Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-10-30
2003-06-17
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S343000, C525S355000, C525S359100, C526S173000, C526S204000, C526S205000, C526S213000, C526S335000
Reexamination Certificate
active
06579949
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the preparation of low hysteresis rubber by termination with a sulfur-containing reagent.
It is often desirable to produce elastomeric polymers capable of exhibiting reduced hysteresis when properly compounded with other ingredients such as reinforcing agents and then vulcanized. Such elastomers, when fabricated into components for constructing articles such as tires, vibration isolators, power belts, and the like, will manifest properties of increased rebound, decreased rolling resistance and reduced heat-build up when subjected to mechanical stress during normal use.
The hysteresis of an elastomers refers to the difference between the energy applied to deform an article made from the elastomer and the energy released as the elastomer returns to its initial, un-deformed state. In pneumatic tires for instance, lowered hysteretic properties are associated with reduced rolling resistance and reduced heat build-up during operation of the tire. These properties, in turn, result in lowered fuel consumption of vehicles using such tires and prolonged tire life. In such contexts, the property of lowered hysteresis of compounded, vulcanizable elastomer compositions is particularly significant.
Examples of such compounded elastomer systems are known to the art and are comprised of at least one elastomer (that is, a natural or synthetic polymer exhibiting elastomeric properties, such as a rubber), a reinforcing filler agent (such as finely divided carbon black, thermal black, or mineral fillers such as clay, silica and the like) and curing with a sulfur-containing vulcanizing system.
Various synthetic strategies have been developed to provide elastomers with molecular structures exhibiting reduced hysteresis. One technique is to produce elastomers of very high molecular weight. In such high molecular weight systems, the number of free, unattached molecular chain-ends per given weight in the vulcanizates made from them are reduced. Because the presence of free, unbound chain ends is believed to be a significant factor in hysteretic energy loss (because they cannot participate in the elastic recovery processes), reducing their number is believed to lead to a desirable reduction in hysteretic energy loss. A reduction in the measured tan &dgr; of the elastomer is indicative of a reduction in the hysteresis of the elastomer.
Another approach to producing elastomers with reduced hysteresis properties involves “jumping” of elastomer intermediates having a terminal functionality which is reactive under anionic polymerization conditions. Such jumping reactions join two elastomer molecules at their functional ends to produce a single molecule of much higher molecular weight. Such participation again reduces the number of free, unbound chain ends in the vulcanizate which results in low hysteretic energy loss.
It has also been recognized that carbon black, employed as a reinforcing filler in rubber compounds, should be well dispersed and separated throughout the rubber in order to improve various physical properties. One physical property that is improved by this dispersion and separation is a lowered level of hysteresis in the resultant vulcanizate. This improved dispersion may be achieved, for example, by reacting a metal terminated polydiene with a capping agent, such as a halogenated nitrile, a heterocyclic aromatic nitrogen-containing compound or a trialkyl tin halide. Additionally, it is known in the art that both ends of the polydiene chains can be capped with polar groups by utilizing functionalized anionic initiators, such as lithium amide or lithium trialkyl tin halides.
In another approach to reducing hysteresis, lithium amino magnesiate anionic polymerization initiators, stable at high polymerization temperatures, have been employed to produce polymers containing a high level of tertiary amine functionality with functional end groups derived from the initiator. Such polymers can be compounded to produce vulcanizable elastomers exhibiting reduced hysteresis properties.
It has also been known to produce modified elastomers with purely hydrocarbyl terminal functionality which are capable of conferring low hysteresis properties. For example, commonly assigned U.S. patent application Ser. No. 07/636,961 describes elastomers with tin containing end-groups derived by initiating polymerization under anionic conditions with tin-lithium compounds such as trialkyl tin (IV) lithium, that is, (alkyl)
3
SnLi groups.
Another technique is to prepare elastomer molecules with end groups capable of interacting with the reinforcing fillers, such as carbon black, present in compounded elastomer compositions. Also, such interaction with carbon black is thought to coat the aggregated carbon black and reduce formation of the carbon black network. Such interactive end groups include those derived from various metal reagents as well as those derived from polar organic reagents such as amines, amides, esters, imines, imides, ketones and various combinations of such groups. One example of functional end-capping is provided in published European Patent Application Number EP 0 316 255A2 which discloses a process for end-capping polydienes by reacting a metal terminated polydiene with a capping agent such as a halogenated nitrile, a heterocyclic aromatic nitrogen containing compound or an alkyl benzoate. Additionally, the application discloses that both ends of the polydiene chains can be capped with polar groups by utilizing functionalized initiators, such as lithium amides.
End functionalized polymers, also known as telechelic and semi-telechelic polymers, are industrially important polymers and pre-polymers in their own right. They are used for preparing segmented block copolymers and crosslinked materials and, are also useful in preparing graft copolymers.
Still other strategies aimed at preparing reduced hysteresis compounds have included high temperature mixing of the filler-rubber mixtures in the presence of selectively reactive promoters to promote compounding material reinforcement, surface oxidation of the compounding materials, and chemical modifications to the terminal end of polymers using 4,4′-bis(diethylamino)-benzophenone (Michler's ketone), tin coupling agents and the like, and surface grafting thereon. All of these approaches have focused upon increased interaction between the elastomer and the compounding materials.
Use of organolithium initiators to polymerize conjugated diene, triene, and monovinyl aliphatic and aromatic monomers is known in the art. These polymerizations proceed according to anionic polymerization mechanisms. That is, these polymerization reactions generally include the reaction of monomers by nucleophilic initiation to form and propagate a polymeric structure. Throughout the formation and propagation of this polymer, the polymeric structure is ionic or “living”. A living polymer, therefore, is a polymeric segment having at least one living or reactive end. For example, when a lithium containing initiator is employed to initiate the formation of a polymer, the reaction will produce a reactive polymer having a lithium atom at its living or reactive end.
Organolithium initiators are known in the art. Initiators which are specifically known include N-lithiohexamethyleneimine, n-butyllithium, tributyl tin lithium, dimethylaminolithium, diethylaminolithium, dipropylaminolithium, dibutylaminolithium, dialkylaminoalkyllithium, such as diethylaminopropyllithium and trialkly stannyl lithium, among others.
Chain propagation of an anionically-polymerized polymer typically ceases when all available monomer is consumed or when the living end is quenched or terminated. Typically, termination occurs in the presence of an electrophilic reagent, a terminating agent or a proton donor. Also, living polymers can spontaneously terminate because their carbanion centers decay with time. Spontaneous termination is also prevalent at higher polymerization temperatures where inter-polymer coupling likewise occurs.
The ability to an
Hergenrother William L.
Rademacher Christine M.
Ulmer James D.
Bobak Donald
Bridgestone Corporation
Dawson Robert
Palmer Meredith
Zimmer Marc S
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