1. CHEMICALLY MODIFIED EMULSION SBR IN TIRE TREADS
GEORGES THIELEN*
GOODYEAR TECHNICAL CENTER LUXEMBOURG, L-7750 COLMAR BERG
ABSTRACT
A series of Emulsion SBRs (E-SBR) with polar and nonpolar third co-monomers are studied in silica filled com-
pounds. The applied third co-monomers include polar types such as acrylonitrile (ACN), hydroxypropyl methacrylate
(HPMA) and 1-vinylpyridine (VP) and nonpolar types such as isoprene and 1,3-pentadiene. The impact of the third co-
monomers on compound reinforcement, hysteresis, abradability and viscoelastic properties is studied for single polymer
compounds as well as polymer blends with 1,4-cis-polybutadiene (cis-BR) and Natural Rubber (NR). Changes in misci-
bility of the polymer blends are studied via viscoelastic temperature sweeps and via Atomic Force Microscopy (AFM).
All blends show a miscibility behavior in agreement with Hildebrand solubility parameter predictions. The nonpolar co-
monomers lead to an increased miscibility while the polar co-monomers reduce the miscibility with cis-BR and NR.
These changes only show up in blend Tg’s and viscoelastic response and stay associated with a heterogeneous AFM
blend structure with different degrees of mixed phase compositions. The impact of the third co-monomers is more pro-
nounced in the case of cis-BR than in the case of NR blends in this study.
The preferred chemically modified ESBR is the one with 3% HPMA showing improved performance relative to
unmodified ESBR and unmodified Solution SBR (SSBR).
INTRODUCTION
With the introduction of silica technology in passenger tread applications the chemical con-
trol of filler/polymer interactions has become of key importance. Besides the control through the
silane reaction type and level, the polymer functionality plays an essential role. The majority of
efforts over the last years were made in the design of performance enhancing functionality in
solution SBRs.
However, several functionalities which are undergoing a direct hydrogen bond interaction
with silica cannot be applied during the living anionic polymerization of solution SBR, while
they can easily be introduced through copolymerization in emulsion SBRs. Hydroxylated
methacrylates and acrylates are well described as suitable third co-monomers in ESBRs for
enhancing the interaction with silica.1,2 Acrylonitrile and Vinylpyridine are other third co-
monomers in Emulsion SBRs which have been reported versus hydroxyl co-monomers.3
Synergisms in lowering compound hysteresis can be obtained when combining Emulsion SBRs
with acrylonitrile and hydroxylated methacrylate.4
EXPERIMENTAL
Different ESBR terpolymers are investigated in model recipes with a silica loading of 35
weight% and a silane loading of 8 weight% relative to silica. The elastomeric matrix is varied
covering 100 phr SBR recipes as well as SBR/cis-BR and SBR/NR recipes of blend ratios 75/25
and 50/50. Compounds were mixed in a 1100ml tangential lab mixer with two filler mixing
stages and discharge temperatures of either 160 °C.
The applied silane was Bis-(triethoxysilylpropane)disulfane (TESPD) and the high disper-
sion silica was a grade with 160 m2/g BET Nitrogen Surface area. The cis-BR was Nickel cat-
alyzed and had a cis-content of 97% and Mooney (ML4/100 °C) 50 and the natural rubber was
a technically specified grade TSR20. Compound recipes are listed in Table I.
625
* Ph: 352-81992585; Fax: 352-8199 3856; email: georges.thielen@goodyear.com

2. TABLE I
COMPOUND RECIPES
The non oil extended ESBR types of a targeted Mooney ML/4/100 °C 60 and a targeted Tg
-35 °C listed in Tables II and III have been studied.
TABLE II
EMULSION SBRS OF VARIED CO-MONOMERS
HPMA: Hydroxypropyl methacrylate (80% 2-HPMA). ACN: Acrylonitrile.
TABLE III
EMULLSION SBRS WITH VARIED ACN AND HPMA CO-MONOMER LEVELS
Viscoelastic temperature sweeps have been performed under shear at 0.1% amplitude with
a Metravib SMD2000 equipment. Atomic Force Microscopy AFM pictures were generated in
tapping mode. Insoluble rubber data were generated according to a company internal test method
using THF at room temperature for 1 day and correlate with standard bound rubber data. DSC
data were generated at a 20 °C/min heating rate. All other test data were generated applying stan-
dard test methods.
626 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

3. RESULTS AND DISCUSSION
SINGLE ESBR COMPOUND STUDIES
In the single ESBR silica compound recipes, the compound Tg determined as Tan D peak
temperature is fully related to the raw rubber Tg determined by DSC. In Figure 1 the compound
Tg is systematically shifted by +10 °C versus the raw rubber Tg due to the equipment related dif-
ferences in imposed solicitation frequency.
FIG. 1. – Single ESBR compound Tg versus raw rubber Tg for materials listed in Table II.
The viscoelastic Tan D temperature sweeps are plotted in Figure 2. The compound Tg varies
in a range of 8 °C in accordance to a rubber Tg range of 7 °C.
In case of HPMA ESBR a broadened Tan D peak response with a characteristic high tem-
perature tailing is observed in Figure 3. This tailing is associated with an increased insoluble rub-
ber fraction and might mechanistically be related to rubber chains with reduced chain mobility
in the immediate filler surrounding.
CHEMICALLY MODIFIED EMULSION SBR IN TIRE TREADS 627
FIG. 2. – Viscoelastic Tan D temperature sweeps of single ESBR silica compound recipes.

