The viscoelastic properties of random poly(butylene adipate/isophthalate) copolymers of various molecular weights and compositions were investigated by dynamic testing in the molten state. For all samples the storage and loss components of the dynamic shear modulus, G( v) and GΠ( v), were measured at different temperatures. The zero-shear viscosity, h 0 , for each composition was correlated to the weightaverage molecular weight, M w , by the equation: h 0 Γ
KM a w and the exponent a was found to increase as the content of isophthalate units was increased. Also, increases in the activation energy for viscous flow were observed as the isophthalate unit content was increased. The dynamic viscoelastic behavior of the copolymers was studied in terms of the complex compliances; curve fitting results on data of J( v) and JΠ( v) vs. v showed that such curves can be accurately reproduced by the following equation: J*( v) Γ
J g / (J 0 e 0 J g )/[1 / (ivt 2 ) b 2 ] / i/ vh 0 . It was concluded that, in the investigated frequency and temperature ranges, a single retardation phenomenon in the terminal zone provides a satisfactory description of the viscoelastic behavior of the copolymers. The values of the viscoelastic parameters were found to vary monotonically with composition, as expected in the case of statistical copolymers.