Filled PO elastomers SI revised version 13 May 2016

Filler Reinforced Elastomers Based on Functional Polyolefin Prepolymers
Ning Ren,a Henry Martinez,b Megan E. Matta,b Kim L. Walton,c Jeffrey C. Munro,c
Deborah K. Schneidermanb, and Marc A. Hillmyerb,*
a
Department of Chemical Engineering and Materials Science, University of
Minnesota, 421 Washington Avenue SE, Minneapolis, MN 55455-0132, USA
b
Department of Chemistry, University of Minnesota, 207 Pleasant Street SE,
Minneapolis, MN 55455-0431, USA
c
The Dow Chemical Company, Freeport, TX 77541
Supporting Information
Materials
Cis-Cyclooctene (COE) (Fisher Scientific) was purified by distillation. Grubbs second
generation (G2) catalyst, ethyl vinyl ether, and maleic acid were purchased from
Sigma-Aldrich and used as received. Trimethylolpropane tri(2-methyl-1-aziridine
propionate) (TAz, 95% purity) and Silica-supported platinum catalyst were obtained
from PolyAziridine LLC and Dow Chemical Company respectively and used as
received. 3-Ethyl-1-cyclooctene was synthesized according to the previous report.1
Tetrahydrofuran and cyclohexane were purified with an M. Braun solvent purification
system and degassed with argon flow for 15min before used. Two types of fillers,
Aerosil R-812 (hydrophobic fumed silica, surface area 260 m2/g, produced by Evonik)
and V7H (low structure carbon black, surface area 112 m2/g, produced by Cabot)
were used as received.
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Characterization
1
H and
13
C NMR spectra were recorded on a Bruker AV500 spectrometer at room
temperature using CDCl3 as solvent. Number-average molecular weight (Mn) was
determined by 1H NMR end group analysis. Differential Scanning Calorimetry was
performed on a TA Instruments Discovery DSC. Thermal gravimetric analysis was
performed on a TA Instruments Q500 TGA. Density of filled elastomers was
determined by a density gradient column (isopropanol/ethylene glycol) at room
temperature (25 °C). Tensile, tear and hysteresis tests of filled elastomers were
conducted on a Trapezium X tensile tester (SHIMADZU) according to the ASTM
D1708 standard. Scanning electron microscopy was performed on HIACHI 4700 FESEM.
Dynamic Mechanical Temperature Analysis was performed by torsion test on a
rectangular geometry (13mm x 50 mm x 1mm) using an ARES-G2 rheometer (TA
Instruments). During the experiment the temperature was increased from -90 to
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200 °C at a rate of 5 °C/min. The frequency and strain were constant at 6.28 rad/s and
0.05%, respectively. Viscosity measurements were performed at 25°C with an 8 mm
parallel plate geometry using an ARES-G2 rheometer (TA Instruments). Room
temperature (25°C) oscillatory frequency sweeps and strain sweeps were performed in
tension (using a RSA G2 rheometer with rectangular strips (13mm x 50 mm x 1mm)),
torsion (ARES-G1 rheometer with rectangular strips (13mm x 50 mm x 1mm)), and
shear mode (ARES-G1 rheometer with a 8mm parallel plate geometry). Frequency
sweeps were conducted at a strain of 0.05%, while strain sweeps were conducted at a
frequency of 1 Hz.
We note that the results of the oscillatory rheology experiments were somewhat
inconsistent. First, the modulus value in shear is underestimated (by almost an order
of magnitude) compared to the modulus values in torsion and tension. This may be an
indication that the samples were slipping on the surface of the plate. Importantly,
when tests were conducted in torsion mode, the modulus values during frequency and
strain experiments were similar to the room temperature plateau modulus values
observed by DMTA (also in torsion mode). Unfortunately, in this mode several of the
samples were observed to slip or tear near the grip, therefore the relative trends
observed may not be entirely accurate or reproducible.
Additionally, for tests
conducted with this geometry the upper range of strain was limited to ~2-3%. In
tension mode, the upper strain value was also limited, however in the shear mode,
much larger strain ranges could be accessed.
With regards to angular frequency tests, tension mode and shear mode gave similar
relative trends, however as noted previously, the modulus values for shear are much
lower than expected. Additionally, the room temperature results for sample xPHEt-
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Si20 (both strain and frequency sweeps) are anomalous and do not match the expected
trend of increasing modulus with filler content. Because the results of oscillatory tests
in shear, strain, and torsion modes are not in good agreement with each other we are
hesitant to draw definitive conclusions about the nature of polymer-filler and fillerfiller interactions in filler reinforced xPHEt samples on the basis of these tests.
However, for the interested reader, we include a brief discussion of the possible
explanations for the shear oscillatory data (both strain and frequency sweep
experiments) below.
Shear Frequency Sweeps at Room Temperature
The storage moduli of the prepolymers as a function of frequency were
evaluated in shear mode. For all samples, modulus values of the samples had a low
frequency dependence, consistent with previous reports. This indicates the existence
of filler-polymer interactions that influence the movement of the chain segments on
the surface of the filler aggregates.2,3 As suggested in our samples, at low loading the
carbon black filled samples seem to have stronger filler-polymer interactions whereas
the silica samples seem to have stronger filler-filler interactions2,3,4. Both samples
with fumed silica and carbon black had a higher storage moduli as compared to LSRs
at room temperature, which suggests that for the silicone elastomer, the apparent
molar mass between crosslinks or filler content is higher than in our materials.
