Cross-linkable carbosilane polymers with imbedded disilacyclobutane rings derived by Acyclic Diene metathesis polymerization

Article abstract of DOI:10.1021/ma049760a

Cyclolinear carbosilane polymers with disilacyclobutane (DSCB) rings in the main-chain structure were prepared by means of acyclic diene metathesis (ADMET) polymerization of the corresponding 1,3-dibutenyl-1,3-disilacyclobutanes. The copolymerization of a

Full text of DOI:10.1021/ma049760a

Macromolecules 2004, 37, 5257-5264
5257
Cross-Linkable Carbosilane Polymers with Imbedded Disilacyclobutane
Rings Derived by Acyclic Diene Metathesis Polymerization
Zh izh on g Wu , J er r y P . P a p a n d r ea , Tom Ap p le, a n d Leon a r d V. In ter r a n te*
Department of Chemistry and Chemical Biology, New York State Center for Polymer Synthesis,
Rensselaer Polytechnic Institute, Troy, New York 12180-3590
Received February 4, 2004; Revised Manuscript Received May 12, 2004
ABSTRACT: Cyclolinear carbosilane polymers with disilacyclobutane (DSCB) rings in the main-chain
structure were prepared by means of acyclic diene metathesis (ADMET) polymerization of the corre-
sponding 1,3-dibutenyl-1,3-disilacyclobutanes. The copolymerization of a monomer of this type with a
noncyclic organosilane diene allowed for the incorporation of a varying number of DSCB rings into the
polymer backbone. Subsequent hydrogenation of the double bonds with p-toluenesulfonhydrazide resulted
in a saturated hydrocarbon structure in the main chain without affecting the DSCB ring. All of the
resultant polymers are well-defined materials with DSCB rings incorporated into the backbone structure,
as evidenced by NMR spectroscopy and GPC analyses. The thermal behavior of these polymers was
characterized by DSC and TGA. DSC indicated low Tgs, and TGA evidenced high thermal stability in an
inert atmosphere. In addition, large exothermic peaks were observed in the DSC, which indicated, along
with the IR and solid-state 29Si NMR spectra, that cross-linking occurs during heating to ca. 250 °C via
opening of the imbedded DSCB rings. The swelling properties of the resultant, thermally stable,
carbosilane network materials on exposure to various solvents were also examined.
In tr od u ction
often hard to remove and can change their properties;
they can also limit their potential application in such
fields as microelectronics and medicine. The use of the
disilacyclobutane (DSCB) ring as a means of thermoset-
ting polymers, however, has not been previously re-
ported. This is despite the fact that such rings are also
known to undergo thermally induced ROP to produce
polymers containing alternating silicon and carbon
atoms in the backbone, which have unique properties
such as good thermal and hydrolytic stability, low Tgs,
owing to a high chain flexibility, as well as serving as
high-yield precursors to SiC ceramics.17,18 Our recent
efforts have been directed toward the synthesis of
monomers that contain a reactive DSCB ring incorpo-
rated into the main chain of relatively high molecular
weight, linear, carbosilane polymers and copolymers.19
Such cyclolinear carbosilane polymers offer the prospect
of thermally induced cross-linking at moderate temper-
atures to afford elastomers and resins which possess the
excellent thermal stability characteristics of the base
carbosilane polymers.20
In the past few decades, cross-linkable polymers and
polymer composites have found a high demand in such
domains as interpenetrating polymer networks,1 organic
light-emitting materials,2,3 formation of thermally and
chemically resistant coatings and bulk materials,4 and
precursors to ceramic materials.5 Considerable effort
has been expended in order to introduce reactive
functionality into polymers, which will act as sites for
cross-linking reactions. Such built-in cross-linkable
functionality offers substantial advantages over alterna-
tive two-component mixtures or one-step formation of
cross-linked, network solids. Chain growth and cross-
linking reactions become independent of one another,
either expanding the materials application ranges or
improving the processability of thermally stable poly-
mers. Cross-linking reactions are also separated from
chain growth, providing complete control over the
chemical structure of the primary polymer and network
structures. In addition, the cross-linking agent is in-
corporated as a comonomer into the backbone of rela-
tively high molecular weight polymers, allowing the
cross-linking density to be directly related to the
monomer composition. Polymers with vinyl,6 siloxane,7
silane,8 and phosphazene9 backbones are some examples
of materials that have been synthesized with reactive
cross-linkable functionalities at the ends or on a side
chain.
High-temperature cross-linkable polymers and oligo-
mers containing reactive functionalities such as acety-
lene,10 benzocyclobutene,11 ethylene,12 and epoxide13
have been widely investigated. In recent years, the
thermally induced ring opening of pendant or end group
monosilacyclobutane rings has also been suggested as
a way to cross-link various kinds of polymers and
oligomers.14,15 The idea comes from the fact that the
four-membered silacyclobutane ring is susceptible to
ring-opening polymerization (ROP) without any catalyst
present.16 Residual catalysts in thermoset materials are
Acyclic diene metathesis polymerization (ADMET), a
relatively new route to olefin-containing organic poly-
mers that emerged in the late 1980s,21 offers a potential
approach to such cross-linkable, cyclolinear, carbosilane
polymers. The polymerization is typically carried out on
terminal diene monomers by using the highly selective
Shrock22 or Grubbs23 catalysts. The driving force for this
metathesis reaction is the removal of ethylene, resulting
in the formation of linear, olefin-containing, polymers.
