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Synthesis and properties of ethylene isoprene and ethylene isoprene styrene block polymers.

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Die Angewandte Makromebkulare Chemie 21 (1972) 17-23 (Nr. 286)
From the Roy C. Ingersoll Research Center, Borg-Warner Corporation
Des Plaines, Illinois
Synthesis and Properties of Ethylene, Isoprene and
Ethylene, Isoprene, Styrene Block Polymers
By JOHNCARL FALK*and R. J. SCHLOTT
(Eingegangenam 22. April 1971)
SUMMARY:
A new method is described to introduce pure blocks of ethylene, isoprene, and
styrene into polymer systems composed of these moieties. This method involves the
selective catalytic hydrogenation of 1,4-butadiene-1,4-isopreneand 1,4-butadiene1,4-isoprene-styreneco and terpolymers.toform ethylene-1,4-isopreneand ethylene1,4-isoprene-styreneco and terpolymers. The properties of these polymer systems
are discussed as a function of composition and degree of polymerization. A useful
feature of this technique is the preparation of ABA type thermoplastic elastomers.
ZUSAMMENFASSUNG :
Eine neue Methode zur Herstellung von Blockpolymeren aus Athylen-, Isoprenund Styrolblocken wird beschrieben. Durch selektive katalytische Hydrierung werden 1,4-Butadien-1,4-Isopren-Copolymere und 1,4-Butadien-l,4-Isopren-StyrolTerpolymere zu Athylen-1,4-1sopren-Copolymerenund Athylen-1,4-1sopren-StyrolTerpolymeren umgesetzt. Die Eigenschaften dieser Polymeren werden in AbhZingigkeit von der Zusammensetzung und vom Polymerisationsgrad diskutiert. In praktischer Hinsicht ist die Herstellung von MA-Blockpolymeren als thermoplastische
Elastomere von Bedeutung.
Introduction
The literature contains numerous examples of ethylene, isoprene copolymerizations using coordination type catalysts, sometimes referred to as ZIECILER
type catalysts. For example SUMINOE~
has copolymerized ethylene and isoprene
using a triethylaluminium titanium tetrachloride catalyst. This work and other
typical workz-10 describes the production of random copolymers or macroblock copolymers. Styrene may be easily incorporated into these systems affording terpolymers of ethylene, isoprene and styrene. Pure di or tri block copolymers of ethylene, isoprene or ethylene, isoprene, and styrene have not been produced in these systems.
* Author to whom all correspondence should be addressed.
17
J. C. FALK
and R. J. Scmom
In this paper we wish t o report a convenient synthesis of ethylene, isoprene
or ethylene, isoprene, and styrene block co and terpolymers having a rigorously
defined block sequence. The effect of block length hand sequence on physical
properties is discussed.
Experimental
Synthesis
A solution of 15 g (0.28 moles) of butadiene in 700 ml of cyclohexane under a dry
nitrogen atmospherewas treated with 0.3mmoles of s-butyl1ithium.Thereactionmixture was kept a t 50°C for 16 hrs. Dry, freshly distilled isoprene, 15 g (0.22 moles),
was added and the reaction mixture was kept a t 50 "C for 16 hrs. The third block was
made by adding 15 g (0.28 moles) of butadiene or 15 g (0.144 moles) of styrene to the
reaction mixture. After 16 hrs. at 50°C the living polymer was quenched with isopropanol. 1,4-Butadiene-1,4-isoprene-1,4-butadiene
or 1,4-butadiene-1,4-isoprenestyrene block polymers were produced. Infrared analysis showed the microstructure
of the butadiene blocks to contain 43% cis 1,4,49% trans 1,4 and 8% 1,2 structure.
The isoprene block was predominantly cis 1,4. Hydrogenation catalyst was added
to this solution, and the hydrogenation was carried out immediately.
Hydrogenation
Ethylene-1,4-isoprene-ethyleneor ethylene-1,4-isoprene-styreneblock polymers
were prepared by the selective hydrogenation of the butadiene moieties in 1,4-butadiene-1,4-isoprene-1,4-butadieneand 1,4-butadiene-1,4-isoprene-styreneblock polymers according to the method of F A L K A
~ ~1,4-butadiene-l,4-isoprene-1,4-buta.
diene or a 1,4-buta&ene-l,4-isoprene-styreneblock polymer, 20.0 g, was dissolved in
1500 ml of cyclohexane and placed with 0.3 mole percent of a cobalt 2-ethylhexanoate triethylaluminium catalyst having an aluminium-cobalt ratio of 3.5/1 in a
two-liter reactor thermostated a t 50 "C. Hydrogen ww bubbled through the reactor
at a constant hydrogen pressure of 50 psi throughout the hydrogenation. The reaction was carried out until the infrared spectrum of an aliquot was free of absorption
due to butadiene unsaturation, ca. 60 min reaction time. The polymer solvent mixture was washed with dilute aqueous acid to remove catalyst residue, then precipitated in isopropanol and dried a t 60 "C under vacuum.
