The effect of flexible chains on the orientation dynamics of small molecules dispersed in polymer films during stretching

Abstract

The effect of flexible chains on the orientation dynamics of small additive molecules in cellulose acetate propionate (CAP) films is investigated during stretching using birefringence and polarized Fourier-transform infrared (FT-IR) spectra measurements. The orientation birefringence is enhanced by additives such as ethylene 2,6-naphthalate (C2Np) and hexamethylene 2,6-naphthalate (C6Np) oligomers, suggesting that the additives orient parallel to the CAP chain as a result of an intermolecular orientation correlation referred to as the nematic interaction (NI). At a high drawing temperature, the orientation of C2Np is stronger than that of C6Np, indicating that the flexible alkyl chain has reduced the intermolecular NI with CAP. By contrast, C6Np orients along the stretching direction at low temperatures. Polarized FT-IR spectra show that the orientation of the rigid portions of C6Np is delayed relative to those of the flexible groups and the matrix CAP chain. Consequently, the contribution of C6Np to birefringence and its wavelength dependence become stronger as the draw ratios increase. Orientation dynamics of small additive molecules in polymeric films during hot-stretching was investigated by using birefringence analysis and polarized Fourier-transfer infrared (FT-IR) spectroscopy. Birefringence data indicated parallel orientation of the small molecules to main chain of the matrix polymer. Furthermore, polarized FT-IR spectra demonstrated that the ratio of orientation functions of rigid and flexible portions in hexa-methylene naphthalate oligomer showed temperature dependence. The result suggests that the small molecules exhibit two-step orientation in the matrix polymer during stretching.