Payne Effect
One well-known behavior of a filled elastomer with filler-filler interactions is the
Payne effect, which is the drop in modulus at small strain amplitudes.5,6 In shear
mode this was clearly observed in the silica filled elastomers. Figure S6 (top) shows
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the room temperature oscillation strain sweep study on the fumed silica reinforced
elastomers. For the sample with no filler reinforcement, the storage modulus was
invariant with strain. As the filler content was raised, however, the modulus of the
samples dropped with increasing oscillation strain so that the sample with 30 wt% of
silica filler the effect was significant. This behavior is consistent with the existence of
a filler-filler network in the filled elastomers. In contrast with the silica filled
elastomers, the strain sweep experiment on carbon black filled elastomers did not
indicate an observable Payne effect until the carbon black content reached 30 wt%
(Figure S6 bottom). This supports the morphological evidence that the carbon black
filler disperses more easily into the polymer matrix and filler-filler networks between
carbon black particles only appears at much higher loadings. We did not observe this
effect in tension or torsion modes, however, we note that the maximum strain was
limited by the instrument for both.
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Figure S1. Viscosity of xPHEt-silica mixture and xPHEt-carbon black mixture before
crosslinking. Measurements performed at 25 °C with 8 mm parallel plate geometry.
S6
Figure S2. Viscosity of xPHEt-filler mixture and LSR before crosslinking.
Measurements performed at 25 °C with 8 mm parallel plate geometry.
Figure S3. DSC traces of xPHEt with fumed silica (top) and carbon black (bottom)
2nd Heating cycle. Ramp rate of 10 °C/min.
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S8
Figure S4. TGA traces of xPHEt with fumed silica (top) and carbon black (bottom).
Ramp rate of 10 °C/min under N2.
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Figure S5. Shear angular frequency sweep (0.05 % strain, 25 °C, parallel plates) of
crosslinked PHEt with fillers (top: silica, bottom: carbon black) using circular parallel
plates. The modulus is artificially lowered with this geometry, because the crosslinked
samples do not adhere to the plate geometry at lower temperatures.
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Figure S6. Shear angular frequency sweep (0.05 % strain, 25 °C, parallel plates) of
crosslinked elastomers and a commercially available liquid silicon rubber (20−30 %
silica filler according to the manufacturer).
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Figure S7. Torsion angular frequency sweep (0.05 % strain, 25 °C, rectangular films)
of crosslinked PHEt with fillers (top: silica, bottom: carbon black). Both xPHEt-CB30
and xPHEt-Si30 were noticeably torn near the grips during the torsion test.
Figure S8. Torsion oscillation strain sweep (6.28 rad/s, 25 °C, rectangular film) of
xPHEt with fumed silica (top) and carbon black filler (bottom). N.B. Because sample
XPHEt-CB5 tore on the edge of the grip, it is likely that the modulus values are under
estimated.
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Figure S9. Tension frequency sweep (0.05 % strain, 25 °C, rectangular film
geometry) of crosslinked PHEt with fillers (top: silica, bottom: carbon black.)
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Figure S10. Tension Strain sweep (1 Hz, 25 °C, rectangular film) of crosslinked
PHEt with fillers (top: silica, bottom: carbon black).
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x
Hex
+
y
+ HO
G2, THF
OH
O O
H 2, Pt (10 wt%)/SiO2
HOOC
45oC, 20h
Hex
HOOC
80 oC, 24 h, cyclohexane
Hex
x
y
x
COOH
y
COOH
Scheme S1. Synthesis of carboxy-telechelic prepolymer PH75 via ROMP followed
by hydrogenation.
Figure S11. 1H NMR characterization of the prepolymer before and after
hydrogenation.
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Figure S12. Dynamic mechanical thermal analysis of crosslinked PH75 filled with
silica filler.
Figure S13. Viscosity of prepolymer-silica mixture before crosslinking.
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Table S1. Filler content and thermal properties of silica reinforced crosslinked PH75.
Sample ID
Filler Type
Filler Content (wt %)
xPH75
Tg (°C)a
Td (°C)b
̶64
336
xPH75-Si5
Aerosil R-812
5
̶59
343
xPH75-Si10
Aerosil R-812
10
̶59
352
xPH75-Si20
Aerosil R-812
20
̶60
360
a
Determined by DSC (second heating cycle) at 10 °C min-1. b 5% weight loss
determined by TGA at 10 °C min-1 in N2.
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Table S2. Mechanical properties of silica filler reinforced crosslinked PH75.a
Tensileb
Sample
a
Tearc
Hysteresisd
Cycle 1 (%) Cycle 2 (%)
εb (%)
σTS (MPa)
E (MPa)
N/mm
xPH75
150±10
1.1±0.1
2.5±0.1
0.31, 0.32
xPH75-Si5
220±40
1.2±0.1
xPH75-Si10
199±8
2.9±0.2
2.1±0.7
0.80, 0.85 23.7, 22.1
8.8, 8.2
xPH75-Si20
220±43
6.1±1.3
3.4±0.2
1.75, 1.59 43.5, 47.9
15.9, 16.3
7.4
0.84±0.06 0.63, 0.67 18.4, 19.6
5.0
8.9, 12.7
Mechanical properties measured on ASTM D1708 micro-tensile bars. b Measured at
69 mm/min, at least 4 tensile bars were tested for each sample. c Measured at 100
mm/min, 2 bars were tested for each sample. d Measured at 60 mm/min, strains no
greater than 50% of the elongation at break, 2 bars were tested for each sample.
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(4) Aranguren, M. I.; Mora, E.; Macosko, C. W. Compounding Fumed Silicas into
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