Transparent room temperature cured elastomers based on bisphenol A

Article abstract of DOI:10.1002/pola.27027

The synthesis of a divinyl-terminated resin from commercially available bisphenol A and polymerization with silane containing compounds utilizing a room temperature hydrosilylation reaction is demonstrated. The transparent, clear polymers exhibit excellent thermal and oxidative stability while maintaining elastomeric properties and good hardness. These polymers also have the ability to be dyed any color in the spectrum.

Full text of DOI:10.1002/pola.27027

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
Transparent Room Temperature Cured Elastomers Based
on Bisphenol A
Mollie B. Schear, Matthew Laskoski
Chemistry Division, Code 6127, Naval Research Laboratory, Washington, District of Columbia
20375-5320
Correspondence to: M. Laskoski (E-mail: matthew.laskoski@nrl.navy.mil)
Received 18 October 2013; accepted 8 November 2013; published online 1 December 2013
DOI: 10.1002/pola.27027
ABSTRACT: The synthesis of a divinyl-terminated resin from
polymers also have the ability to be dyed any color in the
spectrum. Published 2013.† J. Polym. Sci., Part A: Polym.
Chem. 2014, 52, 523–526
commercially available bisphenol A and polymerization with
silane containing compounds utilizing
a room temperature
hydrosilylation reaction is demonstrated. The transparent, clear
polymers exhibit excellent thermal and oxidative stability while
maintaining elastomeric properties and good hardness. These
KEYWORDS: Crosslinking; thermal properties; thermosets
Depending on the number of SiAH groups in the curing additive,
a linear to highly crosslinked polymer can be formed.
INTRODUCTION Silicone containing polymers exhibit supe-
rior flame resistant properties when compared with their
hydrocarbon counterparts while still retaining good elasto-
meric properties over a wide temperature range. Quantum
leaps in new technology have outpaced the current materials
available in a wide range of applications especially in the
modern aerospace, marine, energy, and electrical industries.1
Two vital requirements of a good elastomeric material for
these applications in extreme environments are excellent
toughness and wear as well as good thermal properties up
to several hundred degrees. Siloxane polymers have shown
some promise as coatings, paints and adhesives because of
their flexibility, toughness, and heat-resistant properties but
they typically exhibit quite low glass transition temperatures
A liquid divinyl terminated resin system with the ability to con-
trol the crosslinking density while still being easily processed
into transparent shaped composites or thin elastomeric films
using a cost effective technique such as resin transfer molding
or by spray coating at ambient temperatures would be benefi-
cial. Another added benefit of the polymer’s transparent nature
is the ability to dye to any color in the spectrum.
In this article, we will discuss the synthesis, polymerization,
and physical properties of a liquid divinylsilane-terminated
aromatic resin system based on bisphenol A and show the
conversion of this resin to a transparent polymer via a room
temperature hydrosilylation reaction.
1
ꢀ
(Tg) and are not suited for long term use over 200 C.
EXPERIMENTAL
Efforts have been focused on increasing the toughness and the
thermal stability at higher temperatures of elastomeric materi-
als. This can be achieved by the incorporation of aromatic units2
within the polymer backbone but can significantly add to the
cost of the resin limiting it to specialty applications.3 To circum-
vent this drawback, modification of the reaction chemistry to
produce a liquid divinylsilane terminated resin from a bisphenol
using commodity chemicals (e.g., bisphenol A) has been demon-
strated.2 These divinyl terminated monomers are then converted
to a linear or crosslinked polymer using hydrosilylation chemis-
try, Scheme 1, in the presence of a transition metal catalyst4 and
a multiple SiAH containing compound.5–9 In this reaction, the Pt
catalyst facilitates the addition of the SiAH to the vinyl group.
All starting materials were of reagent grade and used with-
out further purification. The divinyl-terminated bisphenol A
based resin was prepared using a modified procedure from
Bublewitz et al.3 Differential scanning calorimetric (DSC)
analysis was performed on a TA Instruments DSC 2920
modulated thermal analyzer at a heating rate of 10 C min
and a nitrogen purge of 100 cm3 min21. The glass Tg was
reported as the temperature centered at the midpoint
between the linear baselines of a DSC scan. Thermogravimet-
ric analysis (TGA) was performed on a TA Instruments TGA
Q600 at a heating rate of 10 ꢀC min21 under a nitrogen or
air purge of 100 cm3 min21. Infrared (IR) spectra were
21
ꢀ
This article was published online on December 1, 2013. An error was subsequently identified. This notice is included in the online
version to indicate that it has been corrected on January 30, 2014.
Published 2013. †This article is a U.S. Government work and is in the public domain in the USA.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 523–526
523