Results and Discussion
The ethylene-1,bisoprene and ethylene-l,4-isoprene-styrene
block and random polymers were prepared by the low pressure catalytic hydrogenation of co
and terpolymers of 1,4-butadiene, 1,4-isoprene, and styrene in a selective manner :
18
Ethylene Isoprene Block Polymers
These selective hydrogenations were effected with the triethylaluminium cobalt 2-ethylhexanoate catalyst system described by Falkll. The substrate butadiene, isoprene, and styrene polymers were prepared by sequential anionic polymerization in cyclohexane using s-butyllithium to initiate the reaction. Thus,
anionic polymerization of butadiene affords living poly-l,4-butadiene having
) 90% 174-configuration.Addition of isoprene gave a living AB block copolymer which could be quenched with isopropanol or further reacted with butadiene or styrene to give ABA or ABC block co and terpolymers. Alcohol quenching
followed by selective hydrogenation produced ethylene-l,4-isoprene-ethylene
or ethylene-1,4-isoprene-styrene polymers.
As indicated in Table 1, the selective hydrogenation of the butadiene moieties
in random 1,4-butadiene-174-isoprene
copolymers gives ethylene-1,4-isoprene
copolymers with soft rubbery characteristics. Variation of the degree of polymerization and the ratio of ethylene to 1,4-isoprene in the random copolymers
had very little effect on the rubbery character of the copolymers.
Molecular weights indicated throughout the paper are those calculated for the
substrate 1,4-butadiene, 1,4-isoprene, and styrene block polymers from the
Entry
Type
qsp/cb
Yield
(Psi)
Tensile strength
Substratec
Ultimate
Elongation MW
(Psi)
(YO)
1
20 EIa
0.69
2
66 E I
1.03
260
410
580
3
66 E I
-
370
1290
730
120
4
80 E I
1.39
510
1350
670
100
too soft
50
60
(W/W) ethylene (E), 80% (W/W) isoprene (I)
In deoalin at 135OC, 0.1 g/dl.
Calculated molecular weight of the butadiene, isoprene copolymer substrate.
a 20%
b
C
19
J. C. FALK
and R. J. SCHLOTT
monomer/initiator ratio. Lack of suitable methods prevented our ascertaining
whether degradation occurred with these mild hydrogenations. Hydrogenations
using the same catalyst in analogous systems in these laboratories show little
degradation. The rsp/c values, measured on the ethylene, 1,4-isoprene and styrene block polymers may reflect only a trend.
Aggregation of the ethylene, 1,4-isoprene moieties into separate blocks forming ABA systems, Table 2, produces polymers, a t a high degree of polymerization, with high ultimate tensile strength coupled with low tensile yield, Entries 1-5.
Table 2.
Entry
1
2
3
4
5
6
7
8
9
10
11
a
b
C
d
Physical properties ethylene-l,4-isoprene-ethylene
block polymers as a
function of degree of polymerization.
Type
vsp/cb
Yield
(Psi)
66EIEa
66EIE
66EIE
66EIE
66EIE
50EIE
55EIE
75EIE
80EIE
60EzIEc
75EzIE
0.62
0.94
1.25
1.26
1.38
0.54
0.59
1.04
1.25
1.29
0.66
700
700
760
730
780
320
560
840
730
580
860
Tensile strength
Substrated
Ultimate
Elongation MW
(Psi)
(YO)
680
2 200
2 200
1700
1900
790
1 200
2 100
1300
1600
980
570
600
730
650
580
625
700
690
540
730
300
90
120
18.0
210
250
80
120
120
100
100
80
66 EIE contains 66% ethylene A blocks.
In decalin at 135OC, 0.1 g/dl.
The initial A block contains twice aa much polyethylene as the second.
Calculated molecular weight of the butadiene, isoprene copolymer substrate.
Variation of the ethylene-l,4-isoprene ratio has little effect on the tensile
yield and percent elongation, however, the ultimate tensile strength is greatly
influenced, Entries 2 and 6-9. The block copolymers having the maximum ultimate tensile strength have between 66 and 75% polyethylene composition. Increasing the length of one of the A blocks in an ABA block copolymer a t the
expense of the other has a slight negative effect on the ultimate tensile strength
with little effect on tensile yield or percent elongation, Entries 10 and 11. The
Ethylene Isoprene Block: Polymers
copolymers listed in Table 2 all exhibited elastic recoveries between 85 and
93yo and can be considered thermoplastic elastomers.
In a similar fashion 1,Cbutadiene-l,4-isoprene-styrene
polymers may be
selectively hydrogenated to ethylene-1,.l-isoprene-styrene terpolymers. The
requisite 1,Cbutadiene-1,Cisoprene-styrene terpolymers are prepared by the
sequential addition of charges of isoprene and styrene to a living poly-1,Cbutadiene. Each segment is allowed to completely polymerize prior to addition of
the next.
As indicated in Table 3 these polymers have soft rubbery characteristics. As
the degree of polymerization is increased, no change.is noted in the tensile
yield and percent elongation, with a slight increase in ultimate tensile strength,
Entries 1-5. At a constant degree of polymerization, as the ethylene and styrene
blocks are increased at the expense of the interior isoprene block, an increase in
tensile yield and ultimate tensile strength is observed while the percent elongation remains relatively constant, Entries 2 and 6-10. The soft rubbery characteristics of the polymers are retained regardless of the degree of polymerization or
composition.
