Process for producing hydrogenated...

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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C525S332100, C525S338000, C525S339000

Reexamination Certificate

active

06232407

ABSTRACT:

DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a process for producing a hydrogenated &agr;-olefin-dicyclopentadiene copolymer, a method for molding the same and an optical material obtained from the same.
Alpha-olefin-cyclic olefin copolymers obtained by the addition-copolymerization of an &agr;-olefin and a cyclic olefin are synthetic resins having excellent transparency, heat resistance, weatherability, chemical resistance, solvent resistance, dielectric characteristics and various mechanical properties and are widely used in various fields.
These &agr;-olefin-cyclic olefin copolymers are generally produced by the addition-copolymerization of an &agr;-olefin and a cyclic olefin in ahydrocarbon-based solvent such as toluene, cyclohexane or hexane in the presence of an addition polymerization catalyst.
When a copolymer of an &agr;-olefin and a cyclic olefin having at least two double bonds between carbons, namely, a cyclic polyene, is used as a resin, the double bonds between carbons contained in the copolymer must be saturated by hydrogenation to improve heat resistance, weatherability and light resistance. The hydrogenation of a polymer is generally carried out through a reaction between a copolymer and hydrogen in the presence of a heterogeneous or homogeneous hydrogenation catalyst.
The inventors of the present invention have found that, among &agr;-olefin-cyclic polyene copolymers, an &agr;-olefin-dicyclopentadiene copolymer, which is obtained when dicyclopentadiene is used as a cyclic polyene, does not contain the linkages of the dicyclopentadiene and has high chemical homogeneity and that a hydrogenated &agr;-olefin-dicyclopentadiene copolymer is particularly excellent in optical homogeneity and transparency and suitable for use as an optical material for an optical disk substrate or the like and have previously proposed the copolymer (WO98/33830).
The hydrogenated &agr;-olefin-dicyclopentadiene copolymer is generally produced through the step of polymerizing an &agr;-olefin and dicyclopentadiene in a hydrocarbon solvent, the step of hydrogenating the obtained &agr;-olefin-dicyclopentadiene copolymer, the step of removing the catalyst and the step of removing volatile components.
In the polymerization reaction step, in order to obtain a copolymer having high chemical homogeneity, it is extremely important to maintain the ratio of the &agr;-olefin to the dicyclopentadiene at a value higher than a predetermined value. As a result, unreacted dicyclopentadiene inevitably remains in a solution after polymerization. In the subsequent hydrogenation reaction step, the residual dicyclopentadiene is hydrogenated together with the copolymer to be converted into tetrahydrodicyclopentadiene and eventually separated from the hydrogenated copolymer together with the solvent in the step of removing volatile components.
The ignition point of the by-produced tetrahydrodicyclopentadiene is 235° C., which is much lower than that of a commonly used solvent (toluene: 480° C., cyclohexane: 260° C.). Therefore, it is not preferred from the viewpoint of preventing a danger to keep a polymer solution containing tetrahydrodicyclopentadiene at a temperature higher than 235° C. in ordinary equipment, even if it is in an inert atmosphere. This problem can be solved by using perfect airtight equipment but a great load is imposed on equipment in an industrial-scale production. Therefore, it is very difficult to produce the hydrogenated &agr;-olefin-dicyclopentadiene copolymer on an industrial scale.
JP-A 64-54011, JP-A 5-17527 and JP-A 8-239415 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) disclose solvents used for a copolymerization reaction between an &agr;-olefin and dicyclopentadiene and JP-A 63-243103 discloses a solvent used for the hydrogenation reaction of an ethylene-dicyclopentadiene copolymer. Most of the solvents are compounds having a boiling point lower than the boiling point of tetrahydrodicyclopentadiene (194° C. at 760 mmHg). When a solvent having such a low boiling point is used, the solvent is first distilled off in the step of removing volatile components and then tetrahydrodicyclopentadiene is distilled off. However, when the solvent is almost completely distilled off, the hydrogenated copolymer becomes solid at a temperature lower than the ignition point of tetrahydrodicyclopentadiene, thereby making it extremely difficult to completely distill off tetrahydrodicyclopentadiene. Some solvents having a boiling point higher than that of tetrahydrodicyclopentadiene are also enumerated. All of them, however, have a high melting point and are not suitable for use in a polymerization reaction or have a low ignition point of around 250° C. or low solubility for polymers. Therefore, they cannot be used in actual production.
As described above, tetrahydrodicyclopentadiene cannot be removed from the copolymer solution safely and efficiently by conventionally known methods.
When a commonly used hydrocarbon-based solvent such as toluene or cyclohexane is used, there arises another serious problem to be solved in the step of removing volatile components. Since the boiling point of the hydrocarbon-based solvent is lower than the melting temperature of the polymer by 100° C. or more, the polymer becomes solid when the solvent is completely distilled off, thereby making stirring extremely difficult. It is possible to obtain a molten polymer without passing through a solid state by carrying out the operation of removing volatile components in a pressurization system and increasing the boiling point of the solvent. However, the control of a reaction is extremely difficult and a great load is imposed on equipment. Thus, there has been no method for directly converting the polymer from a solution state into a molten state with ease, and the development of this method has been desired.
On the other hand, not only transparency but also various characteristic properties such as optical isotropy (low birefringence), dimensional stability, weatherability and thermal stability are required for plastics used as an optical material for optical disk substrates and optical lenses and the like. For these optical applications, polycarbonates and poly(methyl methacrylate) have been mainly used. However, molded products of polycarbonates are liable to show optical anisotropy due to large specific birefringence, whereas poly(methyl methacrylate) are inferior in dimensional stability due to extremely high water absorption and have low heat resistance. Although polycarbonates are mainly used for optical disk substrates nowadays, there arise concerns about such problems as the large birefringence of the polycarbonates and the warp of a disk by moisture absorption, along with a recent attempt to increase the capacity of a magneto-optical recording disk (MOD) or to increase the recording density as typified by the development of a digital video disk (DVD).
In view of the above situation, the development of cyclic olefin polymers as substitutes for polycarbonates is now under way intensively. These cyclic olefin-based resins are expected to be used as thermoplastic transparent resins having small birefringence and high heat resistance for an optical material for optical lenses and optical sheets in addition to optical disk substrates.
It is an object of the present invention to provide a process for producing a hydrogenated &agr;-olefin-dicyclopentadiene copolymer.
It is another object of the present invention to provide a process for producing a hydrogenated &agr;-olefin-dicyclopentadiene copolymer, which is capable of removing unreacted dicyclopentadiene or tetrahydrodicyclopentadiene, which is the hydrogenated product of dicyclopentadiene, safely and efficiently.
It is still another object of the present invention to provide a method for melt molding of a hydrogenated &agr;-olefin-dicyclopentadiene copolymer.
It is a further object of the present invention to provide a method for melt molding of a hydrogenated &agr;-olefin-dicyclopentadiene copol

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