Design and synthesis of zero-zero-birefringence polymers using N-methylmaleimide

Zero-zero-birefringence polymers which exhibit no orientational birefringence and no photoelastic birefringence may be suitable candidates for the components of optical devices. To develop zero-zero-birefringence polymers, a novel copolymerization system is required. We investigated two types of birefringence of poly(N-methylmaleimide) (PMeMI) and showed that PMeMI exhibits positive orientational and photoelastic birefringence. On the basis of the results, we calculated the optimal composition for compensating both types of birefringence by solving three equations which describe the relationship between birefringence properties and weight fraction of monomers. When the copolymer compositions were MMA/BzMA/MeMI = 86/8/6 and 88/8/4 (wt %), zero-zero- birefringence polymers were obtained. By using MeMI as a comonomer, these zero-zero-birefringence polymers have a much higher glass transition temperature (T_g) than those of previous researches. Also, this polymer film has high transparency comparable with that of PMMA film. Therefore, we conclude that we successfully prepared zero-zero-birefringence polymers using N-substituted maleimide and that N-substituted maleimide is a promising material for zero-zero-birefringence polymers for optical devices.