Zero-birefringence polymers for optical devices

Optical polymers which exhibit no birefringence with any orientation of polymer chains are desirable to realize high performance optical devices that handle polarized light. We defined such polymers as "zero-birefringence polymer" and demonstrated two methods for synthesizing the zero-birefringence polymers: the random copolymerization method and the anisotropic molecule dopant method. Orientational birefringence is compensated by random copolymerization using a positive and a negative birefringence monomers at specified ratio in the random copolymerization method. Poly(methyl methacrylate-co-benzyl mehtaylate) (methyl methacrylate / benzyl methacrylate = 82/18 (wt./wt.)) synthesized by this method showed no orientational birefringence with any orientation degree. In the anisotropic molecule dopant method, orientational birefringence of polymers is compensated by doping anisotropic molecules having opposite anisotropy of polarizability compared to host polymers. Orientational birefringence of poly(methyl methacrylate) was completely compensated by doping with 3 wt% of trans-stilbene as the anisotropic molecule. Furthermore, we demonstrated the isotropic particle dopant method to reduce orientational birefringence of polymers. Orientational birefringence for polymethyl methacrylate film was decreased by approximately 20 % by doping with 2 wt% of silica particles with an average diameter of 7 nm as the isotropic particle dopant.