Radiation curable compositions with multi-functional long-armed oligomers for coating optical fibers

A radiation curable composition for use as an optical fiber primary coating comprising, consisting of, or consisting essentially of:

• an oligomer component;
• a diluent component;
• a photoinitiator component;
• and
• optionally, an additive component;
• wherein the oligomer component comprises, consists essentially of, or consists of a reactive urethane oligomer having at least three arms each having a most distal termination point and bound together at a single junction point, wherein at least one arm comprises the reaction product of
• a polyol;
• a polyisocyanate;
• and
• an isocyanate-reactive (meth)acrylate;
• wherein the reactive urethane oligomer possesses a number average molecular weight (Mn) and a Z-average molecular weight (Mz),
• wherein the Mn is greater than or equal to about 10 kilodaltons (kDa);
• and
• Mz/Mn is greater than or equal to 4.5, or from 4.5 to 15, or from 4.5 to 10, or from 4.5 to 8, or from 4.5 to 6;
• wherein Mn and Mz are measured by a size exclusion chromatography (SEC) method.