4. The peak broadening is quantified as difference between the compound Tg onset and end-
point at a Tan D amplitude of 0.2. All modified ESBRs stay within experimental error in the same
range as the unmodified ESBR with the exception of HPMA ESBR featuring a 9 °C broader Tan
D peak in Table IV. Thus HPMA is the only co-monomer leading to an increased strong interac-
tion with silica which results in an increased insoluble rubber fraction.
TABLE IV
TAN D PEAK BROADNESS OF SINGLE ESBR COMPOUND RECIPES
DUAL BLENDS WITH CIS-BR
In case of silica filled 50/50 dual blend compounds with 1,4-cis-BR important compound Tg
variations over a 30 °C range are observed. Piperylene and isoprene modified grades shift the
compound Tg towards lower values due to an increased miscibility with cis-BR. Vinyl pyridine,
HPMA and ACN modified grades lead to a reduced miscibility with cis-BR and an increased Tan
D peak temperature in Figure 4.
These changes in Tan D temperature response are still associated with a heterogeneous blend
structure determined by AFM in Figure 5. The domain size increases from ESBR-Isoprene to
unmodified ESBR, HPMA-ESBR and ACN-ESBR. The discrete domains can be expected to be
of different phase composition with the ESBR-Isoprene blend featuring the highest mixed phase
composition volume percentage with no resolved discrete viscoelastic cis-BR phase response. In
case of ACN ESBR an almost pure discrete viscoelastic cis-BR phase response remains.
628 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81
FIG. 3. — Viscoelastic Tan D temperature sweeps of HPMA ESBR
and unmodified ESBR in single ESBR silica compound recipes.

5. BR/ESBR Blend Tg diagrams have been determined by including an intermediate 25/75
BR/ESBR blend ratio. The Tg variation with blend ratio in Figure 6 is smallest for ACN-ESBR
followed by HPMA-ESBR, unmodified ESBR and ESBR-Isoprene. The blend miscibility level
accordingly increases in the indicated sequence.
CHEMICALLY MODIFIED EMULSION SBR IN TIRE TREADS 629
FIG. 4. — Viscoelastic Tan D temperature sweeps of 50/50 ESBR/cis-BR silica compound recipes.
FIG. 5. — AFM microscopy images with a 5 by 5 micron
resolution of 50/50 ESBR/cis-BR silica compound recipes.
FIG. 6. — BR/ESBR compositional Tg diagrams for silica filled compound recipes.

6. The sequence in blend miscibility level is well related to the chemical polarity of the ESBR
structures. The overall solubility parameter δ is a measure of chemical polarity and has been cal-
culated via incremental molar attraction constants by Hoy.5 From Table V it is apparent, howev-
er, that the decreased blend miscibility and increased miscibility gap observed with HPMA
ESBR are an exception to this relationship. The δ-parameter difference towards cis-BR is slight-
ly reduced for HPMA ESBR relative to unmodified ESBR and a decreased blend miscibility with
cis-BR is thus not predicted.
TABLE V
SOLUBILITY PARAMETERS FOR SELECTED ESBRS RELATIVE TO CIS-BR
Actually one has to take into account in case of HPMA ESBR the cohesive energy parame-
ters for polar systems distinguishing the dispersive, polar and hydrogen-bonding terms in the sol-
ubility parameter.6 HPMA contributes to a strong increase in the polar term of the solubility
parameter δp and thus a reduced miscibility with cis-BR is only observed in case of polar filler
systems.
IMPACT OF SILICA AND CARBON BLACK ON CIS-BR BLEND MISCIBILITY
The blend miscibility of ACN and Isoprene modified ESBR with cis-BR is independent of
the choice of carbon black or silica, while a strong dependency was observed with HPMA-
ESBR.
Indeed it could be demonstrated that the blend miscibility with cis-BR is only reduced with
HPMA ESBR in case of silica filled compounds while it stays unchanged in case of carbon black
filled compounds. The silica due to its high silanol group density and polar surface is able to
strongly interact via hydrogen bonds with the HPMA ESBR. A preferential silica interaction
occurs with the HPMA ESBR phase overall provoking a cis-BR blend miscibility level lower
than the thermodynamic equilibrium state of the blend. The reduced miscibility in presence of
silica is apparent in Figure 7 displaying the G’’ temperature sweep of a 25/75 silica filled cis-BR
blend recipe. A more pronounced G’’ response close to -100 °C is attributed to an increased vol-
ume% of the discrete cis-BR phase and the shift by +5 °C of the HPMA ESBR peak response is
indicative of a more pure highly concentrated SBR phase. At a 50/50 blend recipe the impact of
HPMA ESBR gets still more evident in Figure 8.
630 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81

