Poly(sec-butyl crotonate) (poly(SBC)) was prepared by anionic polymerization. 1,1-Diphenylhexyllithium was found to be an effective initiator. Poly(SBC) showed the same optical properties as poly(methyl methacrylate) (poly(MMA)) but different features : poly(SBC) had a high glass transition temperature (T-g) and very high extensibility below T-g, in comparison to poly(MMA). Poly(SBC) can be expected to find applications as an optical material having high flexibility and high service temperature.