Functionalized thermoplastic elastomer

Details Functionalized thermoplastic elastomer Functionalized thermoplastic elastomer

2000-02-11

2001-11-20

Mullis, Jeffrey (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S213000, C525S240000, C525S241000, C525S242000, C525S267000, C525S271000, C525S326500, C525S333300

Reexamination Certificate

active

06319990

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to functionalized polymers.
Synthetic polymers are generally characterized as either resinous or elastomeric. Historically, elastomeric polymers required chemical vulcanization before they possessed sufficient strength for utilities such as tire treads, shoe soles, rubber bands, and other elastic utilities requiring some level of strength. However, these compositions after vulcanization were no longer thermoplastic.
In the 1960s a major advance in the art occurred with the discovery and commercialization of thermoplastic elastomers. These materials possess an internal elastomeric block and a plurality of terminal aromatic blocks. On cooling from a melt, such compositions exhibit high tensile strength, high elongation, and rapid and almost complete recovery after elongation. This is attributed to the fact that in the bulk state, the aromatic end segments of these block copolymers agglomerate. At temperatures significantly below the glass transition temperature (T
g
) of the aromatic end blocks, these agglomerations (domains) act as strong, multifunctional junction points and so the copolymers behave as though they are joined in a cross-linked network.
Such polymers are non-polar and hence are sometimes not ideally suited for applications that require adhesion to polar substrates or that require compatibility with polar polymeric materials. This can be overcome by incorporating a functional group on the polymer. However, these polymers contain a large amount of aliphatic unsaturation in the diene blocks which can result in cross-lining and gellation of polymer chains during the free-radical grafting reactions used to incorporate polar functional groups. Hence, it is necessary to utilize a hydrogenation step prior to incorporating a functional group. Hydrogenation can be accomplished using any of several hydrogenation processes known in the art. For instance, the commonly used method is to employ a Group VIH metal catalyst, particularly nickel or cobalt, with a suitable reducing agent such as an aluminum alkyl to catalyze the hydrogenation. The disadvantage in this is the necessity for the additional hydrogenation and catalyst removal steps. These steps are equipment and time intensive and thereby increase the complexity and cost of producing functionalized thermoplastic-plastic elastomers. In addition, the hydrogenation catalysts are sensitive to certain poisons, making hydrogenation of polymers containing particular functional groups or coupling agent residues difficult or impossible.
Thus, it would be highly desirable to have a process by which functionalized thermoplastic elastomers could be directly produced without the necessity of a hydrogenation step.
SUMMARY OF THE INVENTION
It is an object of this invention to provide functionalized thermo-plastic elastomers without the utilization of a hydrogenation step.
In accordance with this invention a thermoplastic elastomer is prepared with an amorphous olefin or EPDM backbone and a plurality of pendant aromatic side chains and is thereafter contacted with a reactive functional monomer in the presence of a free radical initiator.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Surprisingly, it has been found that even though &agr;-olefin amorphous backbones inherently contain a regular pattern of ally side chains which are a potential source of Beta-scission, thermoplastic elastomers having such backbones can be functionalized and still retain a significant amount of strength.
Amorphous Backbone
There are two embodiments to this invention. In the first and preferred embodiment there is an all &agr;-olefin amorphous backbone. In this embodiment the backbone is made of an olefin monomer or a mixture of olefin monomers and a comonomer. The monomer is either a C
4
to C
30
&agr;-olefin (or mixtures thereof) or ethylene and a higher &agr;-olefin second monomer (higher than ethylene, i.e. C
3
and higher). As a practical matter, the second monomer will almost always be a C
3
to C
5
&agr;-olefin since there would be little point in utilizing a C
6
or higher second monomer since an amorphous backbone can be made directly from a C
6
&agr;-olefin, if desired. Broadly, however, the second monomer can be any C
3
to C
30
&agr;-olefin. The preferred monomers are hexene, octene, ethylene/propylene and ethylene/butene. When the backbone is made from a combination of ethylene and a C
3
or higher &agr;-olefin, the C
3
or higher &agr;-olefin is used in a mole ratio of 20 to 40, preferably 30 to 40, more preferably 30 to 35 percent.
There are three aspects to this first embodiment of the invention. In the first aspect, the comonomer is a 1-alkenyl compound containing a functional group to which an anionic polymer can be grafted “to” to produce a pendant graft block side chain.
Suitable comonomers are those having the formula
CH
2
═CH—CH
2
)
n
—Y
where n≧0 and Y is selected from the group including halosilane groups, hydridosilane groups, ester groups, aldehyde groups, ketones, halogens, epoxides, and phosphorous groups of the formula P—Z where Z is Cl, Br, I, F, hydrogen, ester groups, or combinations of these.
The preferred 1-alkenylhalosilane compounds which can be used in the present invention include H
2
C═CH—(CH
2
)
n
—SiX
3
where n≧0; X=halogen, R or H or combinations thereof; R is alkyl, or aryl; and at least one X must be halogen. This definition of R is in the context of a 1-alkenylhalosilane, R being used in other contexts hereinafter. Similarly X is used in another context later. H
2
C═CH—(CH
2
)
n
—SiMe
2
Cl is preferred because when the presence of ungrafted anionic polymer in the final product is undesirable, this halosilane may easily be removed from the backbone copolymer due to its high volatility.
Also preferred for the same reason are hydrosilane compounds of the formula
CH
2
═CH—(CH
2
)
n
SiH
x
R
y
where n≧0, x+y=3, x≧1, and y≦2. Most preferred compounds have these structures: CH
2
═CH—CH
2
—SiH
3
, CH
2
═CH—SiH
3
, CH
2
═CH—SiH
2
CH
3
, and CH
2
═CH—CH
2
—SiH
2
CH
3
. In the last two structures halogen may take the place of H, in which case the silanes would be halosilanes.
In the second aspect of this first embodiment, the comonomer is a vinyl aromatic compound represented by the general formula
wherein n is an integer of 0 to 20, or an alkenyl alkyl or aryl silane represented by the formula:
CH
2
═CH—(CH
2
)
n
—SiR
m
H
x
  (2)
where n is 0 or an integer of from 1 to 12; R is alkyl or aryl, preferably methyl, phenyl, or ethyl; x is 0 or 1; m is 2 or 3; and x+m 3 The most preferred alkenyl silanes for use herein are allyltrimethylsilane and allyl dimethylsilane because they are most reactive to copolymerization with &agr;-olefins. This forms a copolymer which becomes the backbone of the graft block copolymer of the present invention.
In this aspect of the first embodiment, the comonomer contains a functional group. In the case of the first formula, the benzylic carbon atom imparted by the comonomer can be deprotonated by a metallating agent such as RLi and the resulting structure behaves in a manner similar to styrene anions. Thus, while the vinyl aromatic comonomer might not normally be thought of as imparting a functional group on incorporation into the polymer chain, the benzylic hydrogen is functional to the metallating agent. In the case of the second formula, the R group can be deprotonated by the metallating agent. From this metallated functional group a monovinyl arene anionically polymerizable monomer is grown “fromr” the backbone to form pendant aromatic side chains.
In the third aspect of this first embodiment of the invention, the comonomer is an olefin capped aromatic polymer chain utilized to give aromatic side chains of sufficient length and number to form resinous or glassy domains. The comonomer is produced by anionic polymerization of a monoalkenyl aromatic compound having 8 to 20 carbon atoms with alkenyl groups of up to 3 carbon atoms attached to a benzene ring

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