Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Patent
1995-08-10
1997-06-10
Teskin, Fred
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
428394, 428421, 428516, 264 124, 526127, 526132, 526160, 526281, 526308, 526943, 528482, 528491, 528503, 385123, 385141, B32B 2700, C08F 4643, C08F23208
Patent
active
056374003
DESCRIPTION:
BRIEF SUMMARY
The invention relates to thermoplastic cycloolefin copolymers (COCs) having low melt viscosity and low optical attenuation, to a process for their preparation, and to their use as optical waveguides (optical fibers).
Optical waveguides are employed for the transport of light, for example for the purpose of illumination or signal transmission. They generally comprise a cylindrical, light-transmitting core surrounded by a cladding layer of a likewise transparent material with a lower refractive index. Thin-film optical waveguides comprise, for example, three transparent layers, where the two outer layers have a lower refractive index than the central layer. The conduction of light takes place by total reflection at the interface. Transparent materials which can be employed are glasses or (organic or inorganic) polymers.
The most widespread polymer for use as an optical wave-guide, polymethyl methacrylate (PMMA), can only be employed at up to about 85.degree. C. due to its low glass transition temperature of about 106.degree. C. Other known transparent thermoplastics having higher glass transition temperatures, such as, for example, polycarbonate or aromatic polyesters, contain aromatic units in the molecule. These result in increased light absorption in the short-wave spectral region. The use of such polymers for optical waveguides is described in illustrative terms in A. Tanaka et al., SPIE, Vol. 840 (1987).
The heat distortion resistance can be improved by reaction of polymethacrylates. An example which may be mentioned is the polymer-analogous conversion of polymethyl methacrylate into polymethacrylimide. The copolymerization of poly(meth) acrylate with comonomers such as methacrylic anhydride or methacrylonitrile also gives polymers of higher heat resistance than unmodified PMMA. Another route to transparent polymers having increased glass transition temperatures is the use of (meth)acrylates of (per)halogenated or polycyclic aliphatic alcohols or of substituted phenols. The latter likewise have increased light absorption in the shortwave spectral region due to the aromatic units. Although the former compounds give transparent polymers having high glass transition temperatures, conversion, for example, into optical fibers is difficult or impossible due to their inherent brittleness.
All the classes of substances described are hygroscopic due to their polar nature. At elevated temperature, the water content in the polymer can cause undesired degradation reactions during conversion, reducing the practical use value.
However, lower water absorption is exhibited by thermoplastic COCs, which also have increased heat distortion resistance. The complete absence of chromophores, such as double bonds of all types, means that these polymers appear particularly suitable for optical applications. It should also be possible to employ these plastics in the area of light conduction (EP-A 0 355 682 and EP-A 0 485 893).
COCs can be prepared using specific Ziegler catalysts (EP-A 0 355 682), usually using alkylaluminum or alkylaluminum chlorides as cocatalysts. However, these compounds hydrolyze during the work-up process described to give extremely fine, gelatinous compounds which are difficult to filter. If alkylaluminum chlorides are employed, chlorine-containing compounds, such as hydrochloric acid or salts, which are likewise difficult to separate off, are formed during work-up. If hydrochloric acid is employed for the work-up (EP-A 0 355 682 and EP-A 0 485 893), similar problems arise. In particular in the processing of COCs prepared in this way, a brown coloration occurs. In addition, a known problem in the preparation of ethylene-containing cycloolefin copolymers is the formation of partially crystalline ethylene polymers as a byproduct. EP-AU 447 072, for example, describes how cycloolefin copolymers prepared by vanadium catalysis (cf. EP-AO 156 464) can be freed from partially crystalline ethylene polymerization by a complex multistep filtration. The metallocene catalysts described in EP 404 870, with the except
REFERENCES:
patent: 3993834 (1976-11-01), Chimura et al.
patent: 5087677 (1992-02-01), Brekner et al.
patent: 5371158 (1994-12-01), Brekner et al.
Brekner Michael-Joachim
Deckers Hellmuth
Osan Frank
Hoechst Aktiengesellschaft
Teskin Fred
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