Design of Zero Zero-birefringence Polymers for Injection Molded Products with Low Birefringence

Abstract

Zero zero-birefringence polymers that exhibit no orientational birefringence and no photoelastic birefringence were designed and synthesized based on the analyses of orientational birefringence caused in uniaxially heat-drawn polymer films and photoelastic birefringence caused in elastic deformation of bulk polymers. In this paper, we analyzed birefringence caused in injection molded plates of the polymers in order to evaluate effectiveness of the design method in injection molding. In the case of the ternary copolymer of the zero zero-birefringence polymers, orientational birefringence and photoelastic birefringence were almost zero in the injection molded plates without dependence on the molding temperature. Therefore, we can conclude that effectiveness of the design method has been demonstrated and the ternary polymer is one of ideal zero zero-birefringence polymers. Significantly small birefringence was observed in injection molded plates of zero zero-birefringence polymers containing anisotropic molecule dopants and it was almost eliminated by using a polymer designed by the modified design method. The polymer exhibits small photoelastic birefringence at room temperature because its composition is different from that of the zero zero-birefringence polymer. In the case of the polymer containing anisotropic molecule dopants, design concept, for example elimination of photoelastic birefringence or elimination of birefringence in injection molded samples, is important.