Abstract
A study was made of the viscoelastic properties, glass temperature and stress-strain properties of the PVA-PVAc block and graft copolymers and to determine the manner in which the PVAc domains influence the viscoelastic and ultimate tensile properties. The results obtained were as follows.
a) The modulus of the block copolymers with the high degree of acetylation of heattreated PVA films, was represented by the simple series mechanical model, that is, the complex elastic modulus E of this system was described by the equation of E= [φ/EA+ (1-φ) /EB] -1, where φ is the volume fraction of PVAc.
EA and EB are the complex elastic moduli of PVAc and PVA, respectively.
b) The modulus of the recasted block copolymers with the low degree of acetylation of heat-treated PVA films was also represented by the same series mechanical model, but in case of the high degree of acetylation, the phase seperation of PVA and PVAc decreased.
c) The temperature of the maximum E″ of block and random copolymers did not change by the degree of acetylation, but in the case of the graft copolymers, the temperature of the maximum E″ was shifted to the higher temperature side. The causes of this phenomena were supposed to depend on the crosslinking of PVA by PVAc.
d) The yield strength of the PVA-PVAc block copolymers decreased with the increasing degree of acetylation, but the elongation showed the maximum values at the degree of acetylation about 20-30%. The yield strength of the PVA-PVAc graft copolymers did not change with the rising degree of grafting, but the elongation decreased rapidly with the increasing degree of grafting.