7. Contrary to silica filled compounds the HPMA ESBR does not lead to a change in cis-BR
blend miscibility versus unmodified ESBR in presence of carbon black. This is in accordance
with the almost identical total δ-parameter of HPMA ESBR and unmodified ESBR. Carbon
Black interactions with HPMA ESBR are based on van der Waals Forces and thus the dispersive
term of the δ-parameter gets essential. The G’’ temperature sweeps of carbon black filled 25/75
blends with cis-BR are displayed in Figure 9. Silane addition applying various mixing conditions
did also not impact the blend miscibility and no change in the G’’temperature sweeps was detected.
CHEMICALLY MODIFIED EMULSION SBR IN TIRE TREADS 631
FIG. 7. — G’’ temperature sweeps of silica filled cis-BR/ESBR blend recipes at 25/75 blend ratio.
FIG. 8. — G’’ temperature sweeps of silica filled cis-BR/ESBR blend recipes at 50/50 blend ratio.

8. The HPMA ESBR miscibility with cis-BR can thus be displaced below its thermodynami-
cally stable state of miscibility as a consequence of a preferential interaction with silica. This cis-
BR blend miscibility effect is opposite to the silica impact previously reported for unmodified
ESBR. The miscibility of unmodified ESBR can indeed be increased above its thermodynamic
equilibrium state by applying a reactive silica mixing.7.
DUAL BLENDS WITH NR
The impact of co-monomers on the blend miscibility with Natural Rubber (NR) is less pro-
nounced than with cis-BR. In each case a heterogeneous blend structure appears and compound
Tg’s of the enriched SBR phase vary little with the NR/ESBR blend composition. The Tg shift
is less pronounced and the miscibility is lowest with ACN ESBR, followed by unmodified ESBR
and HPMA- ESBR at an equal level. The isoprene modified ESBR finally shows the highest mis-
cibility related Tg increase with a Tg shifting over blend ratio which is comparable to SBR 1502
which has a much lower styrene content of 23.5% (Figure 10).
Out from the G’’ temperature sweeps in Figure 11 it gets apparent that phase separated pure
NR phases of unchanged G’’ peak maximum location exist in all cases. The ESBR phase com-
positions are of varying purity changing from pure to mixed composition in the order ACN >
HPMA, unmodified > Isoprene in accordance with a reduction in d-parameter difference of the
blends.
632 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81
FIG. 9. — G’’ temperature sweeps of carbon black filled cis-BR/ESBR blend recipes at 25/75 blend ratio.

9. ACN AND HPMA CO-MONOMER LEVEL EFFECTS
The impact of the co-monomer level was investigated for HPMA and ACN at 0.5, 1, 2, 3 and
5 weight%. Variations in filler/polymer interaction, hysteresis, abrasion and reinforcement have
been investigated in single SBR recipes and 25/75 BR/SBR recipes and are reported for the sin-
gle SBR recipe (Figures 12 to 15).
CHEMICALLY MODIFIED EMULSION SBR IN TIRE TREADS 633
FIG. 10. — NR/ESBR compositional Tg diagrams for silica filled compound recipes.
FIG. 11.— G’’ temperature sweeps of silica filled NR/ESBR blend recipes at 50/50 blend ratio.

10. 634 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81
FIG. 12. — Insoluble Rubber of pure ESBR silica compound recipes
in function of ACN and HPMA co-monomer level.
FIG. 13. — Tan D of pure ESBR silica compound recipes in function of ACN and HPMA co-monomer level.
FIG. 14. — DIN abrasion volume loss of pure ESBR silica
compound recipes at 3% HPMA and ACN co-monomer level.