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 1 General reaction of a divinylsilane compound with
a SiAH compound.
recorded as films on NaCl disks using a Nicolet iS50 FTIR
€
spectrometer. NMR was performed on a Bruker ADVANCE
300 spectrometer. The Shore A hardness was measured
using a PTC Instruments Model 306L durometer.
Synthesis of the Divinyl-Terminated Bisphenol A Resin 1
To a flame dried 1000 mL, three necked flask fitted with a
condenser and a nitrogen inlet were added bisphenol A 2
(40.0 g, 175 mmol), triethylamine (122 mL, 88.6 g, 875
mmol) and anhydrous acetone (300 mL). Vinyl(chlorodime-
thyl)silane 3 (57.0 mL, 50.4 g, 419 mmol) was added slowly
via syringe so as to keep the solution under gentle reflux.
During addition of 3 a voluminous white precipitate of
NEt3H1Cl2 was formed. The resulting mixture was stirred
SCHEME 2 Synthesis of divinyl silane resin 1 and polymer 4.
ꢀ
under ambient conditions for 1 h and refluxed at 80 C for 16
RESULTS AND DISCUSSION
ꢀ
h. The product mixture was cooled to 0 C and the precipitate
Divinylsilane-terminated resin 1 was prepared by reacting
bisphenol A 2, chlorodimethylvinylsilane 3 and triethylamine in
dry acetone to afford 1 followed by distillation to afford a pale
yellow oil in 86% yield (Scheme 2). Resin 1 is readily soluble in
most organic solvents due to the presence of aliphatic groups in
the system and exists as a nonviscous liquid at ambient temper-
ature. Conversion of 1 to a linear or networked polymer occurs
at ambient temperature in the presence of any compound con-
taining at least two SiAH moieties and a Pt catalyst using typi-
cal hydrosilylation chemistry.10 In this case, either
tetrakis(dimethylsiloxy)silane (TMSS) or p-dimethylsilylbenzene
(DMSB; Fig. 1) were reacted with 1 in varying ratios in the
presence of a platinum–cyclovinylmethylsiloxane complex in
xylene to facilitate the formation of transparent polymeric mate-
rial 4. The overall molar ratio of silicone vinyl groups to Si-H
groups is 1:1 so that all vinyl groups were reacted.
was filtered under vacuum and washed with cold hexanes.
The solvents were removed by heating at 120 ꢀC for several
hours. The mixture was distilled resulting in a pale yellow oil
1
ꢀ
1 (59.7 g, 86%). B.p: 176 C at 98 mTorr. H-NMR (300 MHz,
CDCl3): d 7.05 (d, 4H, aromatic-H), 6.71 (d, 4H, aromatic-H),
6.23 (dd, 2H, alkene-H), 6.04 (dd, 2H, alkene-H), 5.84 (dd, 2H,
alkene-H), 1.60 (s, 6H, aliphatic-H), and 0.31 (s, 12H, SiACH3).
13C-NMR (300 MHz, CDCl3): d 152.7, 143.8, 137.0, 133.7,
127.6, 119.1 (aromatic, alkene), 41.69, 31.06 (alkane), 21.480
(SiACH3). IR [cm21]: k 3051 (C@CH), 2966 (CH@CH2, CH3),
1606 (C@C), 1508 (C@CH), 1406 (CH@CH2), 1260 (SiACH),
1176 (SiAOACH3), 1011 (aromatic), 920 (SiACH@CH2), 837
(SiAOACH), 788 (aromatic), 708 (CH@CH2).
Polymerization of Divinyl Terminated Resin 1 with
Tetrakis(dimethylsiloxy)silane and p-
Bis(dimethylsilyl)benzene with a Pt Catalyst
A series of samples were prepared with varying ratios of the
silane (SiAH) containing compounds TMSS and DMSB. In a
typical polymerization reaction, a selected amount of the
divinyl terminated resin 1 was placed in a minimal amount of
toluene and the Pt catalyst was added with adequate stirring.
To this solution were added TDMSS and DMSB in varying
A 50:50 TMSS/DMSB mixture was reacted with 1 by the fol-
lowing procedure: To the divinyl terminated resin 1 (0.502
g, 1.26 mmol) in 0.5 mL of anhydrous toluene was added 10
mL of a platinum–cyclovinylmethylsiloxane complex in xylene
with adequate stirring. Tetrakis(dimethylsiloxy)silane (0.12
mL, 0.104 g, 0.316 mmol) and p-bis(dimethylsilyl)benzene
(0.14 mL, 0.123 g, 0.633 mmol) were added simultaneously.
The reaction mixture was stirred vigorously and transferred
to a metal pan treated with a Teflon mold release. The pan
was placed onto a metal block to act as a heat sink to allow
the reaction not to overheat and to minimize bubble forma-
tion. This clear resin can be dyed any color by the incorpora-
tion of the appropriate dye in 1 to 10 wt % into the toluene
solution before the catalyst is added and transferred to the
appropriate mold. After 16ꢀ h at room temperature, the poly-
mer 4 was heated at 100 C for 2 h. Selected samples were
postcured to 300 ꢀC for 1 h before their properties were
determined.
FIGURE 1 Curing additives tetrakis-(dimethylsiloxy)silane (TMSS)
or p-dimethyl-silylbenzene (DMSB).
524
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 523–526