This reaction allows the polymerization of many differ-
ent monomers with different functionality and produces
regular, well-defined, condensation polymers with unique
properties. Various silicon-containing polymers have
been prepared in this manner by Wagener and co-
workers during the past decade.24 However, no studies
have been reported involving diene monomers that
contain a di- or monosilacyclobutane group, which can
ring-open and subsequently cross-link on heating, to
10.1021/ma049760a CCC: $27.50 © 2004 American Chemical Society
Published on Web 06/18/2004

5258 Wu et al.
Macromolecules, Vol. 37, No. 14, 2004
Sch em e 1. Tw o Syn th etic Rou tes to Mon om er s 3a ,b
first by nucleophilic substitution of a dichlorosilane
(1a ,b) with a Grignard reagent to form an olefin-
substituted monochlorosilane, followed, after purifica-
tion, by reaction with magnesium to carry out the ring
closure reaction, thereby producing the olefin-substi-
tuted 1,3-disilacyclobutane four-membered ring. Ap-
proach 2 (Scheme 1) is the synthetic route developed in
this laboratory,27 which first employs an isopropoxy
group to facilitate the formation of the DSCB ring in
the “reverse Grignard” ring closure reaction. This iso-
propoxy intermediate was then converted to a more
reactive dichloro-substituted DSCB. In the last step the
diene-substituted DSCB was obtained by coupling with
butenylmagnesium bromide. Both of the two methods
provide similar overall yields of about 40%. However,
although approach 2 contains more steps, this approach
was preferred due to the relative ease in carrying out
the ring closure reaction, which is difficult to initiate
in the case of the first approach. These monomers were
obtained as liquids which contained two isomers (the
ratio of trans and cis was about 1:1 for the R ) Me
monomers and 6:4 for the R ) Ph monomers) as
produce heat-resistant, thermosetting materials. The
advantage of this cross-linking route is that the result-
ant network carbosilane materials could then be ob-
tained without added catalyst or cross-linker and with-
out evolution of volatiles. By controlling the cross-link
density and the polymer functionality, the resulting
materials could be used, for example, as thermally
stable elastomers, coatings, matrix resins for advanced
composites, and a source of SiCx ceramic fibers, ma-
trixes, or molded ceramic objects.
1
confirmed by H, 13C, and 29Si NMR and GC.
Hom op olym er Syn th eses. The unsaturated ho-
mopolymers 4a ,b were prepared by acyclic diene me-
tathesis (ADMET) polymerization of the corresponding
1,3-dibutenyl-1,3-disilacyclobutane monomer, as shown
in Scheme 2. It has already been reported that dienes
readily undergo ADMET polymerization in the presence
of the Shrock or Grubbs catalyst systems.22,23 In this
study, the Grubbs second-generation catalyst was em-
ployed.23 After polymerization and purification, the
polymers were obtained as clear, colorless viscous
materials, which were readily soluble in common sol-
vents such as hexane, THF, chloroform, and toluene.
The polymerization reaction proceeded cleanly with
almost complete conversion and with very little residual,
unreacted monomers remaining.
Resu lts a n d Discu ssion
Mon om er Syn th eses. 1,3-Diene-1,3-disilacyclobu-
tane monomers were prepared by using two approaches.
Approach 1 (Scheme 1) is analogous to that employed
for the synthesis of 1,1,3,3-tetramethyl-1,3-disilacy-
clobutane,25 roughly comprising the synthetic steps
employed by Auner for the synthesis of other substituted
1,3-disilacyclobutanes.26 The syntheses were carried out
Sch em e 2. Syn th etic Rou tes to Cyclolin ea r Ca r bosila n e P olym er s

Macromolecules, Vol. 37, No. 14, 2004
Cross-Linkable Carbosilane Polymers 5259
F igu r e 2. 29Si NMR spectra of monomer 3a (A), polymer 4a
(B), and the reduced polymer 5a (C).
dilute the disilacyclobutane ring on the main chain and
to determine the copolymerization efficiency. Polymer-
ization conditions were similar to the homopolymeriza-
tion of the monomer 3a . Fortunately, these conditions
were suitable for obtaining relatively high molecular
weight copolymers. Gel permeation chromatography
(GPC) in chloroform relative to narrow polystyrene
standards showed only one relatively sharp peak, which
indicates that homopolymer mixtures are not produced.
The incorporation of the disilacyclobutane rings into the
F igu r e 1. 1H NMR spectra of monomer 3a (A), polymer 4a
(B), and the reduced polymer 5a (C).
In the 1H NMR spectrum, the terminal olefinic
protons are clearly observed for the monomers but
completely disappear in the spectra of the polymers. The
resultant spectra indicated the occurrence of a conden-
sation polymerization, but not a ring-opening polymer-
ization, and also showed that relatively high molecular
weight polymers are formed. The 1H NMR peaks as-
signed to the disilacyclobutane methylene protons were
still observed in the same chemical shift range as the
monomer, except for signal broadening (Figure 1). This
indicates that the disilacyclobutane ring, which is very
sensitive to ring opening with various catalysts,28
survives the ADMET polymerization.
The silicon atoms of the disilacyclobutane ring in the
polymer are clearly observed as doublets in the 29Si
NMR spectra (Figure 2), suggesting that the cis and
trans isomers still exist in the ADMET polymer. The
internal olefinic carbons in the polymer are also easily
distinguished as trans and cis by 13C NMR spectroscopy,
with the cis-olefinic carbons appearing at 131.46 ppm
and the trans carbons appearing at 131.65 ppm (for
polymer 4a ).24 Thus, this is a very unusual linear
polymer with both the rings and olefins in the main
chain having trans and cis structures. The GPC analysis
of these polymers showed Mn values of 1.4 × 104
(polymer 4a ) and 1.1 × 104 (polymer 4b). The polydis-
persities were 1.9 and 2.1, respectively, which fit well
with the step-growth mechanism of the ADMET polym-
erization and provide further evidence that significant
cross-linking did not occur during polymerization.
1
polymer chains is confirmed by H, 13C, and 29Si NMR
spectra. In the 1H NMR spectra, a sharp peak was
observed at δ ) 0.24 ppm characteristic of the CH3
group attached to the disilacyclobutane ring. The ratio
of this resonance with respect to the resonance at δ )
0.42 ppm characteristic of the SiCH2CH2Si grouping
proved to be a reliable check of the copolymer compo-
sition, which showed that the incorporation of disila-
cyclobutane units matched the expected values fairly
well. Finally, neither the 1H, 13C, nor the 29Si NMR
spectra revealed any indication of chain microstructure
ordering in the copolymers, which we assume to be
random copolymers that are formed with no preferential
reactivity between the different monomers.
