Linear viscoelastic properties of partly to completely formylated poly(vinyl alcohols)

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Abstract
Linear viscoelastic behavior of partly to completely formylated poly(vinyl alcohols), including stereoregular poly(vinyl formates), was investigated at various temperatures above the glass-transition temperature to obtain the effect of successive changes of polymer structure from semi- to quasi-crystalline to amorphous upon the mechanical behavior and its temperature dependence. The following two anomalies in the temperature dependence of the mechanical behavior of semi- to quasi-crystalline polymers, in contrast to that of amorphous polymers, were obtained: a deviation in the temperature dependence of the shift factor from the WLF equation used for composing the master relaxation or complex dynamic modulus curve and the appearance of another maximum of apparent activation energy for the relaxation process, both in a range of temperayures corresponding to the leathery plateau of the viscoelastic functions. The above anomalies suggest the existence of another type of inter-molecular relaxation mechanism at the leathery plateau for the partly formylated polymers, which is probably due to a loosening of the crystal structure in contrast to merely mechanical entanglement between polymer chains for amorphous polymers. From the complex modulus function, two types of relaxation mechanisms, intra- and intermolecular relaxation mechanisms, were separated for the partly formylated polymers on the basis of a few reasonable assumptions from the phenomenological viewpoint of linear viscoelasticity.