; Brzezinska, K.; Powell, D.; Wagener, K.
B. Macromolecules 2001, 34, 6845-6849.
(22) Srinivasan, R.; Almonacil, C.; Narayan, S.; Desai, P.;
Abhiraman, A. S. Macromolecules 1998, 31, 6813.
(23) Fitzgerald, J . A.; Irwin, R. S.; Memeger, W. Macromolecules
1991, 24, 3291.
24) (a) Wagener, K. B.; Boncella, J . M.; Nel, J . G. Macromol-
ecules 1991, 24, 2649-2657. (b) Lehman, S. E., J r.; Wagener,
K. B. Macromolecules 2002, 35, 48-53.
(
6) A recent exception has been reported by DeSimone and
Kiserow, who used supercritical CO2 as a plasicizer and
sweep fluid for synthesis of polycarbonate, thereby promot-
ing SSP as low as 90 °C. (a) Gross, S. M.; Roberts, G. W.;
Kiserow, D. J .; DeSimone, J . M. Macromolecules 2001, 34,
3
916-3920. (b) Shi, C.; DeSimone, J . M.; Kiserow, D. J .;
Roberts, G. W. Macromolecules 2001, 34, 7744-7750.
7) (a) Alkene Metathesis in Organic Synthesis; F u¨ rstner, A.,
Ed.; Topics in Organometallic Chemistry; Springer: Berlin,
(
1
998. (b) Ivin, K. J .; Mol, J . C. Olefin Metathesis and
Metathesis Polymerizations; Academic Press: New York,
997. (c) Metathesis Polymerization of Olefins and Polymer-
(
1
izations of Alkynes; Imamoglu, Y., Ed.; NATA ASI Series;
Kluwer Academic Publishers: Boston, 1998. (d) Schuster,
MA0215924