The initially obtained ADMET polymers and copoly-
mers were saturated by hydrogenation using the method
developed by Hahn,29 which does not require the use of
high-pressure H2. This method uses an in-situ generated
hydrogenating agent, diimide, obtained from toluene-
sulfonhydrazide by heating. To prevent the ring opening
of the disilacyclobutanes in the polymer at this stage,
the reaction temperature was decreased to 100-110 °C
instead of the refluxing conditions originally reported.29
1
Again, H NMR spectroscopy indicated that the disila-
cyclobutane rings survived this reduction reaction (Fig-
ure 1), and 29Si NMR indicated that the rings still had
trans and cis structures in a 1:1 ratio. These reactions
provided apparently 100% hydrogenation as evidenced
Cop olym er Syn th eses. As shown in Scheme 2, the
monomer 3a was copolymerized with the noncyclic
organosilane 1,2-bis(butenyldimethylsilyl)ethane 3c to

5260 Wu et al.
Macromolecules, Vol. 37, No. 14, 2004
Ta ble 1. P h ysica l P r op er ties of th e Red u ced Ca r bosila n e
P olym er s a n d Cop olym er s
∆H of reaction TGA (°C)
polymers Mw/Mn (10-3
)
Tg (°C)
(kJ /mol)
N2 (-5%)
5a
5b
5c
5d
5e
28.3/14.1
23.4/11.2
21.6/9.8
23.9/13.3
35.9/18.5
-65.0
-5.0
-65.2
-65.8
-62.7
-43.7
-38.3
-20.2
-4.9
0
470.3
480.5
455.6
437.5
418.0
F igu r e 4. TGA thermograms of carbosilane polymers 5a -5e
heated to 1000 °C under a nitrogen atmosphere at 20 °C/min.
proportional to the molar content of the DSCB monomer
3a in the polymer (see inset, Figure 3). The resultant
cross-linked materials are insoluble in both polar and
nonpolar solvents, while a similarly heat-treated poly-
mer containing no DSCB rings (polymer 5e) undergoes
no changes in NMR spectra and remains soluble in
solvents such as THF, hexane, or chloroform. Thus,
these experiments indicated that the cross-linking reac-
tion resulted from the opening of the DSCB ring.
F igu r e 3. Representative DSC scan (polymer 5a ) and (inset)
a plot of the enthalpy of the reaction vs comonomer content.
All DSC data were recorded using a heating rate of 10 °C/
min.
Thermal gravimetric analysis (TGA) was used to
determine the thermal stability and the char yield for
both the original polymers and the hydrogenated poly-
mers. As mentioned before, the thermal stabilities of
the original olefin-containing polymers were relatively
low.31 Both the unsaturated homopolymers and copoly-
mers started to lose weight (5%) between 150 and 300
°C. In contrast, thermogravimetric analysis results for
the saturated polymer 5a (Figure 4) showed that no
weight loss occurs before 470 °C on heating in an inert
atmosphere, even in the region where cross-linking
occurred, as was observed by DSC. For the polymer 5b,
an even higher onset temperature for weight loss of 480
°C was observed. In both cases, a significant char yield
of solid residue (presumably SiCx) is obtained on py-
rolysis (25% for polymer 5a and 55% for polymer 5b by
1000 °C). Thus, the result of this thermosetting ROP
process is a three-dimensional cured network that
resists thermal decomposition to high temperatures and
yields a substantial solid residue even after heating to
1000 °C. Since cross-linking generally enhances thermal
stability, this should also be reflected in the decomposi-
tion temperatures of the copolymers, the temperature
at which 5% weight loss occurs, as determined by TGA.
As shown in Figure 4, the TGA results clearly demon-
strated the difference in thermal stability among these
materials. In the comparison of thermal stability among
polymers 5a and 5c-5e, the thermal stability and char
yield increase with an increase in the concentration of
DSCB rings in the main chain.
by the complete disappearance of the olefin peaks in the
1H NMR spectra (Figure 1). After reduction, GPC
analyses showed that the molecular weights of the
polymers had increased very slightly, which indicated
there was no chain degradation during this process
(Table 1).
Th er m a l P r op er ties. The thermal behavior of the
hydrogenated polymers was examined by DSC. In the
thermogram of homopolymer 5a (Figure 3), a glass
transition was observed at around -65 °C, along with
a large exotherm, which starts at about 210 °C and
concludes at approximately 300 °C (with a maximum
at 250 °C). In the thermogram of polymer 5b, in which
phenyl replaces methyl as the other DSCB substituent,
a glass transition temperature was observed at -5 °C
along with a somewhat sharper strong exotherm be-
tween 220 and 290 °C. Interestingly, the starting
temperature for this ring-opening reaction is signifi-
cantly higher than that which has been reported for
other small disilacyclobutane compounds like 1,1,3,3-
tetramethyl-1,3-disilacyclobutane (170 °C) or 1,1,3,3-
tetraphenyl-1,3-disilacyclobutane (180 °C).30
For all of the other hydrogenated polymers (5c-e), a
glass transition was also observed between -60 and -70
°C (see Table 1), and this transition temperature was
nearly invariant with copolymer stoichiometry. The Tg
was reversible during the second scan, provided that
temperatures did not exceed 150 °C for an extended
period of time. At higher temperatures, for copolymers
5c and 5d , an irreversible exothermic transition was
also observed in the range 200-300 °C, which presum-
ably corresponds to the opening of the DSCB rings. The
starting temperature for this reaction is, again, higher
than that which has been reported for other small DSCB
compounds. This ca. 40 °C difference in the starting
temperature of this curing exotherm from that of the
small DSCB may relate to the relatively lower mobility
of the reactive DSCB groups in the polymer chain and
the need to move them into the proper relative position
to undergo the cross-linking reaction. The enthalpy (∆H)
for this ring-opening reaction, obtained from the inte-
grated area under the exothermic peak, is directly
Cu r in g Stu d ies. The thermally induced ring-opening
polymerization of the DSCB rings in these polymers
resulted in distinct changes in the infrared spectrum.
