The present invention generally relates to the preparation of low hysteresis rubber.
The hysteresis of an elastomer refers to the difference between the energy applied to deform the elastomer and the energy recovered as the elastomer returns to its initial, undeformed state. In many industries, it is often desirable to produce elastomeric compounds exhibiting reduced hysteresis when properly compounded with other ingredients, such as reinforcing agents, and then vulcanized. Such elastomers, when compounded, fabricated, and vulcanized into components for constructing articles such as tires, power belts, and the like, will manifest properties of increased rebound and reduced heat build-up when subjected to mechanical stress during normal use. In pneumatic tires, lowered hysteresis properties are associated with reduced rolling resistance and heat build-up during operation of the tire. As a result, lower fuel consumption is realized in vehicles using such pneumatic tires.
Compounded elastomer systems are known in the art and are comprised of at least one elastomer, a reinforcing filler agent (such as carbon black or mineral fillers such as clay, silica, and the like), and a vulcanizing system. Notably, interaction between the elastomer molecules and the reinforcing filler agent(s) is known to affect hysteresis.
It has been recognized that hysteresis and other physical properties of compounded elastomer systems can be improved by ensuring good dispersion of carbon black throughout the elastomer component. In particular, it has been recognized that individual carbon black aggregates should be well dispersed in order to minimize the contact between them. By preparing elastomers with end groups capable of interacting with reinforcing fillers such as carbon black, dispersion of individual carbon black aggregates is stabilized, reducing interaggregate contacts and thereby reducing hysteresis. Thus, increased interaction between elastomer chain ends and reinforcing fillers will tend to decrease hysteretic losses.
Thus, there exists a need in the art for increasing interaction between elastomer molecules and reinforcing fillers within a compounded elastomer system. More particularly, there exists a need in the art for a terminator that provides elastomer molecules with end groups that interact with the functionality of carbon black and other reinforcing fillers. There also exists a need in the art for a process for terminating polymers with such desired end groups.
In the present invention, lithium-initiated polymers are terminated with oxazoline compounds. Useful oxazoline compounds may be selected from organic halide oxazoline compounds and branched or unbranched vinyl oxazoline compounds.
When organic halide oxazoline compounds are employed, the carbon-lithium chain end of the propagating polymer reacts with the halide provided by the oxazoline compound, and the polymer is terminated with the organic oxazoline.
When a branched or unbranched vinyl oxazoline compound is employed, the vinyl oxazoline compound is inserted between the propagating polymer and the lithium atom, thereby effectively terminating further polymer propagation with chemical units other than vinyl oxazoline compounds or, more broadly, monomers that will polymerize with a substituted acrylate anion, such as, for example, esters of methacrylic acid, acrylic acid, cyanoacrylic acid and the like.
The oxazoline ring of these terminators interacts with carbon black, and the resulting functional polymers therefore exhibit reduced hysteresis in cured, compounded rubber, when compared to unterminated, yet otherwise identical, controls.
Generally, the present invention provides a method of forming an oxazoline functionalized polymer. The method includes the steps of forming a solution of one or more anionically polymerizable monomers in an alkane solvent, and polymerizing the monomers in the presence of a lithio-containing initiator so as to produce a living lithium polymer as is known in the art. The living lithium polymer is then terminated with an oxazoline compound according to the formula (I): 
wherein R1 to R5 are selected according to the following criteria:
R1 is selected from the group consisting of:
an organic halide according to the following formula (II): 
wherein each R6 may be the same or different and is selected from the group consisting of a branched or linear C1-C20 alkyl moiety, a C3-C20 cycloalkyl moiety, a C6-C20 aryl moiety, and a C7-C20 alkylaryl moiety, R7 is selected from the group consisting of a branched or linear C1-C20 alkylene moiety, a C4-C20 cycloalkylene moiety, and a C6-C20 alkylarylene moiety, and X is a halogen;
a branched or unbranched vinyl moiety according to the following formula (III): 
wherein R8 is selected from the group consisting of hydrogen, a branched or linear C1-C20 alkyl moiety, a C3-C20 cycloalkyl moiety, a C6-C20 aryl moiety, and a C7-C20 alkylaryl moiety;
a moiety according to formula (IV): 
wherein each R6 may be the same or different and is selected according to the same criteria set forth in formula (II); and
hydrogen; and
R2-R5 may be the same or different and are selected from the group consisting of:
hydrogen;
an organic halide, xe2x80x94R7xe2x80x94X, wherein R7 is as already defined, and X is a halogen; and
a branched or linear C1-C20 alkyl moiety, a C3-C20 cycloalkyl moiety, a C6-C20 aryl moiety, and a C7-C20 alkylaryl moiety, with the proviso that if R1 is selected from either an organic halide according to formula (II) or a vinyl moiety according to formula (III), R2-R5 are selected from hydrogen, a branched or linear C1-C20 alkyl moiety, a C3-C20 cycloalkyl moiety, a C6-C20 aryl moiety, and a C7-C20 alkylaryl moiety; and if R1 is selected from either hydrogen or a moiety according to formula (IV), one of R2-R5 is selected from an organic halide, xe2x80x94R7xe2x80x94X, the other R2-R5 groups are selected from the group consisting of hydrogen, a branched or linear C1-C20 alkyl moiety, a C3-C20 cycloalkyl moiety, a C6-C20 aryl moiety, and a C7-C20 alkylaryl moiety.
The present invention also provides compounds according to the following formula: 
wherein X is a halogen, and each Z is the same and is selected from the group consisting of hydrogen and a methyl group.
As mentioned, it has been found that the oxazoline ring of the terminators disclosed herein beneficially interact with carbon black to reduce hysteresis in rubbers compounded with carbon black. Thus, the present invention also provides a method for producing a tire having reduced hysteresis. This method includes terminating a lithium-initiated rubber with an oxazoline compound; and compounding the oxazoline-terminated rubber with carbon black, wherein the oxazoline compound employed to terminate the lithium-initiated rubber is selected according to formula (I) under the criteria as set forth above with respect to formula (I).