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
2001-10-31
2003-06-24
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...
C525S332900, C428S064400, C428S065100
Reexamination Certificate
active
06583230
ABSTRACT:
BACKGROUND
The present invention relates to hydrogenated block copolymers. In particular, the invention relates to hydrogenated block copolymers prepared from vinyl aromatic and conjugated diene monomers.
Copending applications Ser. No. 09/695,041, filed Oct. 24, 2000, disclose pentablock and other multi-block hydrogenated copolymers. However, these polymers typically have the structure ABABA, wherein A is a hydrogenated vinyl aromatic polymer block, B is a hydrogenated conjugated diene block and the copolymer is symmetrical in molecular weights, that is all A blocks have the same molecular weight and all B blocks have the same molecular weight.
Fully hydrogenated block copolymers prepared from vinyl aromatic and conjugated diene monomers, wherein both blocks are substantially saturated, are well known in the art. U.S. Pat. No. 3,333,024 and U.S. Pat. No. 3,431,323 disclose hydrogenated triblock (ABA) copolymers of vinyl aromatic and conjugated diene polymers having a 20 to 30 percent hydrogenation level and improved tensile properties, when compared to their non-hydrogenated counterparts. However, such copolymers containing very low molecular weight hydrogenated polystyrene blocks, for example 4,000, have low heat resistance and do not afford rigid compositions with good physical properties. U.S. Pat. No. 3,598,886 discloses hydrogenated vinyl substituted aromatic hydrocarbon-conjugated diene block copolymers having less than 3 percent aromatic unsaturation, however the compositions disclosed do not have a good balance of physical properties and processability. Moreover,
Thermoplastic Elastomers
, Chapter 14, Ed. N. R. Legge, et al., Hanser Publishers, New York, 1987 discloses that fully hydrogenated block copolymers have generally poor physical properties at only slightly elevated temperatures.
U.S. Pat. No. 4,911,966 issued to Mitsubishi discloses hydrogenated vinyl aromatic polymers and copolymers and their use in optical media applications. However, the broad composition disclosed suffer from numerous disadvantages including high birefringence, poor processability and poor dimensional stability in such applications.
Therefore, it remains desirable to obtain a hydrogenated block copolymer composition prepared from a vinyl aromatic and a conjugated diene monomer having improved physical properties, retention of these properties at elevated temperatures, and good birefringence, processability and dimensional stability for use in thin wall injection molding applications.
SUMMARY OF THE INVENTION
The present invention is a composition comprising an alternating hydrogenated block copolymer having at least two blocks of hydrogenated vinyl aromatic polymer and at least one conjugated diene polymer block, wherein the number average molecular weights (Mn) of each block can be different.
In one aspect, the present invention is a composition comprising a hydrogenated pentablock copolymer prepared by hydrogenating a pentablock copolymer produced from at least one vinyl aromatic monomer and at least one conjugated diene monomer, wherein the hydrogenated pentablock copolymer has a total number average molecular weight (Mn
t
) of from 40,000 to 70,000 and is of the structure ABA′B′A″, and wherein each vinyl aromatic polymer block, herein referred to as A type block (A, A′, A″) has a Mn
a
of from 8,700 to 21,000 and is hydrogenated to greater than 90 percent, and each conjugated diene polymer block, herein referred to as B type block (B, B′) has a Mn
b
of from 2,000 to 12,500, further characterized in that the total amount of type B block (B, B′) is from 10 to 35 weight percent of the copolymer based on the combined weights of all blocks, and are hydrogenated to greater than 95 percent, while A type blocks (A, A′, A″) are hydrogenated to at least 90 percent. Additionally, the number average molecular weights (Mn) of the A type blocks are such that at least one A type block varies significantly in Mn from the other A type block(s).
The hydrogenated copolymers of the present invention having these Mn, block content and hydrogenation characteristics, have superior properties and processability characteristics when compared to other block and pentablock copolymers, especially in thin wall injection molding applications such as optical media discs. The hydrogenated copolymers of the present invention also exhibit higher resistance to yield, and improved toughness.
The hydrogenated copolymers of the present invention are advantageously used in thin wall injection molded applications such as optical media discs due to their excellent processability, birefringence, dimensional stability and other physical properties.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a composition comprising an alternating hydrogenated pentablock copolymer, wherein the copolymer is prepared by hydrogenating a pentablock copolymer produced from at least one vinyl aromatic monomer and at least one conjugated diene monomer, having the structure ABA′B′A″, wherein the A type block is a hydrogenated polymerized vinyl aromatic monomer, herein referred to as hydrogenated vinyl aromatic polymer, and the B type block is a hydrogenated polymerized conjugated diene monomer, herein referred to as a hydrogenated conjugated diene polymer.
The vinyl aromatic monomer 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 pentablock copolymer can contain more than one specific polymerized vinyl aromatic monomer. For instance, the pentablock copolymer can contain a polystyrene block and a poly-alpha-methylstyrene block. The hydrogenated vinyl aromatic polymer block may also be a copolymer of a vinyl aromatic wherein the vinyl aromatic portion is at least 50 weight percent of the copolymer.
The conjugated diene monomer can be any monomer having 2 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. The pentablock copolymer can contain more than one specific polymerized conjugated diene monomer. In other words, the pentablock copolymer can contain a polybutadiene block and a polyisoprene block.
The conjugated diene polymer block can be chosen from materials which remain amorphous after the hydrogenation process, or materials which are capable of crystallization after hydrogenation. Hydrogenated polyisoprene blocks remain amorphous, while hydrogenated polybutadiene blocks can be either amorphous or crystallizable depending upon their structure. 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. Polybutadiene blocks having at least approximately 40 weight percent 1,2-butadiene content, based on the weight of the polybutadiene block, provides substantially amorphous blocks with low glass transition temperatures upon hydrogenation. Polybutadiene blocks having less than approximately 40 weight percent 1,2-butadiene content, based on the weight of the polybutadiene block, provide crystalline blocks upon hydrogenation. Depending on the final application of the polymer it may be desirable to incorporate a crystalline block (to improve solvent resistance) or an amorphous, more compliant block. The conjugated diene polymer
Fredrickson Glenn H.
Hahn Stephen F.
Leibig Cora M.
Reinhardt Molly T.
Asinovsky Olga
Seidleck James J.
The Dow Chemical Company
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