Mixtures of the un-cross-linked and cross-linked forms
of polymer 5a were prepared in Nujol and were used
for IR analysis. The IR spectra showed that the intensity
of the sharp peak at 930 cm-1, which was assigned to
the wagging mode of the CH2 on the DSCB rings,
decreased gradually as the curing reaction proceeded
and that a broad peak is formed at 1050 cm-1, which is
assigned to the stretching mode for the bridging CH2
group in the SiCH2Si open-chain structure (Figure
5).27,32,33

Macromolecules, Vol. 37, No. 14, 2004
Cross-Linkable Carbosilane Polymers 5261
Ta ble 2. Su r fa ce Ar ea Ch a n ges of Cu r ed Sp ecim en s in
Differ en t Solven ts a fter Sw ellin g for 48 h (Mea su r ed a t
25 °C, a fter Cu r in g for 8 h a t 280 °C u n d er Nitr ogen )
area changes (%) in
ethyl
medium cured polymers hexane chloroform acetone alcohol
5a
5c
5d
0
24
150
0
6
110
0
0
14
0
0
9
for 2 h. The films were then removed from the glass vial
and cut into thin strips. The strips were then heated to
a temperature of 280 °C for 8 h in nitrogen to complete
the curing process. The cured polymers (5a , 5c, 5d ) were
insoluble in all of the common solvents, except the
homopolymer 5e which, lacking the imbedded carbosi-
lane rings, could not be cured under the same condi-
tions. The completely cured polymer samples were
placed in different solvents at room temperature to test
their solubility and swelling characteristics. Cured
homopolymer 5a shows no observable swelling over 48
h in all the solvents, while the copolymers 5c and 5d
all swell to a certain degree. The surface area of the
cured copolymer strips increases with the swelling time
up to 48 h, while no change was detected in the
thickness of these samples. For the cured polymer 5d ,
after swelling for 48 h, the area of the polymer strips
increases by 9-150%, as shown in Table 2. These results
also show that the lower the content of the DSCB moiety
in its backbone, the more the polymer swells after cross-
linking. The results also show that the polymers swell
more in nonpolar solvents than in polar solvents.
Before curing, the polymers are transparent, very
viscous materials. Cured films of the polymers 5a and
5c were hard and brittle, while a cured film of the 10:1
copolymer 5d was a transparent, flexible, material with
rubberlike properties. Samples obtained by curing the
polymer 5a in glass tubes, sealed at one end and heated
to 280 °C for 8 h, were easily removed from the tubes
on cooling, owing to shrinkage occurring after cross-
linking. The density was changed from 0.92 to 0.94
g/cm3, corresponding to a reduction in volume of 2.1%.
A detailed study of the mechanical properties of these
materials is currently in progress.
F igu r e 5. IR spectra of polymer 5a in Nujol: (A) uncured,
(B) cured at 220 °C for 2 h, (C) cured at 240 °C for 4 h, and
(D) cured at 280 °C for 8 h.
F igu r e 6. 29Si NMR spectra of cured polymer 5a : (A) uncured,
(B) cured at 220 °C for 2 h, (C) cured at 240 °C for 4 h, and
(D) cured at 280 °C for 8 h.
In an effort to better understand the cross-linking
chemistry of the polymers, solid-state NMR spectra were
taken for non-, partially, and fully cross-linked polymer
5a . There were no notable changes in peak positions in
the 13C SS-NMR spectra during the cross-linking pro-
cess. Using 29Si SS-NMR under magic angle spinning
(MAS), it was found that nearly all of the DSCB rings
undergo ring opening after heating to 280 °C for 8 h
under an inert atmosphere (Figure 6). This is monitored
by the loss of a peak at 4.7 ppm (assigned to Si in the
strained DSCB ring) and the growth of a peak at 2.3
ppm (assigned to Si in the linear -SiCH2- unit) in the
29Si NMR spectrum of the polymer.34 Comparison of the
line widths of the two peaks shows the silicon atoms in
the cross-linked polymer are more restricted to motion
than in the original polymer, as would be expected for
a cross-linked polymer. These IR and NMR studies show
clearly that the cross-linking mechanism involves the
ring opening of the DSCB rings in the polymers and that
this process occurs without side reactions to yield the
corresponding three-dimensional, cured, carbosilane
network structures.
Exp er im en ta l Section
Mater ials. All manipulations involving air- and/or moisture-
sensitive materials were performed under a nitrogen atmo-
sphere with glovebox and conventional Schlenk line tech-
niques. All ether and hydrocarbon solvents were distilled
before use from their purple sodium/benzophenone solutions.
All the chemicals were purchased from Aldrich Chemical Co.
4-Bromo-1-butene (97%), magnesium (99%), methylmagnesium
bromide (3.0 M solution in diethyl ether), 1,2-bis(chlorodi-
methylsilyl)ethane (96%), tripropylamine (99%), p-toluene-
sulfonylhydrazide (97%), and the Grubbs second-generation
catalyst were all used as received without further purification.
Chloromethyldichloromethylsilane, chloromethyldichlorophe-
nylsilane, and 1,3-dichloro-1,3-dimethyl-1,3-disilacyclobutane
were prepared according to the literature methods and purified
by distillation.25,26
In str u m en ta tion . All of the solution NMR spectra were
obtained on Varian Unity-300 or Unity-500 MHz spectrom-
eters. 1H and 13C spectra were referenced to the solvent peaks,
and 29Si spectra were referenced to TMS. Infrared spectra were
taken with a Perkin-Elmer Paragon 1000 spectrometer. The
molecular weight of the polymers was measured on a Waters
GPC system equipped with a refractive index detector and
three Styragel columns packed with 5 µm particles (HR1:
effective molecular weight 100-5000; HR3: effective molecular
weight 500-30 000; HR4: effective molecular weight 5000-
A swelling test was carried out for some of the cross-
linked polymers according to the method described in
ref 35. Thin films of the cyclolinear carbosilane polymer
5a and the copolymers 5c and 5d were partially cured
in a glass vial in nitrogen at a temperature of 200 °C

5262 Wu et al.
Macromolecules, Vol. 37, No. 14, 2004
500 000) using THF as eluent at a flow rate of 1.0 mL/min.
Molecular weights were reported relative to polystyrene
standards. DSC measurements were obtained on a TA 2920
instrument. The transition temperatures were determined by
using a heating rate of 10 °C/min after an initial heating/
cooling cycle to 100 °C. TGA studies were carried out using a
Mettler-Toledo thermogravimetric analyzer at a rate of 20 °C/
min under a flowing nitrogen atmosphere. All of the solid-state
NMR spectra were acquired on a Chemagnetics Infinity 360
MHz spectrometer. 29Si spectra were externally referenced to
TMS using tetrakis(trimethylsilyl)silane and acquired under
single-pulse conditions with decoupling during acquisition and
magic angle spinning (MAS); the 29Si pulse width was 4.5 µs
portions during the course of 1 h, while cooling occasionally
with a cold water bath to maintain the reaction temperature
between 40 and 50 °C. After refluxing for another several
hours, the reaction mixture was cooled to room temperature.
