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
2001-01-09
2002-03-19
Mullis, Jeffrey C. (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...
C525S180000, C525S340000
Reexamination Certificate
active
06359075
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to polymerizations, specifically to a method for preparing a combination of di-block and tri-block copolymers in a single reaction vessel, and will be described with particular application thereto.
BACKGROUND OF THE INVENTION
Blends of styrene-butadiene diblock and styrene-butadiene-styrene tri-block interpolymers have a variety of applications. In an adhesive composition, the diblock polymer provides tack, while the triblock polymer provides the composition with its elastomeric properties. One process for preparing such a composition is to physically blend the tri block and the diblock copolymers which have been prepared independently. However, such a process requires a large blending capacity and is therefore undesired. Moreover, it will be appreciated that the separate preparation of the diene diblock and triblock copolymers makes the control of the composition of the mixture extremely difficult. Better adhesive properties result by having identical molecular weights of the styrene blocks in the diblock and triblock polymers. When blending a triblock with a diblock interpolymer, it is difficult, if not impossible to achieve this optimal ratio.
Another method of forming diblock triblock compositions involves partial coupling of live diblock species. Suitable coupling agents include reactive halogen compounds, such as, for example, dimethyl dichlorosilane, silicon tetrachloride, methylene bromide, phosphorus trichloride, or divinyl benzene. This method can achieve matching of the polystyrene molecular weights in the diblock and elastomer, if a solvent is used in which the polystyrene is completely soluble. If the polystyrene is insoluble in the solvent (for example, hexane), the polystyrene maximum molecular weight is limited. For acceptable adhesive properties, it is desirable to exceed this maximum molecular weight.
Another method of forming diblock/triblock compositions is by using a multiple catalyst charge and by staggered addition of the monomers and deactivation of a portion of the growing polymer chains before or during addition of a subsequent monomer. For example, a high diblock TPE can be formed by charging a lithium catalyst with styrene and allowing polymerization, followed by further addition of the catalyst and butadiene. Once this has polymerized, a further charge of styrene is added. The resulting compositions, however, exhibit poor adhesion to stainless steel and polypropylene, and have low cohesive tensile strength.
The present invention provides a new and improved block copolymer blend, process of forming, and an adhesive composition incorporating block copolymer blend, which overcomes the above-referenced problems and others.
SUMMARY OF THE INVENTION
Briefly, the present invention provides a process for preparing a polymer composition which includes diblock and triblock copolymers. The process includes polymerizing vinyl aromatic monomer in an inert hydrocarbon solvent in the presence of a first anionic catalyst system until substantially complete conversion to a living vinyl aromatic polymer has occurred. A conjugated diene monomer is added and allowed to copolymerize with the living vinyl aromatic polymer to form a living diblock polymer including a first block which is substantially of the first vinyl aromatic polymer and a second block which is substantially of a conjugated diene polymer. A chain transfer agent is added, which terminates at least a portion of the living diblock polymer and forms a second anionic catalyst system. A conjugated diene monomer is added and allowed to copolymerize with the unterminated living portion of the diblock polymer and self polymerize with the second anionic catalyst to form a living conjugated diene polymer. A vinyl aromatic monomer is then added, and allowed to copolymerize with the living polymers to form the diblock and triblock copolymers.
In another aspect, a process of forming a composition which includes a diblock polymer and a triblock polymer is provided. The process includes polymerizing a first monomer in a suitable solvent in the presence of a first anionic catalyst system then adding a second monomer and allowing copolymerization with the first monomer to form a living diblock polymer. A chain transfer agent is added in sufficient amount to terminate only a portion of the living diblock polymer to form the diblock polymer and form a second anionic catalyst system capable of catalyzing polymerization of the second monomer. A second portion of the second monomer is added and allowed to copolymerize with the living diblock polymer and with the second ionic catalyst system. A second portion of the first monomer is then added to form the triblock polymer.
In other aspects, the invention provides a polymer composition and an adhesive composition which include the polymer compositions thus formed.
The following definitions apply hereinthroughout unless a contrary intention is expressly indicated:
An “interpolymer” is a polymer comprising mer units derived from two or more different monomers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A triblock/diblock polymer blend is particularly suited to use in an adhesive composition. The polymer blend preferably includes a styrene-butadiene-styrene elastomer and a styrene butadiene diblock copolymer. These are preferably formed in a single reactor from multiple charges of vinyl aromatic (e.g., styrene) and conjugated diene (e.g., butadiene) monomers, using an anionic, living catalyst system. A chain transfer agent, such as hexamethylene imine or other cyclic or secondary amine, is added partway through the process. The chain transfer agent functions both as a termination agent for the diblock and an initiator for starting another polymer chain.
The process of the present invention is carried out in a suitable solvent, which may be cyclic or aliphatic. In one embodiment, the process of the present invention includes the sequential steps of:
(1) polymerizing a vinyl aromatic monomer A in an inert hydrocarbon solvent, such as cyclohexane in the presence of a suitable live catalyst system until substantially complete conversion to a “living” polymer has occurred;
(2) adding a conjugated diene monomer B, and allowing the conjugated diene monomer to copolymerize with the living vinyl aromatic polymer until substantially complete conversion has occurred;
(3) terminating a portion of the living polymer chains with a chain transfer agent;
(4) adding a second portion of a conjugated diene monomer B′, and allowing the conjugated diene monomer to polymerize until substantially complete conversion;
(6) adding a second portion of a vinyl aromatic monomer A′, and allowing the vinyl aromatic monomer to polymerize until substantially complete conversion; and
(7) quenching the living polymer chains by adding at least one of a functional terminating agent and a protic terminating agent.
By living polymer, it is meant that the polymer is prepared by anionic polymerization and has active terminals (e.g., lithium ion terminals) which enable the polymer to undergo further polymerization reactions or to be terminated through a suitable terminating process.
The functional terminating agent includes a functional group (i.e, a group other than H), which is selected to add functionality to the polymers of the resulting diblock/triblock blend.
The protic terminator removes residual catalyst (lithium, in the case of an organolithium catalyst) from the interpolymers formed, and thereby prevents further reaction of the copolymers. Where both a functional terminating agent and a protic terminating agent are used, the protic terminating agent is preferably used after the functional terminating agent.
After the polymerization has been terminated, the product can be isolated, e.g., by drum drying, steam stripping, or flash evaporation.
By the term “substantially complete conversion,” it is meant that the polymerization reaction is allowed to proceed in each step until at least 90%, more preferably, at least 95%, and most pr
Graves Daniel F.
Wollum Mark H.
Bridgestone/Firestone Inc.
Burleson David G.
Mullis Jeffrey C.
Skerry Ann
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