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
mately 212 and 21 ꢀC while 4c displayed Tg’s of approxi-
mately 216 and 17 ꢀC. (Fig. 4) At both extremes, polymers
with 100% of the TMSS curing additive, 4a, exhibited an elas-
tomeric constancy but were brittle when attempting to bend
the samples while the polymeric elastomers 4e prepared from
1 and 100% of DMSB showed a very tacky semi-liquid consis-
tency. The Tg’s for all of the polymeric compositions appeared
between 214 and 16 ꢀC, Table 1, with the magnitude of the
transitions varying based on the ratio of TMSS to DMSB. The
nature of the appearance to two distant Tg’s can be explained
by a phase separation of the aromatic and silicone parts of the
polymer. As more of the DMSB was added (4b–4d) to the
samples they appeared more mechanically robust due to the
incorporation of the aromatic units. DSC analysis of the poly-
mers did not show any visible exothermic transitions indicat-
ing that the polymerization reaction was completeꢀ upon
FIGURE 2 Polymers 4c (left) and 4c dyed orange with 10 wt %
of 9, 10-bis(phenylethynyl)-anthracene (right). [Color figure can
be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
concentrations with good stirring. The solutions were trans-
ferred to a mold and placed on a metal block to act as a heat
sink so the reaction would proceed at a slower rate and mini-
mize bubble formation. After 16 h, the reaction was completed
and the transparent, bubble free polymers were removed from
the mold and the resulting polymer 4 was postcured at 100 ꢀC
for 2 h to finish the cure and remove any reꢀmaining toluene
and selected samples were post-cured at 300 C for 1 h. Addi-
tionally, 4c was dyed by addition of 10 wt % of the orange dye
9, 10-bis(phenylethynyl)anthracene (Fig. 2).
ꢀ
heating to 100 C. Additional postcuring to 200 or 300 C had
no measurable impact on the Tg of the resulting polymer.
Examining the elastic properties of polymer 4, we subjected
the void free flat samples to a Shore A durometer. The results
are reported in Table 1. We see that the hardness decreases
when more of the DMSB is added relative to the TMSS. These
results are expected since the addition of DMSB reduces the
crosslinking density of the resulting polymer and thus making
it more elastic. We were unable to obtain a reliable hardness
measurement for sample 4e due to the tacky consistency of
the polymer. From these Shore A measurements, we can cal-
culate a Young’s modulus for 4a–4d, which vary from around
1–2.7 MPa. These values are similar to those noted for other
polymeric materials such as polypropylene.
Figure 3 shows the 1H-NMR spectra for 4e in CDCl3, which is
the 1:1 molar ratio of 1 to DMSB. What we see in this spectra
is the absence of the vinyl peaks from 1, which appear between
6.2 and 5.8 and the appearance of the ACH2ACH2A peaks
from the hydrosilylated product as a multiplet centered at 0.7
ppm. All other peaks from 4e were present in the spectra.
The thermal and oxidative stability of 4 was assessed by TGA
analyses.11 Figure 5 shows data for 4c as a representative
example of the thermal and oxidative stability. When 1 and
The transparent elastomeric polymer 4b prepared from 1 and
75:25 TMSS/DMSB displayed a two-stage glass Tg of approxi-
FIGURE
wileyonlinelibrary.com.]
3
1H-NMR of linear polymer 4e. [Color figure can be viewed in the online issue, which is available at
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 523–526
525