50 mL of dry hexane was added to precipitate the magnesium
salt from the THF solution. All of the combined liquid (THF/
hexane/product) was transferred to another flask via a can-
nula. After removal of the solvents under atmospheric pressure
with a N2 stream, the residue was collected and purified by
fractional distillation one or two times using a packed column.
The final yield was 6.6 g (49%).
Procedure b: 2.34 g (12.6 mmol) of 1,3-dichloro-1,3-dimethyl-
1,3-disilacyclobutane mixed with 50 mL of THF was charged
in a three-necked 250 mL flask equipped with a reflux
condenser. Butenylmagnesium bromide (37.5 mmol; as pre-
pared in part 3) was added via a syringe over 1 h. The reaction
mixture was continuously stirred with a magnetic stir bar.
Some magnesium salts formed during addition of the 3-bute-
nylmagnesium bromide. The resulting mixture was further
refluxed for 2 days, and then the solution was cooled to room
temperature. The excess Grignard reagent was destroyed by
adding 40 mL of saturated aqueous ammonium chloride
solution. The solution formed two phases with the excess
magnesium dissolving in the acidic aqueous layer. The organic
phase was separated and dried overnight by using anhydrous
sodium sulfate. The solvent was removed by atmospheric
distillation, and a final distillation under reduced pressure
using a packed column gave 2.31 g (10.3 mmol) of pure product
(mixture of trans and cis isomers). The final yield of 3a was
for a π/2 pulse, and the optimal relaxation delay was 60 s. 13
C
spectra were externally referenced to TMS using hexameth-
ylbenzene and acquired under the same conditions as the 29Si
spectra.
1. P r ep a r a tion of Bu ten ylch lor om eth ylm eth ylch lo-
r osila n e (2a ). Compound 2a was prepared by a two-step
reaction process. The first step of the preparation of the
Grignard reagent between 4-bromo-1-butene and magnesium
turnings was carried out in a 250 mL three-necked, round-
bottomed flask with stirring bar, addition funnel, and reflux
condenser. The flask was charged with 6.0 g (0.25 mol) of
magnesium turnings in 10 mL of dried THF. 4-Bromo-1-butene
(27.0 g, 0.2 mol) dissolved in 50 mL of dry THF was added
slowly within 1 h by means of an addition funnel. A heating
gun was used to warm the flask to initiate the reaction. After
the reaction mixture was stirred at 45 °C for 2 h, the reaction
was stopped, and the remaining magnesium was removed and
weighed to determine the conversion (97%).
A 1 L three-necked, round-bottomed flask was charged with
24.5 g (0.15 mol) of chloromethyldichloromethylsilane and 150
mL of THF. Freshly made butenylmagnesium bromide (0.15
mol) was added under vigorous stirring within 1 h. The
exothermic reaction that occurred resulted in the formation
of solid magnesium bromide as a byproduct. The reaction was
stirred at 60 °C for 8 h. After the reaction mixture was cooled
to room temperature, 200 mL of dried hexane was added to
precipitate the magnesium salt. Then the liquid was trans-
ferred to another 1 L flask by using a Teflon cannula. Two
100 mL portions of THF were used to extract the product from
the salts. All of the collected liquid was combined for distil-
lation. The solvents were stripped off by atmospheric pressure
distillation. Vacuum distillation of the residue gave 21.2 g (0.13
mol) of product collected at 40-44°C/0.5 mmHg. Yield: 77.3%.
1H NMR (CDCl3): δ 0.24 (s, 3H, SiCH3), 0.85 (t, J ) 7.2 Hz,
2H, SiCH2CH2CH), 2.12 (m, 2H, SiCH2CH2CH), 3.70 (s, 2H,
CH2Cl), 5.03 (d, 2H, CH2CHCH2), 5.81 (m, 1H, CH2CHCH2).
13C NMR (CDCl3): δ -4.95 (SiCH3), 12.68 (SiCH2CH2), 28.75
(SiCH2CH2CH), 37.25 (SiCH2Cl), 116.80 (CH2CHCH2), 140.72
(CH2CHCH2). 29Si NMR (CDCl3): δ 23.41.
2. P r ep a r a tion of Bu ten ylch lor om eth ylp h en ylch lo-
r osila n e (2b). 2b was prepared in an analogous manner to
the synthesis of 2a described in the preceding section by using
chloromethylphenyldichlorosilane as starting material. The
boiling point and final yield of 2b were 100°C/0.5 mmHg and
76.3%. 1H NMR (CDCl3): δ 1.40 (t, J ) 7.4 Hz, 2H, SiCH2-
CH2), 2.28 (m, 2H, SiCH2CH2), 3.20 (s, 2H, CH2Cl), 5.05 (d,
2H, CH2CHCH2), 5.9 (m, 1H, CH2CHCH2), 7.40-7.74 (m, 5H,
C6H5). 13C NMR (CDCl3): δ 13.46 (SiCH2CH2), 26.72 (SiCH2CH2-
CH), 28.99 (SiCH2Cl), 114.33 (CH2CHCH2), 128.45, 131.32,
133.85, 134.16 (SiC6H5), 139.74 (CH2CHCH2). 29Si NMR
(CDCl3): δ 11.97.
3. P r ep a r a tion of 1,3-Dibu ten yl-1,3-d im eth yl-1,3-d isi-
la cyclobu ten e (3a ). Monomer 3a was prepared by two
procedures. Procedure a: Following the “reverse addition”
procedure described by Kriner, a 500 mL three-necked, round-
bottomed flask was equipped with stirring bar, addition funnel,
and reflux condenser. Then 22.0 g (0.12 mol) of butenylchlo-
romethylmethylchlorosilane in 50 mL of dry THF was added
to bring the silane concentration to about 30%. 0.5 g of
magnesium powder was added to the solution, and the
coupling reaction was initiated by using a heating gun.
