New concept of reducing a birefringence of poly(ethylene naphthalate) by a novel alloy with fluorene‐based polyester

This study proposes the new concept of reducing the birefringence of poly(ethylene naphthalate) (PEN) by a novel alloy with fluorene-based polyester (FBP) involving the “cardo” structure in it. The alloys composed of PEN and FBP were prepared by simple melt blending method (process A) and reactive melt blending (process B). The resulting alloys were characterized by DSC, XRD, DMA, tensile testing, and polarized light microscopy. All PEN-FBP alloys showed transparency and a single glass transition temperature (Tg), indicating that PEN-FBP alloys were completely compatible. It was also demonstrated that Tg for PEN was shifted to the high-temperature side by alloying with FBP. A large amount of the orientation-induced birefringence was induced in drawn PEN sheets; however, in the cases of PEN-FBP alloys, it was drastically decreased because of alloying with FBP. We could reveal the new concept for “low-orientation-induced birefringence material.” POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers