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
2000-11-30
2002-07-30
Mullis, Jeffrey (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...
C525S333300, C525S338000, C525S332100
Reexamination Certificate
active
06426390
ABSTRACT:
The present invention is directed to a composition of a hydrogenated block copolymer of a vinyl aromatic monomer and a conjugated diene monomer.
BACKGROUND OF THE INVENTION
Various hydrogenated block copolymer compositions have been disclosed in previous applications, such as in copending applications Ser. No. 09/330,520 and Ser. No. 09/330,663, filed Jun. 11, 1999. Additionally, fabricated articles produced from such hydrogenated block copolymers have been disclosed in copending applications Ser. Nos. 09/575,063 and 09/575,062, filed May 19, 1999. However, a combination of good impact strength, processability and surface appearance is difficult to achieve in some applications of these polymers, such as in extruded sheet.
Therefore, there remains a need for hydrogenated block copolymer compositions having a superior balance of impact strength, processability and surface aesthetics which can be advantageously applied in extruded sheet applications.
SUMMARY OF THE INVENTION
It has been surprisingly discovered that an excellent balance of impact strength, processability and surface aesthetics can be obtained in a composition comprising a hydrogenated block copolymer, wherein the hydrogenated block copolymer comprises a hard segment phase volume of at least two distinct blocks of hydrogenated polymerized vinyl aromatic monomer, herein referred to as hydrogenated vinyl aromatic polymer block, and a soft segment phase volume of at least one block of hydrogenated polymerized conjugated diene monomer, herein referred to as hydrogenated conjugated diene polymer block, wherein the hydrogenated block copolymer is further characterized by:
a) a sufficient soft segment phase volume such that a lamellar morphology is achieved,
b) a total number average molecular weight (Mn
t
) of from 35,000 to 65,000; and
c) a hydrogenation level such that each hydrogenated vinyl aromatic polymer block has an aromatic hydrogenation level of greater than 90 percent and each hydrogenated conjugated diene polymer block has a hydrogenation level of greater than 95 percent.
It has been surprisingly discovered that this composition offers excellent impact, processability and surface aesthetic properties and is ideal for use in extruded sheet applications.
DETAILED DESCRIPTION OF THE INVENTION
The composition of the present invention comprises a hydrogenated block copolymer of alternating blocks having at least three blocks as represented by the formula A(BA)
n
, wherein A is a hydrogenated vinyl aromatic polymer hard block and B is a hydrogenated conjugated diene polymer soft block, wherein n is an integer from 1-3, including triblock, multi-block, tapered block, and star block copolymers, e.g. as SB'S, SB'SB'S, and the like (wherein S is hydrogenated polystyrene, B′ is hydrogenated polybutadiene). The block copolymers may, however, contain any number of additional blocks, wherein these blocks may be attached at any point to the block copolymer backbone, as long as a lamellar morphology is still achieved. Thus, linear blocks would include for example ABA, ABAB, ABABA, ABABAB, and the like. The block copolymer can also be branched, wherein polymer chains are attached at any point along the block copolymer backbone. In addition, blends of any of the aforementioned block copolymers can also be used as well as blends of the block copolymers with their homopolymer counterparts as long as the required properties of the composition are met. In other words, an ABA block copolymer can be blended with a ABABA block copolymer and/or an A homopolymer, as long as lamellar morphology is still achieved.
The vinyl aromatic monomer used in preparing block copolymers, which are subsequently hydrogenated, is typically a monomer of the formula:
wherein R′ is hydrogen or alkyl, Ar is phenyl, halophenyl, alkylphenyl, alkylhalophenyl, naphthyl, pyridinyl, or anthracenyl, wherein any alkyl group contains 1 to 6 carbon atoms which may be mono or multisubstituted with functional groups such as halo, nitro, amino, hydroxy, cyano, carbonyl and carboxyl. More preferably Ar is phenyl or alkyl phenyl with phenyl being most preferred. Typical vinyl aromatic monomers include styrene, alpha-methylstyrene, all isomers of vinyl toluene, especially paravinyltoluene, all isomers of ethyl styrene, propyl styrene, butyl styrene, vinyl biphenyl, vinyl naphthalene, vinyl anthracene and the like, and mixtures thereof. The block copolymer can contain more than one specific polymerized vinyl aromatic monomer. In other words, the block copolymer can contain a polystyrene block and a poly-alpha-methylstyrene block. The hydrogenated vinyl aromatic polymer block may also be a hydrogenated copolymer of a hydrogenated vinyl aromatic, wherein the vinyl aromatic portion is at least 50 weight percent of the copolymer, as long as lamellar morphology is still achieved.
The conjugated diene monomer used in preparing block copolymers, which are subsequently hydrogenated, can be any monomer having two conjugated double bonds. Such monomers include for example 1,3-butadiene, 2-methyl-1,3-butadiene, 2-methyl-1,3 pentadiene, isoprene and similar compounds, and mixtures thereof. In one embodiment, the conjugated diene polymer block is a polybutadiene. Polybutadiene can contain either a 1,2 configuration, which hydrogenates to give the equivalent of a 1-butene repeat unit, or a 1,4-configuration, which hydrogenates to give the equivalent of an ethylene repeat unit.
A block is herein defined as a polymeric segment of a copolymer which exhibits microphase separation from a structurally or compositionally different polymeric segment of the copolymer. Microphase separation occurs due to the incompatibility of the polymeric segments within the block copolymer. The separation of block segments can be detected by the presence of distinct glass transition temperatures. Microphase separation and block copolymers are widely discussed in “Block Copolymers-Designer Soft Materials”, PHYSICS TODAY, February, 1999, pages 32-38.
Block copolymers useful in the composition of the present invention, advantageously have a specific morphology. Morphology is the mesoscopic self assembly of the blocks in the molten and solid states producing compositional patterns as described in “Block Copolymers-Designer Soft Materials”
PHYSICS TODAY,
February 1999 by Bates and Fredrickson. The specific advantageous morphology for use in the composition of the present invention is a lamellar morphology, wherein the self assembly of blocks is in discrete layers. Morphology can be determined by SAXS (small angle x-ray scattering) analysis, which is well known by those skilled in the art and described in
The Physics of Block Copolymers,
Ian W. Hamley, Chapter 5, Oxford University press, 1998, NY.
Lamellar morphology can be achieved in different ways and is dependent upon the phase volume of the soft block segment. Generally, the soft segment phase volume is of a sufficient quantity to achieve a lamellar morphology. Typically the phase volume of the soft block segment will be greater than 35, preferably greater than 37, more preferably greater than 40 and most preferably greater than 45 to 65, preferably to 60, more preferably to 55 and most preferably to 45 weight percent conjugated diene, based on the total weight of the block copolymer. The weight ratio of hydrogenated conjugated diene polymer block to hydrogenated vinyl aromatic polymer block is typically 35:65 or more, preferably greater than 40:60. The total weights of the hydrogenated vinyl aromatic polymer blocks and the hydrogenated conjugated diene polymer block(s) is typically at least 80 weight percent, preferably at least 90, and more preferably at least 95 weight percent of the total weight of the hydrogenated copolymer.
The total number average molecular weight (Mn
t
) of the hydrogenated block copolymers useful in the present invention is typically from 35,000, preferably from 42,000, more preferably from 45,000 and most preferably from 47,000 to 80,000, typically to 70,000, and generally to 60,000. The Mn, as referre
Berglund Charles A.
Hahn Stephen F.
Hahnfeld Jerry L.
Jones Mary Ann
Leibig Cora M.
Dow Global Technology Inc.
Mullis Jeffrey
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