Plastic optical fibers

Claim 1

A core-clad plastic optical fiber comprising (a) a polyglutarimide series polymer having a polymeric structural unit represented by formula (I) ##STR5## wherein R represents a hydrogen atom, an alkyl group, a cycloalkyl group, or an aromatic group and n represents a positive integer, having a thermal deformation temperature of at least 120° C. as a core, and (b) an organic polymer having a refractive index lower than the refractive index of the core as a cladding layer, said plastic optical fiber having the characteristic that the light transmission loss measured at 655 nm is not more than 500 dB/km, wherein the polyglutarimide series polymer forming the core is a polymer produced by solution polymerization using an aromatic hydrocarbon solvent selected from benzene, toluene, ethylbenzene and xylene under the polymerization temperature of 60° C. to 140° C. and has a YI S value of not more than 3 in a mixed solvent of said aromatic hydrocarbon and methanol, reacting polymethyl methacrylate polymer solution with an amine represented by formula (II) R'--NH.sub.2 (II) wherein R' represents a hydrogen atom, an alkyl group, a cycloalkyl group, or an aromatic group, and then removing volatile components in the reaction system, wherein said polymethyl methacrylic polymer contains not more than 500 ppm of impurities, measured by gas chromatography, which react with the amine shown by formula (II) to form yellow materials.