ABSTRACT Orientation studies of miscible amorphous hydrogen bond forming blends are reviewed and compared with blends presenting either weaker (van der Waals, electrostatic, etc.) or stronger ionic interactions. Current knowledge and proposed theories on initial deformation and subsequent relaxation, which both contribute to final measured orientation, are briefly reviewed. As the main measurement technique for blends remains FTIR spectroscopy, problems related to determination of the α angle (angle between the vibration vector and the chain axis), which is essential for determining absolute orientation factors P2, are discussed. The choice of a reference temperature and its implications is also mentioned. The two factors most invoked to explain qualitatively orientation behaviour of polymer blends, namely the chain friction coefficient, ξ, and the molecular mass between entanglements, Me, are reviewed in more details. Systems showing a maximum in the orientation function are specifically discussed. It is concluded that orientation of hydrogen bond forming polymers does not differ significantly from that of other blends. The effect of hydrogen bonds in studied systems includes hindering of relaxation and possible cooperativity of deformation or relaxation mechanisms. Future perspective in orientation measurements include molecular modelling and faster measurement methods, such as the polarization modulation infrared linear dichroism technique.
Buy this Article
|