Preparation of a zero-birefringence polymer doped with a birefringent crystal and analysis of its characteristics

We proposed the "birefringent crystal dopant method" in order to compensate the birefringence of polymers. In this method, the birefringence was compensated by homogeneous doping with a needlelike crystal which has the opposite birefringence to that of the polymers. Strontium carbonate (SrCO ₃) was selected for this purpose because it has a large birefringence and a needlelike shape. SrCO₃ was synthesized, with a length of about 200 nm and a width of about 20 nm, and doped into a poly-(MMA/BzMA=78/ 22(w/w)) film. The film was drawn at 130°C and 4 mm/min. The orientational birefringence of the drawn polymer film at a wavelength of 633 nm was compensated by doping with 0.3 wt % SrCO₃ without losing its transparency and thermostability. The analysis of infrared dichroism of the films showed that the birefringence of the films was compensated at a low concentration of SrCO₃ because of its orientation-inhibition effect and its high orientation degree as compared with that of the polymer main chains.