Miscibility Control of Polystyrene and 4-Pentyl-4'-Cyanobiphenyl by Partial p-Hydroxymethylation
Shogo NOBUKAWA, Osamu URAKAWA, Toshiyuki SHIKATA, and Tadashi INOUE
Abstract:We investigated the effect of hydrogen-bonding on the miscibility of partially p-hydroxymethylated polystyrene (PSOH) and 4-pentyl-4'-cyanobiphenyl (5CB) blends by means of polarized-optical microscopy and infrared (IR) spectroscopy. The blend of polystyrene (PS, the weight average molecular weight Mw is 15.9×103) and 5CB underwent phase-separation into nematic (N) and isotropic (I) phases by decreasing the temperature. We evaluated the N-I transition temperature TNI of all the blends, and examined the effect of the OH content in the PSOH on the TNI values. In the case of the OH content of 5mol% (denoted as PSOH5), the observed TNI of the PSOH5/5CB blend was lower than that of PS/5CB blend, compared at the same blend composition. We concluded that this was caused by the intermolecular hydrogen-bonding between CN group of 5CB and OH groups of PSOH, which was confirmed by the IR spectroscopy. However, as the increase of the OH content, the TNI’s increased, meaning the decrease of the miscibility. Especially, the PSOH25/5CB blend showed higher TNI than that of PS/5CB blend. From the IR spectrum of this blend, the formation of the hydrogen-bonds between the OH groups (self-association) was found to become dominant. Therefore it was suggested that the hydrogen-bonds between the same species resulted in the lower miscibility of the blends. Key Words:Hydrogen-bond, Miscibility, Liquid crystal, Polystyrene, Phase separation, Nematic phase