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
2000-05-11
2002-09-17
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...
C525S09200D, C525S327800
Reexamination Certificate
active
06451924
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to hydrogenated block copolymers produced from vinyl aromatic and butadiene monomers.
Hydrogenated block copolymers of vinyl aromatic and butadiene monomers such as styrene-butadiene-styrene copolymers are well known in the art and disclosed in U.S. Pat. Nos. 3,333,024; 3,431,323; 3,598,886; 5,352,744; 3,644,588 and EP-505,110. Additionally, U.S. Pat. No. 4,911,966, U.S. Pat. No. 5,178,926 and JP 10-116442 disclose an optical disc substrate made from vinyl cyclohexane copolymers. However, in these applications, the copolymer can be only partially hydrogenated, producing discs having low impact and flexibility properties, low heat distortion temperature, elevated birefringence and otherwise unacceptable properties for commercial disc applications. Birefringence or double refraction is a form of optical distortion determined by the differences in the index of refraction in materials through which light passes. Birefringence affects the phase relationship of laser light, used to read optical media discs resulting in disc reading errors. In current optical media discs, high flow materials such as polycarbonate are used and the discs are molded under conditions which minimizes material stresses. However, the birefringence still approaches levels which can be problematic. The current trend in the optical disc market is directed to higher density discs which will not tolerate the levels of birefringence of the prior art.
Therefore, there remains a need for a transparent polymer and optical media discs made therefrom, having improved impact, flexibility, heat distortion temperature and very low birefringence, or otherwise acceptable properties for high density and commercial disc applications.
SUMMARY OF THE INVENTION
The first aspect of the present invention is directed to hydrogenated block copolymers and optical media discs produced therefrom. The hydrogenated block copolymer is a rigid hydrogenated block copolymer, which comprises at least two distinct blocks of hydrogenated polymerized vinyl aromatic monomer, herein referred to as hydrogenated vinyl aromatic polymer block, and at least one block of hydrogenated polymerized butadiene monomer, herein referred to as hydrogenated butadiene polymer block, wherein the hydrogenated copolymer is characterized by:
a) a weight ratio of hydrogenated butadiene polymer block to hydrogenated vinyl aromatic polymer block of 40:60 or less;
b) a total number average molecular weight (Mn
t
) of from 30,000 to 80,000, wherein each hydrogenated vinyl aromatic polymer block (A) has a Mn
a
of from 10,000 to 50,000 and each hydrogenated butadiene polymer block (B) has a Mn
b
of from 3,000 to 30,000;
c) a hydrogenation level such that each hydrogenated vinyl aromatic polymer block has a hydrogenation level of greater than 90 percent and each hydrogenated butadiene polymer block has a hydrogenation level of greater than 95 percent; and
d) a weight ratio of 1,2 to 1,4 polybutadiene content of greater than 20:80.
Hydrogenated block copolymers having these characteristics are transparent to light at visible wavelengths and are ideally suited for optical disc applications, while possessing excellent properties at both standard and elevated temperatures. The combination of transparency, high glass transition temperature, low water absorption, flexibility, excellent melt processability, and surprisingly negligible birefringence makes these materials ideal candidates for optical disc applications.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hydrogenated block copolymers are prepared by hydrogenating a block copolymer produced from at least one vinyl aromatic monomer and at least one butadiene monomer.
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 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.
The butadiene monomer is 1,3-butadiene. 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. Typically, the weight ratio of 1,2 to 1,4 content of the polybutadiene block is greater than 20:80, generally greater than 25:75, preferably greater than 30:70, and more preferably greater than 35:65. 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.
Rigid hydrogenated block copolymers are defined as having a weight ratio of hydrogenated butadiene polymer block to hydrogenated vinyl aromatic polymer block of 40:60 ore less, typically 35:65 or less, preferably less than 30:70, and more preferably less than 25:75. 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 hydrogenated block copolymers of the present invention are produced by the hydrogenation of block copolymers including triblock, multiblock, tapered block, and star block copolymers such as SBS, SBSBS, and the like (wherein S is polystyrene, B is polybutadiene). The block copolymers contain at least one triblock segment comprised of a vinyl aromatic polymer block on each end, e.g. SBS. The block copolymers may, however, contain any number of additional blocks, wherein these blocks may be attached at any point to the triblock polymer backbone. Thus, linear blocks would include for example SBS, SBSB, SBSBS, SBSBSB, and the like. The copolymer can also be branched, wherein polymer chains are attached at any point along the 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 hydrogenated homopolymer counterparts. In other words, a hydrogenated SBS block copolymer can be blended with a hydrogenated SBSBS block copolymer and/or a hydrogenated polystyrene homopolymer. It should be noted here that in the production of block copolymers, small amounts of residual diblock copolymers can also be produced.
The total number average molecular weight (Mn
t
) of the hydrogenated block copolymers of the present invention is typically from 30,000, preferably from 35,000, more preferably from 45,000 and most preferably from 50,000 to 80,000, typically to 75,000, and generally to 70,000. The Mn, as referred to throughout the present specification, is determined by gel permeation chromatography. The molecular weight of the hydrogenated block copolymer and properties obtained ar
Hahn Stephen F.
Hahnfeld Jerry L.
Jones Mary Ann
Parsons Gary D.
Asinovsky Olga
Dow Global Technologies Inc.
Seidleck James J.
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