Block copolymer composition, process for producing the same,...

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

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C525S098000, C525S099000

Reexamination Certificate

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06534593

ABSTRACT:

TECHNICAL FIELD
This invention relates to poly(aromatic vinyl)/polyisoprene block copolymer compositions suitable for pressure-sensitive adhesive use, a process for producing the same, and pressure-sensitive adhesive compositions containing such block copolymer compositions.
BACKGROUND ART
Conventionally, various block copolymers including polystyrene/polyisoprene block copolymers have been used as base polymers for pressure-sensitive adhesive compositions. Moreover, it is also known that radial polystyrene/polyisoprene block copolymers represented by the following formula are used for such purposes.
(S−I)
n
X
wherein S is a polystyrene block, I is a polyisoprene block, n is a natural number of 3 or greater, and X is a residue of a coupling agent.
Various coupling agents are used for the production of radial block copolymers. From the viewpoint of reactivity, bond stability, stabilized supply, cost and the like, tetrafunctional silicon compounds are among the most preferred coupling agents. Accordingly, several attempts have been made to synthesize a styrene/isoprene block copolymer for pressure-sensitive adhesive use by using a tetrafunctional silicon compound as a coupling agent (see, for example, Japanese Patent Laid-Open No. 266156 /'89, Japanese Patent Laid-Open No. 138547/'95, and Published Japanese Translation of PCT International Publication No. 511260/'97). In these attempts, however, the resulting copolymer scarcely contains a four-branch polymer in spite of the use of a tetrafunctional coupling agent, and its principal component is a three-branch polymer.
It is disclosed in Japanese Patent Laid-Open No. 337625/'96 that a radial polystyrene/polyisoprene block copolymer can be obtained by reacting polyisoprene with a silicon tetrachloride coupling agent, and then adding thereto a cyclohexane solution of a separately formed polystyrene/polyisoprene block copolymer and a coupling accelerator comprising 1,2-dimethoxyethane. However, this radial polystyrene/polyisoprene block copolymer is an unsymmetrical block copolymer consisting of two polyisoprene arms and two polystyrene/polyisoprene block copolymer arms.
It is disclosed in Published Japanese Translation of PCT International Publication No. 511260/'97 that a block copolymer composition having a four-branch structure as a principal component can be obtained by introducing a small amount of polybutadiene chains at the polymerizing end of the diblock polymer and then reacting the resulting copolymer with a tetrafunctional coupling agent to form a four-branch polymer. However, its adhesive properties are markedly reduced by the influence of the polybutadiene chains, and the resulting pressure-sensitive adhesive composition fails to have satisfactory performance.
WO98/18840 discloses a poly(aromatic vinyl)/polyisoprene block copolymer comprising 5 to 50% by weight of a four-branch polymer and 50 to 95% by weight of a diblock polymer, and a pressure-sensitive adhesive composition containing this block copolymer. However, from the viewpoint of the balance between tack at low temperatures and holding power, there is yet room for improvement in this poly(aromatic vinyl)/polyisoprene block copolymer.
An object of the present invention is provide a radial poly(aromatic vinyl)/polyisoprene block copolymer composition having a well-balanced combination of tack at low temperatures and holding power and exhibiting high values therefor, a process for producing the same, and a pressure-sensitive adhesive composition using the same.
DISCLOSURE OF THE INVENTION
The present inventors made intensive investigations with a view to accomplishing the above object. As a result, it has now been found that a poly(aromatic vinyl)/polyisoprene block copolymer composition comprising (a) 1 to 34% by weight of a diblock polymer, (b) 34 to 99% by weight of a four-branch polymer, and (c) 0 to 50% by weight of at least one branched polymer selected from the group consisting of a two-branch polymer and a three-branch polymer can readily be obtained by preparing a poly(aromatic vinyl)/polyisoprene block copolymer comprising a diblock copolymer having a poly(aromatic vinyl) block A and a polyisoprene block B joined to each other, and then reacting it with a coupling agent having a functionality of 4 or higher, and that a pressure-sensitive adhesive agent comprising this poly(aromatic vinyl)/polyisoprene block copolymer composition and a tackifier resin provides an excellent adhesive.
Thus, according to the present invention, there is provided a poly(aromatic vinyl)/polyisoprene block copolymer composition comprising 1 to 34% by weight of a diblock polymer represented by the following General Formula 1 and referred to as component (a), 34 to 99% by weight of a four-branch polymer represented by the following General Formula 2 and referred to as component (b), and 0 to 50% by weight of at least one branched polymer selected from the group consisting of a two-branch polymer represented by the following General Formula 3 and a three-branch polymer represented by the following General Formula 4, and referred to as component (c), wherein the poly(aromatic vinyl)/polyisoprene block copolymer composed of component (a), component (b) and component (c) has a weight-average molecular weight (Mw) of 260,000 to 500,000, and the poly(aromatic vinyl)/polyisoprene block copolymer has a poly(aromatic vinyl) block content of 5 to 24% by weight.
A
1
-B
1
  General Formula 1
wherein A
1
is a poly(aromatic vinyl) block having a weight-average molecular weight (Mw) of 9,000 to 20,000, and B
1
is a polyisoprene block.
(A
2
-B
2
)
4
X
2
  General Formula 2
wherein A
2
is a poly(aromatic vinyl) block having a weight-average molecular weight (Mw) of 9,000 to 20,000, B
2
is a polyisoprene block, and X
2
is a residue of a coupling agent having a functionality of 4 or higher.
(A
3
-B
3
)
2
X
3
  General Formula 3
wherein A
3
is a poly(aromatic vinyl) block, B
3
is a polyisoprene block, and X
3
is a residue of a coupling agent having a functionality of 2 or higher.
(A
4
-B
4
)
3
X
4
  General Formula 4
wherein A
4
is a poly(aromatic vinyl) block, B
4
is a polyisoprene block, and X
4
is a residue of a coupling agent having a functionality of 3 or higher.
Moreover, according to the present invention, there is also provided a process for producing a poly(aromatic vinyl)/polyisoprene block copolymer composition, the process comprising the steps of (1) bringing an organolithium initiator into contact with an aromatic vinyl monomer to form a poly(aromatic vinyl) block A having an active polymerizing end, (2) adding isoprene so as to form an A-B block copolymer in which a polyisoprene block B having an active polymerizing end is directly joined to the poly(aromatic vinyl) block A, and (3) reacting the A-B block copolymer with a coupling agent having a functionality of 4 or higher in the presence of a coupling accelerator so as to convert 34 to 99% by weight of the A-B block copolymer into the four-branch polymer represented by General Formula 2.
Furthermore, according to the present invention, there is also provided a pressure-sensitive adhesive composition comprising the poly(aromatic vinyl)/polyisoprene block copolymer composition and a tackifier resin.
EMBODIMENTS OF THE INVENTION
[(a) Diblock Polymer]
The diblock polymer used as component (a) in the present invention is a diblock polymer represented by the following General Formula 1, and a residue of a coupling agent may be added to an end of the polyisoprene block B
1
.
A
1
-B
1
  General Formula 1
wherein A
1
is a poly(aromatic vinyl) block and B
1
is a polyisoprene block.
No particular limitation is placed on the type of the aromatic vinyl monomer used for the synthesis of the diblock polymer. Specific examples thereof include styrene, &agr;-methylstyrene, vinyltoluene and vinylnaphthalene, and styrene is preferred. These aromatic vinyl monomers may be used in admixture of two or more.
No particular limitation is placed on the pro

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