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
2000-05-31
2002-04-23
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S332900, C525S338000, C525S339000, C428S064400, C358S473000
Reexamination Certificate
active
06376621
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to hydrogenated block copolymers produced from vinyl aromatic and isoprene 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. Nos. 4,911,966, 5,178,926 and JP 10-116442 disclose an optical disc substrate made from vinyl cyclohexane copolymers. However, hydrogenated copolymers derived from butadiene containing copolymers are often unacceptable in optical applications due to elevated form birefringence. 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. Form birefringence is well known and discussed by R. Pix and R. Schirrer in Colloid and Polymer Science, 259, 435-46 (1981) and explained in O. Weiner's classical theory (Weiner, O., Abh. Sachs. Ges. Wiss., Math-Phys. KI. 32m 509 (1912) and Born, M., E. wolf, Principles of Optics, 5
th
ed., 705 (1975)). Birefringence affects the phase relationship of laser light used to read optical media discs and results 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 isoprene monomer, herein referred to as hydrogenated isoprene polymer block, wherein the hydrogenated copolymer is further characterized by:
a) a weight ratio of hydrogenated isoprene 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 150,000, wherein each hydrogenated vinyl aromatic polymer block (A) has a Mn
a
of from 6,000 to 60,000;
c) a hydrogenation level such that each hydrogenated vinyl aromatic polymer block has a hydrogenation level of greater than 90 percent and each hydrogenated isoprene polymer block has a hydrogenation level of greater than 95 percent.
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 a vinyl aromatic monomer and a isoprene 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 copolymer of a vinyl aromatic, wherein the hydrogenated vinyl aromatic portion is at least 50 weight percent of the copolymer.
The hydrogenated block copolymer of the present invention comprises at least one hydrogenated polymerized isoprene monomer. The hydrogenated polyisoprene block may also be a hydrogenated copolymer of isoprene and a conjugated diene, such as butadiene, wherein the hydrogenated polyisoprene portion is at least 50 weight percent of the hydrogenated copolymer, preferably at least 60, more preferably at least 70 and most preferably at least 80 weight percent.
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.
The hydrogenated block copolymers of the present invention typically has a weight ratio of hydrogenated isoprene polymer block to hydrogenated vinyl aromatic polymer block of 40:60 to 5:95, preferably from 35:65 to 10:90, more preferably from 30:70 to 15:85, based on the total weight of the hydrogenated isoprene polymer block and the hydrogenated vinyl aromatic polymer block. The total weights of the hydrogenated vinyl aromatic polymer blocks and the hydrogenated isoprene 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 SIS, SISIS, and the like (wherein S is polystyrene, I is polyisoprene). The block copolymers contain at least one triblock segment comprised of a vinyl aromatic polymer block on each end of the segment. 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 SIS, SISI, SISIS, SISISI, 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 SIS block copolymer can be blended with a hydrogenated SISIS 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 24,000, preferably from 30,000, more preferably from 40,000 and most preferably from 50,000 to 150,000, typically to 135,000, generally to 100,000, preferably to 90,000, more preferably to 80,000, and most preferably to 75,000. The Mn is determ
Hahn Stephen F.
Hahnfeld Jerry L.
Lipman Bernard
The Dow Chemical Company
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