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
2001-05-16
2002-11-05
Seidleck, James J. (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...
C525S088000, C525S089000, C525S09200D, C525S095000, C525S098000
Reexamination Certificate
active
06476131
ABSTRACT:
TECHNICAL FIELD
This invention relates to self-reinforced rubbery compositions. These rubbery compositions comprise a rubbery matrix having glassy thermoset domains dispersed therein with covalent bonding between the rubbery matrix and the thermoset domains. The invention also relates to a method for making these compositions.
BACKGROUND OF THE INVENTION
It is desirable for rubbers used in severe dynamic applications, such as tires, to possess minimal hysteresis loss to provide low rolling resistance and low running temperature. Rubbers however, must be somewhat hysteretic in order to exhibit resistance to crack growth, crack propagation, and abrasion. Generally, when an elastomer is deformed, part of the input energy is stored elastically in the chains and is available as a driving force for fracture (i.e., will be released upon crack growth), while the remainder of the energy is dissipated through molecular motions into heat.
At high crosslink levels, when hysteresis loss is typically low, chain motions become quite restricted and the “tight” network cannot dissipate much energy. As a result, these networks, may suffer from brittle fracture at low elongation. Rubbers exhibiting high hysteresis loss, which typically have low crosslink levels, can have high tear strength at room temperature. These rubbers, however, are unsuited for dynamic applications because the substantial heat generation and concomitant temperature rise that occurs during these applications weakens the rubbers. Therefore, the art has generally sought to provide rubbers for dynamic applications that exhibit low hysteresis at small strains and become highly hysteretic at high strains.
One approach has been to disperse particulate filler within the rubber. This creates a rubber having hard domains of particulate filler dispersed within a soft rubber matrix. The addition of particulate fillers tends to reduce abrasion and crack growth rates by increasing high strain modulus and energy dissipation at high strains. The incorporation of particulate filler, however, also increases hysteresis loss at small strains. This results in an unwanted increase in power consumption and heat generation. Therefore, there is a desire in the art to provide reinforcement within a rubber matrix while maintaining low hysteresis loss at small strain.
Limited bonding between rubber and carbon black may be one source of undesirable, low strain hysteresis loss. Much effort has been made to try to lower hysteresis and enhance reinforcement by increasing the interaction of carbon black with rubber. Approaches have included heat treatment of carbon black/rubber mixes, functionalization of carbon black and the diene rubber, and the addition of a carbon black/rubber coupling agent.
More success has been achieved in enhancing filler/rubber interaction in the case of silica-filled rubber. By using a silane coupling agent, e.g., bis-(3-triethoxysilylpropyl)-tetrasulfane, with an extended high temperature mixing cycle, tire tread compounds reinforced with silica can exhibit reduced rolling resistance, while maintaining good wet skid and abrasion resistance.
The approach herein to creating a morphology of hard domains dispersed in a rubbery matrix includes thermodynamic phase separation. The concept of thermodynamic phase separation has been used to prepare many elastomers where the end blocks are thermoplastic. SBS (polystyrene-b-polybutadiene-b-polystyrene), SIS (polystyrene-b-polyisoprene-b-polystyrene), SEBS (styrene-b-ethylene butylene diene-b-styrene), SNBS (styrene-b-nitrile-b-styrene), SAS (styrene-b-acrylic-b-styrene), SCS (styrene-b-chloroprene-b-styrene), and SEPS (styrene-b-ethylene propylene diene-b-styrene) tri-block copolymers are examples. The phase separated polystyrene domains are a few hundred angstroms in size. These elastomers have high hardness, high strength, and high extensibility.
These elastomers, however, are unsuitable for high dynamic loading applications, such as tires, because the end block polystyrene is, by design, a thermoplastic elastomer that creeps and weakens quickly as temperature is increased. It has been found that these problems can be remedied by transforming the end blocks into hard glassy thermosets during the final molding of the elastomers. This structure mimics, in many ways, particulate filled rubber in that both contain non-hysteretic, temperature insensitive, hard domains dispersed within an elastomer matrix. These mesophase separated tri-block elastomers, however, all include rubber chains that are linked to hard domains while in particulate filled compositions the rubber chains either do not interact or interact weakly with the filler.
While attempts have been made to control domain sizes and the degree of bonding between hard domains dispersed within a rubber matrix, the art has not provided a facile means or device by which this can be accomplished. This is especially true where the monomers, pre-polymers, or copolymers are non-polar such as the precursors for hydrocarbon rubbers.
SUMMARY OF INVENTION
It has now been found that the benefits realized by incorporating reinforcing fillers within polymeric compositions can be achieved by a polymeric composition of matter that includes an elastomeric matrix having dispersed therein reinforcing domains that are chemically bound to the elastomeric matrix. These polymeric compositions may be referred to as self-reinforced elastomeric compositions.
In general the present invention provides a self-reinforced polymeric composition of matter comprising a plurality of hard domains dispersed throughout an elastomeric matrix, wherein the plurality of hard domains are formed by thermodynamic phase separation and selective crosslinking of at least one thermosettable domain block of a polymeric precursor and are substantially bonded to the elastomeric matrix.
The present invention also includes a method for producing a self-reinforced polymeric composition having glassy thermoset domains disbursed in an elastomeric matrix comprising the steps of selecting a thermodynamically separable polymeric precursor having at least one thermosettable domain block and at least one matrix block, and selectively crosslinking the at least one thermosettable domain block of the polymeric precursor with substantially no crosslinking of the at least one matrix block.
DETAILED DESCRIPTION OF THE INVENTION
The self-reinforced rubbery compositions have glassy thermoset domains dispersed within a rubbery matrix. The thermoset domains are chemically bound to the rubbery matrix, which may be slightly crosslinked. More particularly, the rubber compositions are di-block, tri-block, or star-block copolymers that contain at least one thermoset block. The other blocks remain uncrosslinked or are lightly crosslinked. Thus, the at least one crosslinked block provides the thermoset domains and the other uncrosslinked or lightly crosslinked blocks provide the rubbery matrix. Optionally, other additives may be present in the rubbery compositions including those additives typically employed in rubber compositions, as well as those that may provide desirable characteristics to the self-reinforced rubbery compositions.
The glassy thermoset domains are irreversibly crosslinked and preferably have a high crosslink density sufficient to provide thermoset domains having high glass transition temperature. Preferably, the glass transition temperature of these thermoset domains should be greater than about 100° C. and even more preferably greater than about 150° C.
The glassy thermoset domains are mesophase separated from the rubbery matrix in which they are dispersed. Mesophase refers to phases that are less than about 100 nanometers in size and preferably about 10 to 90 nanometers in size.
The rubbery matrix can include any rubbery polymer. Non-limiting examples of rubber polymers include those deriving from conjugated diene monomers and copolymers of conjugated diene monomers and vinyl aromatic monomers.
The rubbery polymers preferably have a glass transition temperature below about −25° C. an
Hamed Gary
Kelley Frank
Quirk Roderic
Asinovsky Olga
Renner Kenner Greive Bobak Taylor & Weber
Seidleck James J.
The University of Akron
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