Orientational behavior and mechanical properties of high-molecular-mass poly(vinyl alcohol)

Changes in molecular orientation during the uniaxial thermal drawing of hig h-molecular-mass poly(vinyl alcohol) were studied by the methods of birefri ngence, isometric heating, and IR dichroism. The orientational behavior of this polymer may be divided into two stages related to different mechanisms of rearrangement of molecular structure under thermal drawing. According t o the birefringence data, at the first stage of tensile drawing (below lamb da = 4), the degree of orientation is almost independent of the polymer mol ecular mass and is provided by the chain orientation in amorphous phase. As the molecular mass of the polymer is increased, in the region of high draw ratios, the degree of orientation dramatically increases, and the mechanic al characteristics are substantially improved. As a rule, highly oriented f ilms of high-molecular-mass poly(vinyl alcohol) are characterized by high s trength (1.6-2.4 GPa) and elastic modulus (40-55 GPa).