11. Insoluble Rubber is indicative of an increased silica interaction with the rubber matrix and
translates into a reduced hysteresis (Tan D 100 °C) and DIN abrasion.
As already observed in case of the impact on the compound glass transition peak, the ACN
functionality does not contribute to an increased filler/polymer interaction over the entire ACN
range from 0.5 to 5 weight%. Hysteresis does consequently not improve, but slightly increases;
DIN abrasion stays in the range of the unmodified control for all ACN ESBR samples.
In case of HPMA all properties progressively improve while the improvement levels off at
3 weight%.
The Tan D peak high temperature tailing in Figure 16 which is associated with the volume
fraction of the bound rubber phase gets progressively more pronounced until 3% HPMA and then
levels off in good agreement with the properties reported in Figures 12 to 15.
Figure 17 finally compares the viscoelastic behavior of SBR ACN and SBR HPMA at 3
weight% co-monomer level in a 25/75 BR blend silica recipe.
CHEMICALLY MODIFIED EMULSION SBR IN TIRE TREADS 635
FIG. 15. — DIN abrasion volume loss of silica compound recipes in function of
HPMA co-monomer level.
FIG. 16. — HPMA ESBR related Tan D Peak broadness evolution of 25/75 cis
-BR/ ESBR silica compound recipes in function of HPMA co-monomer level.

12. While the miscibility level with cis-BR is comparable based on the Tan D Peak locations,
the increased filler/polymer interaction clearly shows up in a highly broadened TanD peak
response in case of HPMA.
HPMA ESBR CANDIDATE PERFORMANCE
The preferred chemically modified ESBR with 3% HPMA has been compared to unmodi-
fied ESBR and unmodified SSBR of comparable Tg and styrene. The HPMA ESBR compares
favorably in respect to DIN abrasion, Tan D at -10 °C and 60 °C as expressed in Figure 18 in rel-
ative performance ratings.
636 RUBBER CHEMISTRY AND TECHNOLOGY VOL. 81
FIG. 17. — Tan D temperature sweep evolution of 25/75 cis-BR/ ESBR
silica compound recipes at 3 weight% HPMA and ACN level.
FIG. 18. — Performance Ratings of ESBR 3% HPMA versus unmodified
ESBR and SSBR in a 25/75 silica cis-BR/SBR blend recipe.

13. CONCLUSIONS
All blends show a miscibility behavior in agreement with Hildebrand solubility parameter
predictions. The unipolar co-monomers lead to an increased miscibility while the polar co-
monomers reduce the miscibility with cis-BR and NR. These changes only show up in blend Tg’s
and viscoelastic response and stay in each case associated with a heterogeneous AFM blend
structure with different degrees of mixed phase compositions. The impact of the third co-
monomers is more pronounced in case of cis-BR than in case of NR blends in this study.
The miscibility of HPMA ESBR with cis-BR was investigated in further detail and actually
is only reduced in presence of silica and does not change in presence of carbon black. The
decreased miscibility is a consequence of a more pronounced silica interaction with the HPMA
ESBR phase and is actually a displacement from the thermodynamic blend equilibrium state. A
reduced blend miscibility with cis-BR is observed with ACN and HPMA levels above 1 weight%
in ESBR. The change in miscibility through ACN is observed, however, with silica as well as car-
bon black.
With increasing HPMA content the silica rubber interaction progressively increases as can
be shown via bound rubber content and via characteristic high temperature tailings in the TanD
temperature sweeps. ACN and the other co-monomers do not lead to a change in silica rubber
interaction. The increased silica interaction through HPMA reflects also in improved hysteresis
and wear which reach their optimum at 3 weight% HPMA.
The preferred chemically modified ESBR is the one with 3% HPMA showing improved per-
formance relative to unmodified ESBR and even unmodified SSBR.
ACKNOWLEDGEMENT
The author wishes to thank the Goodyear Tire and Rubber Company for permission to pub-
lish this work.
REFERENCES
1H. Colvin, M. Senyek (to Goodyear Tire & Rubber Company) U.S. Patent 6,455,655B1, September 24, 2002.
2H. Colvin, M. Senyek (to Goodyear Tire & Rubber Company) U.S. Patent 6,512,053B1, January 28, 2003.
3S. Hofmann, R. Tietz, V. Monroy, “Effects Of Chemical Functionalization Of Polymers On Tire Silica Compounds:
Emulsion Polymers, ” Paper presented at a meeting of Rubber Division, ACS, Paper 63A, Cleveland, OH, October
16-18, 2001.
4G. Thielen, (to Goodyear Tire & Rubber Company) U.S. Patent 6,716,925 B2, April 6, 2004.
5E.A. Grulke, Solubility Parameter Values, In “Polymer Handbook,” 4th Edition, Brandup, E.H. Immergut, and E. A.
Grulke, Eds., John Wiley & Sons, NY, NY, 1999, VII, p. 675-714.
6A.F.M. Barton, CRC Handbook Of Solubility Parameters And Other Cohesion Parameters, 2nd Edition, CRC Press,
Boca Raton, Fla., 1991.
7G. Thielen, Kautsch. Gummi Kunstst. 60, 389 (2007).
[ Paper 58, presented at the Fall Rubber Division, ACS, Meeting (Cleveland)
October 16-18, 2007, revised May 2008 ]
CHEMICALLY MODIFIED EMULSION SBR IN TIRE TREADS 637