Strong orientation correlation and optical anisotropy in blend of cellulose ester and poly(ethylene 2,6‐naphthalate) oligomer

Molecular orientation of two aromatic additives in cellulose acetate propionate (CAP) matrix was investigated from orientation birefringence data and an intermolecular orientation correlation represented by nematic interaction (NI) was evaluated. Poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) oligomers with low molecular weight (ca. 400 g mol^?1) were used as the additives. The NI strengths of CAP‐PET and CAP‐PEN were determined to be 0.28 ± 0.05 and 0.96 ± 0.15, respectively. In particular, compared with other polymer/polymer and polymer/small additive blends, the NI value in CAP/PEN blend is much stronger and represents the perfect orientation correlation. The strong orientation correlation is possibly due to the rigid naphtalate structure in PEN. Contrary, a relation between birefringence and orientation function for CAP in bulk and blend showed the same trend, suggesting that the orientation behavior of CAP determines the orientation birefringence. As two ester groups in CAP are responsible for birefringence, the alignment of the ester groups is affected by only the main chain orientation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40570.