A new alternating copolymer of stilbene and N-(2-methylphenyl) maleimide) [I] was prepared and exhibited a strong negative birefringence in cast polymer films. The negative birefringence is proposed to result from the sterically crowded backbone which restricts the free rotation of the ortho-methyl phenyl substituent of the enchained maleimide monomer and forces the phenyl ring to exist normal to the plane of the imide ring. Alternating copolymers of styrene with I and stilbene with N-phenylmaleimide did not exhibit similar negative birefringence properties. (C) 2011 Elsevier Ltd. All rights reserved.