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 5 TGA thermograms of polymer 4c cured to 100 ꢀC for
FIGURE 4 DSC curves showing the glass Tg of polymers 4b
(Top plot) and (Bottom plot) 4c.
2 h: under N2 (A) and air (B).
CONCLUSIONS
varying ratios of TMSS and DMSB were cured to a maximum
temperature of 100 ꢀC under inert conditions, the resulting
networked polymers 4ꢀa–e showed weight retention of 95%
between 390 and 420 C and overall char yields varied from
58 to 15% for 4a–4e, respectively, upon heating to 1000 ꢀC
under a nitrogen atmospheꢀre. Only marginal improvement in
the thermal stability (ꢁ10 C) was noted upon postcuring to
In summary, the liquid properties of monomer 1 along with
the ability to cure at room temperature to a transparent poly-
mer with good hardness and excellent thermal and oxidative
stability demonstrate the potential of the polymers for a vari-
ety of applications. This combination of physical properties
may allow the use of polymers produced from 1 in coatings,
adhesives, and optics and potentially as a spinnable fiber for
textile applications. Additionally, depending on the reactive
SiAH sites in the silane containing curing additive used in the
hydrosilylation reaction, elastomeric materials with varying
degrees of crosslinking density and hydrolytic stability can be
readily obtained. The procedure to produce resin 1 has the
potential to be applicable to a variety of bisphenols. In subse-
quent articles, we will explore the physical and mechanical
properties of 1 and other silanes with varying structure.
ꢀ
300 C. A sample of 4c exhibited a weight retention of 95%
ꢀ
at 350 C and an overall residue of 35% remained upon heat-
ing to 1000 ꢀC under a flow of air. Similar stability results
were noted for 4a–b and 4d–e with all samples exhibiting
char yields ranging from 40 to 30%, respectively.
The hydrolytic stability of polymer 4 was assessed by soak-
ing polymer 4a and 4c in water at 25 and 100 ꢀC. After
ꢀ
soaking at 25 C for 4 days, sample 4a exhibited little notice-
able visible changes and absorbed no detectable water and
the Shore A hardness was identical to unsoaked materials.
However, 4c turned opaque and absorbed 3% water and the
hardness changed from 60 to 50. At 100 ꢀC overnight, both
samples of 4a and 4c turned opaque and became very rub-
bery and exhibited a weight loss of 5 and 9%, respectively,
and the hardness dropped significantly. This can be attrib-
uted to the hydrolysis of the SiAO bond at high tempera-
tures and high humidity with 4a being more stable due to
the higher crosslinking density which makes the water mole-
cules harder to reach the SiAO bond.
ACKNOWLEDGMENTS
The authors would like to thank the Office of Naval Research
for financial support of this project.
REFERENCES AND NOTES
1 P. R. Dvornic, R. W. Lenz, High Temperature Siloxane Elasto-
mers; Huthig & Wepf: New York, 1990.
2 M. Laskoski, T. M. Keller, J. Mater. Chem. 2009, 19, 3307–3310.
3 A. Bublewitz, J.-P. Reber, U. Nagel, U.S. Patent 2005/0171233 A1.
4 D. Troegel, J. Stohrer, Coord. Chem. Rev. 2011, 255, 1440–1459.
5 B. Marciniec, Hydrosilylation A Comprehensive Review on
Recent Advances, Advances in Silicon Science, Springer Sci-
ence, 2009; Chapter 1.
TABLE 1 Data for Polymer 4
6 M. K. Kolel-Veetil, D. D. Dominguez, C. A. Klug, T. M. Keller,
Macromol. 2009, 42, 3992–4001.
Young’s
TMSS
DMSB
Tg
(ꢀC)
Shore A
Modulus
(MPa)
7 M. K. Kolel-Veetil, T. M. Keller, J. Polym. Sci. Part A: Polym.
Chem. 2006, 44, 147–155.
(mol %)
(mol %)
Hardness
4a
4b
4c
4d
4e
100
75
50
25
0
0
214/22
212/21
216/17
212/23
212/16
70
60
60
30
n/a
2.7
2.2
2.2
1.1
n/a
8 G. Friedmann, J. Brossas, Eur. Polym. J. 1993, 29, 1197–1203.
9 M. Tsumura, J. Photo. Sci. Tech. 2009, 22, 389–390.
25
50
75
100
10 F. Guida-Pietrasanta, B. Boutevin, Inorg. Poly. Nanocomp.
Memb. 2005, 179, 1–27.
11 W. J. Zhou, H. Yang, X. Z. Guo, J. J. Lu, Polym. Degrad.
Stab. 2006, 91, 1471–1475.
526
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 523–526