Some recently developed thermoplastic elastomers owe their properties to
their ABA block structurelo. These copolymers consist of rigid thermoplastic
Entry
Type
qSp/c&
Yield
(Psi)
1
2
3
4
5
6
7
8
9
10
66 EIStb
66 EISt
66 EISt
66 EISt
66 EISt
45 EISt
55 EISt
66 EISt
75 EISt
85 EISt
0.96
1.28
1.35
1.37
1.62
1.01
1.26
1.28
1.28
-
630
710
810
800
600
180
440
710
970
1400
Tensile strength
Substratec
Ultimate
Elongation MW
(Psi)
(YO)
860
1200
1 300
1 200
1 200
370
640
1200
1100
1600
440
520
610
470
660
510
510
520
300
310
90
120
150
180
250
120
120
120
120
120
In decalin at 135"C, 0.1 g/dl.
33% Polyethylene A block, 33% polystyrene C block.
c Calculated molecular weight of the butadiene, isoprene, styrene terpolymers sub-
a
b
strate.
21
J. C. FALK
and R. J. S C H L O ~
A blocks and soft, rubbery B segments, and exhibit behavior similar to that of
crosslinked structures. Typical examples of such linear thermoplastic elastomers are those described by MORT ON^^, S Z W A R and
C ~ ~Fm14,
,
including styrene-1,4-butadiene-styrene,ethylene-(ethylene,propylene)-ethylenel5,and ethylene-(ethylene,butene-l)-ethylene ABA block copolymers.
In our system, ABA block copolymers also exhibit thermoplastic behavior, as
shown in Table 2. Ethylene-1&isoprene-ethylene block copolymers having compositions of 66 to 75% ethylene, are tough, clear rubbery materials, while on
either side of this range a decrease in ultimate tensile strength occurred resulting
in soft rubbery polymers. The ethylene-1,4-isoprene-styreneABC block terpolymers retained their soft rubbery characteristics throughout the degree of polymerization and composition ranges studied in Table 3. This may result from the
incompatibility of the ethylene and styrene A and C blocks, if ABA block elastomers depend for their rubbery properties solely upon the aggregation of the rigid glassy domains which effectively act as network junctions, as suggested by
MORTONand others.
We have described a new way to introduce blocks of ethylene, 1,4-isoprene,
and styrene in a well defined manner into polymer systems. This method involves the selective catalytic hydrogenationof 1,4-butadiene-l,4-isoprene-l,Cbutadiene and 1,4-butadiene-1,4-isoprene-styrene block polymers to ethylene-1,4isoprene-ethylene and ethylene-1,4-isoprene-styreneblock polymers. A useful
feature of this selective hydrogenation technique is the preparation of ABA
thermoplastic elastomers. The ethylene-l,4-isoprene-ethylene
block polymers
described in this paper exhibit thermoplastic elastomeric properties. With low
yields, high ultimate tensile strength, good elongation and elastic recovery, these polymers are consistent with the ASTM definition of elastomersl6: ,,A substance that can be stretched at room temperature to at least twice its original
length and, after having been stretched and the stress removed, returns with
force to approximately its original length in a short time."
Acknowledgements
The authors would like to express their appreciation to Dr.D. F. HOEQand
Dr. J. F. PENDLETON
for their encouragement and many suggestions and to
G. MATULAfor technical assistance.
1
2
3
22
T . SUMINOE,
Chem. high Polymers Tokyo 20 (1963) 467.
US-Pat. 3244678(April 5, 1966), Inv. : S.TOCKER.
Canadian Pat. 780523 (March 12, 1968),Invs.: H. L. HASSELL,
et al.
Ethylene Iaqvrene Block Polymers
T. SUMINOE,
et al., Chem. high Polymers Tokyo 20 (1963) 262.
Netherl. Pat. 6507644 (December 17, 1965).
6 Brit. Pat. 950067 (February 19, 1964), Inv.: 0. W. BERKE.
7 M. STEINBERQ,
et al., “Ind. Uses of Large Radiation Sources”,Proc. Cod., Salzburg, Austria, 1 (1963) 121.
Belg. Pat. 623941 (October 23, 1962), Inv.: B. VANDER
HAEQHEN.
9 US-Pat. 893462 (April 11, 1962), Inv.: S. TOCKER.
10 L. J. FETTERS
and M. MORTON, Macromolecules 2 (1969) 453, and references
cited therein.
11 J. C. FALK,
J. Polymer Sci., in press.
1 2 M. MORTONand L. J. FETTERS,
Macromolecules Reviews, Volume 2, Interscience, New York, p. 71.
13 M. SZWARC,
“Carbanions Living Polymers and Electron-Transfer Processes”,
Interscience, New York, 1968 p. 73ff.
14 J. C. FALK,
Macromolecules 4 (1971) 152.
15 South Afric. Pat. 665994 (August 26, 1966), Invs.: H.L. HASSELL
and A. W.
4
5
*
SHAW.
16
ASTM Special Technical Bulletin No. 184, 1956, p. 42.
23
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