Stock material or miscellaneous articles – Composite – Of bituminous or tarry residue
Patent
1987-10-08
1991-04-16
Lee, John D.
Stock material or miscellaneous articles
Composite
Of bituminous or tarry residue
428394, 525902, G02B 104
Patent
active
050077066
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to optical fibers prepared from polymers. More particularly, it relates to heat resistant, flexible, polymeric optical fibers comprising a core and a cladding.
It is previously known in the art to prepare polymeric optical fibers. For example, see recently issued U.S. Pat. No. 4,505,543 (Ueba et al.). Ueba teaches the use of core polymers of an alkyl methacrylate and certain styrene derivatives. Styrene derivatives such as alpha-methylstyrene and paramethylstyrene are expressly excluded (at column 5, lines 20-25). Ueba also discloses the use of a cladding polymer that is a copolymer of vinylidene fluoride or a perfluoroolefin.
It is previously known that polymeric optical fibers can suitably be prepared only from judiciously selected polymer pairs. A practical polymeric optical fiber must possess simultaneously a number of optimized physical properties. Firstly, the components of polymeric optical fiber must be of a sufficiently high transparency that attenuation of the optical signal over the lengths that optical transmission is desired is not significant. Secondly, the polymer materials of the optical fiber must not be significantly adversely affected at elevated temperatures or other enviromental extremes to which the polymer optical fiber is to be exposed. For example, it is known that many polymer materials demonstrate greatly decreased optical transmission upon exposure to elevated temperatures. For example, the maximum temperature at which poly (methyl methacrylate) and polystyrene can be safely used is about 80.degree. C. At temperatures greater than about 80.degree., such polymers are deformed and their microstructure caused to fluctuate, thereby affecting the optical properties of the fiber even when the fiber is again brought to room temperature.
A third requirement for a suitable polymeric optical fiber is that the polymer used for the cladding must be suitably chosen both in respect to its index of refraction and its ability to bond to the core polymer material. Typically, such core material and cladding material should have refractive indices differing by at least 3 percent. That is, the cladding should be made of a transparent polymeric material having a refractive index of at least 3 percent less than that of the core. It is equally important that the cladding material adhere to the core material such that repeated flexing and bending of the resulting fiber optic does not cause delamination at the interface between the core and cladding material. Such delamination could result in attenuation of the optical signal.
Fourthly, it is desirable in a polymeric optical fiber to employ polymer constituents having low hygroscopicity. Particularly when operating at elevated temperatures, water absorption by certain polymers may lead to unwanted expansion of the polymers as well as adversely affect the polymers optical properties. For example, differing rates of water absorption may lead to differing rates of polymer swelling and contribute to weakening of the adhesive bond between core and cladding. To a certain extent adverse effects caused by hygroscopicity may be reduced by encasing a polymeric optical fibers inside of protective coatings in order to avoid the effects of exposure to high humidity. However, it would be desirable to provide a polymeric optic fiber having reduced hygroscopicity in order that any detrimental effects caused by water absorption may be reduced.
Fifthly, it would be desirable to have a highly flexible filament, such as one that could be tied into a closed knot on itself without breakage of the polymeric optical fiber.
According to the present invention there is now provided a polymer optical fiber having a core and cladding structure characterized by (a) the core essentially comprising a copolymer of at least one monovinylidene aromatic monomer and alpha-methylstyrene prepared by anionically polymerizing the monovinylidene aromatic monomer and from 30 to 70 weight percent of alpha-methylstyrene based on the combined weight of monomer, at a te
REFERENCES:
patent: 4505543 (1985-03-01), Ueba et al.
patent: 4542957 (1985-09-01), Ishiwari et al.
patent: 4564263 (1986-01-01), Ueba et al.
patent: 4681400 (1987-07-01), Ueba et al.
patent: 4693553 (1987-09-01), Sasaki et al.
patent: 4744632 (1988-05-01), Yamamoto et al.
patent: 4756599 (1988-07-01), Maeda et al.
Parker Theodore L.
Perettie Donald J.
Deline Douglas N.
Heartney Phan T.
Lee John D.
The Dow Chemical Company
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