Subsequently, 4.8 g (0.2 mol) of magnesium was added in
1
81.7%. H NMR (CDCl3): δ -0.10-0.11 (quintet, 4H, SiCH2-
Si), 0.24 (s, 6H, SiCH3), 0.78 (t, 4H, SiCH2CH2), 2.16 (m, 4H,
SiCH2CH2), 4.91-5.07 (m, 4H, CH2CHCH2), 5.91 (m, 2H,
CH2CHCH2). 13C NMR (CDCl3): δ 0.71, 0.86 (SiCH3), 0.89, 0.95
(SiCH2Si), 17.67, 17.77 (SiCH2CH2), 27.99, 28.04 (SiCH2CH2),
113.18, 113.20 (CH2CHCH2), 141.53, 141.57 (CH2CHCH2). 29Si
NMR (CDCl3): δ 4.97, 5.04. IR (neat, cm-1): 3076, 2954, 2908,
1639, 1428, 1408, 1340, 1248, 991, 936, 906, 824, 779, 693.
4. P r ep a r a tion of 1,3-Dibu ten yl-1,3-d ip h en yl-1,3-d isi-
la cyclobu ten e (3b). 3b was prepared in an analogous manner
to the synthesis of 3a described in the preceding section from
butenylchloromethylphenylchlorosilane. Purification by col-
umn chromatography gave the product as a mixture of trans
and cis isomers. Yield: 51.2%. 1H NMR (CDCl3) (both trans
and cis isomers): δ 0.56-0.66 (m, 4H, SiCH2Si), 1.01-1.22 (m,
4H, SiCH2CH2), 2.10-2.26 (m, 4H, SiCH2CH2), 5.01-5.15 (m,
4H, CH2CHCH2), 5.80-6.05 (m, 2H, CH2CHCH2), 7.37-7.74
(m, 10H, C6H5). 13C NMR (CDCl3): δ -0.83, -0.75 (SiCH2Si),
16.81, 16.87 (SiCH2CH2), 27.80, 27.98 (SiCH2CH2), 113.28,
113.45 (CH2CHCH2), 127.95, 127.97, 129.31, 129.43, 133.84,
138.47, 138.77 (SiC6H5), 141.09, 141.17 (CH2CHCH2). 29Si
NMR (CDCl3): δ 0.82, 1.01. IR (neat, cm-1): 3066, 2973, 2910,
1638, 1426, 1347, 1111, 992, 936, 908, 759, 732, 698, 626.
5. P r ep a r a tion of 1,2-Bis(bu ten yld im eth ylsilyl)eth a n e
(3c). 30 g (0.14 mol) of 1,2-bis(chlorodimethylsilyl)ethane was
mixed with 150 mL of THF in a two-necked 500 mL flask
equipped with a reflux condenser. 0.30 mol of 3-butenylmag-
nesium bromide (as prepared in section 3) was added slowly
via a syringe over 2 h. Some magnesium salts formed during
addition of the butenylmagnesium bromide. The resulting
mixture was further refluxed for 1 day, and then the solution
was cooled to room temperature. 100 mL of hydrochloric acid
(1 M) solution was added very slowly to destroy any excess
Grignard reagents and dissolve the magnesium salts. The
solution formed two layers. The organic phase was separated
and dried by anhydrous sodium sulfate for several hours. The
solvent was removed by atmospheric distillation, and the final
1
yield of 3c was 83.2%; bp 67°C/0.9 mmHg. H NMR (CDCl3):
δ -0.02 (s, 12H, SiCH3), 0.40 (s, 4H, SiCH2CH2Si), 0.62 (t, 4H,
SiCH2CH2CH), 2.04 (m, 4H, SiCH2CH2CH), 4.87-5.04 (m, 4H,
CH2CHCH2), 5.88 (m, 2H, CH2CHCH2). 13C NMR (CDCl3): δ
-3.68 (SiCH3), 7.39 (SiCH2CH2Si), 14.06 (SiCH2CH2CH), 28.28
(SiCH2CH2CH), 112.83 (CH2CHCH2), 142.08 (CH2CHCH2). 29Si
NMR (CDCl3): δ 4.34. IR (neat, cm-1): 3076, 2952, 2904, 1640,
1411, 1247, 1133, 1055, 992, 905, 829, 778.

Macromolecules, Vol. 37, No. 14, 2004
Cross-Linkable Carbosilane Polymers 5263
Gen er a l P olym er iza tion P r oced u r es. In
a
glovebox
The temperature was increased to 110 °C for another 4 h. After
removing the solid precipitate, the entire liquid mixture was
added to methanol, and the product was recovered by decanta-
tion and dried in a vacuum. Yields typically ranged from 80
to 90% with the lost yield attributed to polymer not recovered
from the precipitation. Polymers 5a -e were synthesized by
this method and characterized by standard methods including
1H NMR, 13C NMR, 29Si NMR, IR, and GPC.
under an inert N2 atmosphere, the dry monomer or mixture
of monomers and the second-generation Grubbs catalyst (1 wt
%) were added to a round-bottom flask. The mixture was
stirred at room temperature in the glovebox until a clear
solution resulted, which indicated that the catalyst was
completely dissolved in the monomer. The flask was then
removed from the glovebox, and the contents were stirred
under vacuum on a Schlenk line and heated in an oil bath to
40 °C. After 1 day the reaction mixture was again taken into
the glovebox, and an additional aliquot of catalyst was added.
The mixture was then stirred at 65 °C until the evolution of
ethylene was no longer visible and the stir bar did not stir.
The reaction was terminated by exposure to air. The resultant
polymer was dissolved in toluene or THF, treated with
activated carbon, passed through silica gel column, twice
precipitated by pouring into methanol, and then vacuum-dried.
Yields for these polymerization reactions were all above 85%
with some loss in yield attributed to polymer lost in the
workup. The polymers obtained as colorless or light yellow,
very viscous materials. Polymers 4a -e were synthesized by
this method and characterized by standard methods including
1H, 13C, and 29Si NMR, IR, and GPC.
1
P olym er 5a . H NMR (CDCl3): δ -0.03 (m, 4H, SiCH2Si),
0.22 (s, 6H, SiCH3), 0.69 (br, 4H, SiCH2CH2), 1.37 (br, 8H,
SiCH2CH2CH2CH2CH2CH2Si). 13C NMR (CDCl3): δ 0.79, 0.83
(SiCH3), 0.91 (SiCH2Si), 18.69, 18.74 (SiCH2CH2CH2), 23.85,
23.87 (SiCH2CH2CH2), 33.26 (SiCH2CH2CH2). 29Si NMR
(CDCl3): δ 4.33, 4.38. IR (neat, cm-1): 2952, 2918, 2851, 1459,
1406, 1340, 1247, 930, 894, 858, 823, 778.
