Grafted near-gelation polymers having high damping properties

Details Grafted near-gelation polymers having high damping properties Grafted near-gelation polymers having high damping properties

2000-06-05

2002-11-05

Woodward, Ana (Department: 1711)

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

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S506000, C524S514000, C524S515000, C524S517000, C524S522000, C525S064000, C525S066000, C525S069000, C525S071000, C525S074000, C525S077000, C525S078000, C525S079000

Reexamination Certificate

active

06476117

ABSTRACT:

FIELD OF THE INVENTION
The present invention is generally directed to thermoplastic elastomers and compositions containing such thermoplastic elastomers that are useful for damping. More particularly, the thermoplastic elastomers of this invention are multi-block polymers that contain hard and soft segments. The soft segments include near gelation polymers that impart damping properties to the thermoplastic elastomer over a wide range of temperatures and frequencies.
BACKGROUND OF THE INVENTION
Damping is the absorption of mechanical energy, such as vibrational or sound energy, by a material in contact with the energy source. Damping or mitigating the transmission of the vibrational energy from sources such as motors, engines, and the like can be desirable. When viscoelastic materials are used in damping applications, they absorb and convert energy to heat. Such materials preferably are effective over a wide range of temperatures and frequencies.
The viscoelastic nature of materials can be mathematically represented by the formula G*=G′+iG″ where G* is the complex shear modulus, G′ is the elastic or storage modulus, G″ is the viscous or loss modulus and i=the square root of −1. The effectiveness of a viscoelastic material for damping purposes can be quantified by measuring its viscoelastic response to a periodic stress or strain. Results of dynamic mechanical tests are generally given in terms of G′ and G″, the latter of which is directly related to the amount of mechanical energy that is converted to heat, or in other words, damping.
The ratio of the loss modulus G″, to the elastic modulus G′, is referred to as tan &dgr; which is a measure of the ability of a given material to dissipate mechanical energy into heat versus the purely elastic storage of mechanical motion during one cycle of oscillatory movement. Tan &dgr; can be measured by a dynamic analyzer, which sweeps a range of frequencies at a fixed temperature and repeats that sweep of frequencies at several other temperatures. From the generated data, a master curve of tan &dgr; versus frequency can be developed.
Tan &dgr; can be adjusted or broadened by taking advantage of the glass transition temperature of several materials within a temperature range. One example of this is a composition including resins cured in sequential fashion by a single BrØnsted acid catalyst, which activates an epoxy resin component and then catalyzes cyanate trimerization into poly(triazines). The composition provides a glass transition damping peak around 100° C. and is understood to be heat stable over a temperature range of about 0° to at least 300° C.
Another exemplary composition includes a soft crosslinked elastomeric binder containing microscopically discrete segments of multiphase thermoplastic elastomeric polymer that have at least two polymeric phases (i.e., an initial linear or lightly linked polymeric phase and a second polymeric phase in the form of discrete domains dispersed within the initial polymeric phase). The initial polymer phase provides a glass transition damping peak around 10° to 70° C.
Another known damping material includes an interpenetrating polymer network having a soft polyurethane component and a hard poly(vinyl ester) component which are formed in the presence of one another and cured at room temperature. The interpenetrating polymer network is taught to have an acoustic damping factor in excess of 0.2 over a temperature range of from about 15° to about 85° C., with a glass transition damping peak at about 55° C.
Another known vibration damping composition includes an acrylate-containing thermoset resin incorporating an interpenetrating network of polymerized epoxy and a poly(acrylate). This resin is said to have a glass transition temperature in the range of about −2° to about 200° C. at 1 Hz.
Although numerous compositions are known for damping, there is a need for improved damping compositions that exhibit a high degree of damping over a wide range of temperatures and frequencies without involving glass transition peaks. Enhancing hysteresis (tan (&dgr;)) by using the super position of glass transition peaks is not desirable because the modulus of the material drops dramatically at or about the glass transition temperature.
SUMMARY OF INVENTION
Briefly, the present invention provides a thermoplastic elastomer including a multi-block polymer that includes randomly distributed hard and soft segments connected by covalent bonds. The hard segments include polymeric chains of a crystalline polyalkylene, while the soft segments include a near-gelation polymer. The hard and soft segments are connected by covalent bonds.
In another aspect, the present invention provides a thermoplastic elastomer produced by allowing a functionalized, near-gelation polymer to react with a functionalized, crystalline polyalkylene and allowing for a time sufficient to form the elastomer.
In a further aspect, the present invention provides a method of making a thermoplastic elastomer. In the method, a composition including a liquid, crosslinkable, functionalized polymer having low or no unsaturation is subjected to the action of a crosslinking agent so as to form a near-gelation elastomer that includes a crosslinked polymer. Thereafter, a covalent bond is allowed to form between at least one functional group on each of the near-gelation elastomer and a functionalized crystalline polyalkylene. The near-gelation elastomer has a physical state relative to the gelation point of the crosslinked polymer defined by
0≦|(r−r
g
)/r
g
|≦0.5
in which r is the weight ratio of the crosslinking agent to the functionalized prepolymer, and r
g
is the weight ratio of the crosslinking agent to the functionalized prepolymer at the gelation point of the crosslinked polymer.
DETAILED DESCRIPTION
Thermoplastic elastomers that contain at least one block of a near-gelation polymer have been found to exhibit excellent damping characteristics over a wide range of temperatures and frequencies. These thermoplastic elastomers have a tan &dgr; which is greater than or equal to about 0.4 from about −30° to about 50° C. and which preferably is substantially constant throughout this temperature range. Additionally, these thermoplastic materials are elastomeric at room temperature and are thermally processable as thermoplastics at a temperature above 100° C. The thermoplastic elastomers can be soft and possess a Shore A hardness that is less than or equal to about 40.
The thermoplastic elastomers of this invention are multi-block polymers that include at least one soft, near-gelation polymeric segment and at least two hard, crystalline polyalkylene segments connected by covalent bonds. These elastomers can contain more than one soft segment and more than two hard segments. Moreover, they are not necessarily linear, resulting from the non-linear nature of the near-gelation polymer. In general, the near-gelation polymer includes many chain ends, at least two of which are linked to crystalline, polyalkylene hard segments. Depending on the number of hard and soft segments, these polymers can include a three-dimensional, interconnected polymeric network. The thermoplastic elastomer molecules provide an interconnected array of numerous branched soft segments connected to numerous crystalline, polyalkylene hard segments. The hard and soft segments of the thermoplastic elastomers of this invention are believed to be phase separated with the hard segments forming crystallized domains at room temperature.
The nature of the hard and soft segments can be understood with reference to the individual components used to create them. In general, the thermoplastic elastomers are prepared by linking a functionalized near-gelation polymer to a functionalized crystalline polyalkylene through the functional groups on each. As discussed in greater detail hereinbelow, the hard and soft segments can be linked through a direct reaction between the respective functional groups or thro

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