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
2002-07-09
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...
C525S314000, C525S316000, C525S271000
Reexamination Certificate
active
06417270
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.
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 strength, while the triblock polymer provides the composition with its elastomeric properties. One process for preparing such composition is to physically blend the triblock 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 final composition of the mixture extremely difficult. Better adhesive properties generally 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 triblock, 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 a triblock interpolymer and a diblock interpolymer. The process includes polymerizing vinyl aromatic monomer in an inert hydrocarbon solvent in the presence of an anionic catalyst system until substantially complete conversion to a living vinyl aromatic polymer has occurred. A conjugated diene monomer is added to copolymerize with the living vinyl aromatic polymer. A first terminating agent is then added in sufficient amount to terminate at least a portion of but less than all of the product of step (b), thereby forming the diblock interpolymer. A second portion of vinyl aromatic monomer is added, then a second terminating agent, thereby forming the triblock interpolymer. Optionally, at least one of the first terminating agent and the second terminating agent includes a functional terminating agent.
In another aspect, a block copolymer composition is provided. The composition includes a first block interpolymer of the general formula A
1
B
1
A
2
and a second block interpolymer of the general formula A
1
B
1
. A
1
and A
2
independently represent a poly(vinyl aromatic) block and B
1
represents a poly(conjugated diene) block. At least one of the block interpolymers is terminated by a functional group selected from the group consisting of hydroxyl, alkoxysilane, amine, and carboxyl.
In another aspect, an adhesive composition is provided. The adhesive composition includes 15-40% by weight of a polymer composition as previously described, 40-70% by weight of a compatible tackifying resin and 5-30% by weight of a plasticizing oil.
In another aspect, a process is provided for preparing a diblock/triblock polymer composition in which at least one of the diblock and triblock polymers is functionalized. The process includes polymerizing one of a vinyl aromatic monomer and a conjugated diene monomer in an inert hydrocarbon solvent in the presence of a first portion of an anionic catalyst system until substantially complete conversion to a first living polymer has occurred. The first living polymer contributes a first block of a triblock interpolymer and a first block of a diblock interpolymer. The first block of each of the triblock and diblock interpolymers each includes either a first vinyl aromatic polymer or a first diene polymer. The other of the vinyl aromatic monomer and the conjugated diene monomer is added, allowing formation of a midblock of the triblock interpolymer, and a second block of the diblock interpolymer. At least one of a functional terminating agent and a protic terminating agent is added in a sufficient amount to terminate less than all of the product of step. A second portion of one of a vinyl aromatic monomer and a conjugated diene monomer is added followed by at least the other of the functional terminating agent and the protic terminating agent, forming the triblock interpolymer and the diblock interpolymer.
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.
By “living polymer,” it is meant that a polymer, prepared by anionic polymerization, has active terminals (e.g., lithium terminals) which enable the polymer to undergo further polymerization reactions or to be terminated through a suitable terminating process.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process of the present invention includes the sequential steps of:
(1) polymerizing a vinyl aromatic monomer A
1
such as styrene, in an inert hydrocarbon solvent in the presence of a suitable catalyst until substantially complete conversion to a living vinyl aromatic polymer;
(2) adding a conjugated diene monomer B, such as butadiene, and allowing the conjugated diene monomer to polymerize until substantially complete conversion;
(3) adding a terminating agent to terminate a portion of the living polymers;
(4) adding a second portion of a vinyl aromatic monomer A and allowing it to polymerize until substantially complete conversion; and
(5) adding a terminating agent to terminate the remainder of the living polymers.
The terminating agent used in step (3) is preferably a functional terminating agent, and the terminating agent used in step (5) is preferably a protic terminating agent, although a functional terminating agent may be used in both steps (3) and (5) or any other combination of the two terminating agents may be used.
The functional terminating agent includes a functional group (i.e, a group other than H), which is selected to add functionality to 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%, an
Graves Daniel F.
Wollum Mark H.
Asinovsky Olga
Burleson David G.
Firestone Polymers LLC
Seidleck James J.
Skerry Ann
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