P olym er 5b. 1H NMR (CDCl3): δ 0.57 (br, 4H, SiCH2Si),
1.01 (br, 4H, SiCH2CH2), 1.35 (br, 8H, SiCH2CH2CH2), 7.37-
7.67 (br, 10H, SiC6H5). 13C NMR (CDCl3): δ -1.08 (SiCH2Si),
17.67 (SiCH2CH2CH2), 23.83 (SiCH2CH2CH2), 33.05 (SiCH2-
CH2CH2), 127.89, 129.23, 133.79, 139.74 (SiC6H5). 29Si NMR
(CDCl3): δ -0.01, 0.21. IR (neat, cm-1): 3065, 2919, 2851,
1648, 1484, 1458, 1426, 1348, 1186, 1110, 997, 934, 909, 763,
732, 699, 610.
P olym er 4a . 1H NMR (CDCl3): δ -0.01-0.08 (m, 4H,
SiCH2Si), 0.23 (s, 6H, SiCH3), 0.77 (br, 4H, SiCH2CH2), 2.08
(br, 4H, SiCH2CH2), 5.49 (br, 2H, CH2CHCHCH2). 13C NMR
(CDCl3): δ 0.83 (SiCH3), 0.99 (SiCH2Si), 18.54, 18.62 (SiCH2-
CH2), 26.75 (SiCH2CH2), 131.46 (CH2CHCHCH2, cis-olefin),
P olym er 5c. 1H NMR (CDCl3): δ -0.04 (16H, SiCH2Si and
SiCH3, overlapped), 0.22 (6H, SiCH3), 0.38 (4H, SiCH2CH2Si),
0.51 (4H, SiCH2CH2), 0.69 (4H, SiCH2CH2), 1.32-1.37 (16H,
SiCH2CH2CH2CH2CH2CH2Si). 13C NMR (CDCl3): δ -3.58
(SiCH3), 0.84 (SiCH3), 0.93 (SiCH2Si), 7.49 (SiCH2CH2Si), 15.02
(SiCH2CH2, 18.72, 18.78 (SiCH2CH2), 23.89, 24.12 (SiCH2CH2),
33.28, 33.70 (SiCH2CH2CH2). 29Si NMR (CDCl3): δ 3.89
(SiCH2CH2Si), 4.33, 4.37 (SiCH2Si). IR (neat, cm-1): 2952,
2919, 2872, 1460, 1407, 1340, 1246, 1186, 1132, 1053, 934, 908,
827, 779, 736, 689, 663.
131.65 (CH2CHCHCH2, trans-olefin). 29Si NMR (CDCl3):
δ
4.78, 4.85. IR (neat, cm-1): 3008, 2952, 2912, 2850, 1655, 1612,
1442, 1405, 1342, 1247, 1152, 965, 931, 822, 688.
P olym er 4b. 1H NMR (CDCl3): δ 0.47-0.49 (br, 4H, SiCH2-
Si), 0.81-0.95 (br, 4H, SiCH2CH2), 1.86-2.06 (br, 4H,
SiCH2CH2CH), 5.19-5.42 (br, 2H, CH2CHCH2), 7.19-7.56 (br,
5H, SiC6H5). 13C NMR (CDCl3): δ -0.93 (SiCH2Si), 17.46
(SiCH2CH2CH), 26.47 (SiCH2CH2CH), 131.36 (CH2CHCHCH2),
127.90, 128.03, 129.25, 133.83, 135.22 (SiC6H5). 29Si NMR
(CDCl3): δ 0.40, 0.56. IR (neat, cm-1): 3066, 3007, 2911, 2840,
1647, 1588, 1427, 1347, 1301, 1260, 1111, 966, 935, 761, 732,
699, 608.
P olym er 5d . 1H NMR (CDCl3): δ -0.05-0.05 (SiCH2Si and
SiCH3, overlapped), 0.22 (SiCH3), 0.38 (SiCH2CH2Si), 0.50-
0.53 (SiCH2CH2), 0.69 (SiCH2CH2), 1.32 (SiCH2CH2CH2CH2-
CH2CH2Si). 13C NMR (CDCl3): δ -3.59 (SiCH3), 0.83 (SiCH3),
0.92 (SiCH2Si), 7.51 (SiCH2CH2Si), 15.04 (SiCH2CH2, 18.79
(SiCH2CH2), 23.85, 24.13 (SiCH2CH2), 33.70 (SiCH2CH2CH2).
29Si NMR (CDCl3): δ 3.87. IR (neat, cm-1): 2950, 2918, 2851,
1460, 1407, 1186, 1131, 1053, 933, 830, 778, 712, 690.
P olym er 5e. 1H NMR (CDCl3): δ -0.04 (12H, SiCH3), 0.38
(4H, SiCH2CH2Si), 0.50 (4H, SiCH2CH2CH2), 1.31 (8H,
SiCH2CH2CH2). 13C NMR (CDCl3): δ -3.617 (SiCH3), 7.50
(SiCH2CH2Si), 15.02 (SiCH2CH2CH2), 24.12 (SiCH2CH2CH2),
33.69 (SiCH2CH2CH2). 29Si NMR (CDCl3): δ 3.87. IR (neat,
cm-1): 2951, 2919, 2791, 1459, 1408, 1246, 1187, 1132, 1053,
831, 714.
P olym er 4c. 1H NMR (CDCl3): δ -0.015 (SiCH2Si and
SiCH3, overlapped), 0.24 (SiCH3), 0.42 (SiCH2CH2Si), 0.58-
0.64 (SiCH2CH2), 0.77 (SiCH2CH2), 1.99-2.03 (SiCH2CH2CH),
5.33-5.47 (CH2CHCHCH2). 13C NMR (CDCl3): δ -3.51 (SiCH3),
0.85 (SiCH3), 1.01 (SiCH2Si), 7.49 (SiCH2CH2Si), 14.94, 15.44
(SiCH2CH2CH), 18.55, 18.63 (SiCH2CH2CH), 21.62, 27.04
(SiCH2CH2CH), 131.61-131.83 (multiple signals, CHdCH).
