Plastic optical fibers or plastic optical fiber cores with good high temperature resistance to optical attenuation loss are prepared from a cyclic block copolymer characterized by a: A. Weight ratio of hydrogenated conjugated diene polymer block to hydrogenated vinyl aromatic polymer block of 35:65 to 10:90; B. Number average molecular weight (Mn) of from 40,000 to 150,000, grams per mole (g/mol); and C. Hydrogenation level such that each hydrogenated vinyl aromatic polymer block and each hydrogenated conjugated diene polymer block has a hydrogenation level of at least 95 percent.