29Si NMR (CDCl3): δ 4.20, 4.78, 4.85. IR (neat, cm-1): 2951,
2902, 1696, 1441, 1407, 1246, 1131, 1053, 935, 903, 829, 779,
713, 688.
Sw ellin g. Based on a previously described procedure,35
swelling studies for the cured polymers were carried out in
the following manner: ca. 0.5 g samples of the polymers were
partially cured in a glass vial under nitrogen at a temperature
of 200 °C for 2 h. The partially cured polymers were then
removed from the glass vial as intact films and cut into strips
with dimensions of ca. 0.1 × 5 × 10 mm3. The resultant
polymer samples were then heated to a temperature of 280
°C under nitrogen for 8 h to complete the cure process. After
curing, the samples were immersed in the indicated solvents,
and the change in the area of the films was measured.
P olym er 4d . 1H NMR (CDCl3): δ -0.015 (SiCH2Si and
SiCH3, overlapped), 0.24 (SiCH3), 0.42 (SiCH2CH2Si), 0.58-
0.64 (SiCH2CH2), 1.99-2.03 (SiCH2CH2CH), 5.33-5.47 (CH2CH-
CHCH2). 13C NMR (CDCl3): δ -3.51 (SiCH3), 1.01 (SiCH2Si),
7.49 (SiCH2CH2Si), 14.94, 15.44 (SiCH2CH2CH), 21.62, 27.04
(SiCH2CH2CH), 131.61-131.83 (multiple signals, CHdCH).
29Si NMR (CDCl3): δ 4.20. IR (neat, cm-1): 2951, 2902, 1696,
1441, 1407, 1246, 1131, 1053, 935, 903, 829, 779, 713, 688.
P olym er 4e. 1H NMR (CDCl3): δ -0.04 (12H, SiCH3), 0.38
(4H, SiCH2CH2Si), 0.59 (4H, SiCH2CH2CH), 2.01 (4H, SiCH2-
CH2CH), 5.35, 5.44 (2H, SiCH2CH2CH). 13C NMR (CDCl3): δ
-3.56 (SiCH3), 7.48 (SiCH2CH2Si), 14.94 (SiCH2CH2CH), 27.02
(SiCH2CH2CH), 131.85 (CH2CH2CH). 29Si NMR (CDCl3): δ
4.19. IR (neat, cm-1): 2952, 2903, 1725, 1407, 1249, 1175, 1132,
1054, 967, 836, 719, 689.
Gen er a l Hyd r ogen a tion P r oced u r e for th e P olym er s.
For preparation of the corresponding saturated hydrocarbon
polymers, in a typical experiment, 0.2 g (1 mmol) of the
ADMET polymer 4a mixed with 20 mL of xylene was added
to a two-necked round-bottom flask with a reflux condenser.
0.29 g (2 mmol) of tripropylamine (TPA) and 0.37 g (2 mmol)
of p-toluenesulfonhydrazide (TSH) were added to this flask,
and the mixture was heated at 100 °C in an oil bath for 4 h
under nitrogen. After cooling to room temperature, an ad-
ditional equivalent of TPA and TSH was added to the mixture.
Con clu sion s
A series of novel cyclolinear polymers with 1,3-
disilacyclobutane (DSCB) rings imbedded into the main-
chain structure were obtained by using ADMET polym-
erization. These olefin-containing, cyclolinear, carbosilane
polymers were then hydrogenated with p-toluenesulfon-
hydrazide to produce a saturated hydrocarbon structure
in the main chain without affecting the imbedded DSCB
rings. NMR spectroscopy and GPC analyses showed that
all of the resultant, relatively high molecular weight
polymers have well-defined, regular structures consist-
ing of DSCB rings [-SiMe(CH2)2SiMe-] linked by linear
hydrocarbon or carbosilane chains. DSC studies of these

5264 Wu et al.
Macromolecules, Vol. 37, No. 14, 2004
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tures (-70 f -60 °C for the methyl-substituted poly-
mers and -5 °C for the phenyl-substituted polymer)
followed, on first heating, by a strong exotherm centered
at ca. 250 °C. IR and solid-state NMR spectra, along
with the change in physical form, showed that the
second transition at 250 °C corresponds to the thermally
induced ring opening of the DSCB rings, resulting in a
transparent, cross-linked, solid material having the
shape of the container with little overall shrinkage. TGA
of the reduced form of the homopolymer under N2
showed no weight loss until 470-480 °C with char yields
of 25% (polymer 5a ) and 55% (polymer 5b) after
pyrolysis to 1000 °C.
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Ack n ow led gm en t . Financial support from the
Chemistry Division of the National Science Foundation
through Grant CHE-0109643 is gratefully acknowl-
edged. The authors also acknowledge the 2001 Mettler-
Toledo Thermal Analysis Educational Grant in honor
of Professor Edith Turi, which made possible the
purchase of the TGA instrument that was used in this
work.
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(34) The assignment of the solid-state NMRspectra was aided by
the examination of the solution NMR spectra of the polymer
prepared by ring-opening polymerization of the model com-
pound 1,3-dihexyl-1,3-dimethyl-1,3-disilacyclobutane. Mono-
mer: 13C NMR (CDCl3): δ (ppm) 0.89 (SiCH3), 0.95 (SiCH2Si),
14.49 (CH3CH2-), 18.80 (SiCH2CH2-), 22.95 (CH3CH2-),
24.08 (SiCH2CH2-), 32.32 (CH3CH2CH2-), 33.41 (SiCH2-
CHCH2-). 29Si NMR (CDCl3): δ (ppm) 4.50. Polymer: 13C
NMR (CDCl3): δ (ppm) 1.26 (SiCH3), 3.91 (SiCH2Si), 14.45
(CH3CH2-), 19.32 (SiCH2CH2-), 23.05 (CH3CH2-), 24.48
(SiCH2CH2-), 32.02 (CH3CH2CH2-), 33.91 (SiCH2-
CHCH2-). 29Si NMR (CDCl3): δ (ppm) 2.10.
(35) Marks, M. J .; Sekinger, J . K. Macromolecules 1994, 27, 4106.
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