VISCOELASTIC PROPERTIES OF RANDOM POLY(BUTYLENE ADIPATE ISOPHTHALATE)COPOLYMERS/

The viscoelastic properties of random poly(butylene adipate/isophthala te) copolymers of various molecular weights and compositions were inve stigated by dynamic testing in the molten state. For all samples the s torage and loss components of the dynamic shear modulus, G'(omega) and G ''(omega), were measured at different temperatures. The zero-shear viscosity, eta(0), for each composition was correlated to the weight-a verage molecular weight, M(o)mega, by the equation: eta(0)=KM(o)mega(a ) and the exponent a was found to increase as the content of isophthal ate units was increased. Also, increases in the activation energy for viscous flow were observed as the isophthalate unit content was increa sed. The dynamic viscoelastic behavior of the copolymers was studied i n terms of the complex compliances; curve fitting results on data of J '(omega) and J ''(omega) vs. w showed that such curves can be accurate ly reproduced by the following equation: J(omega)=J(g)+(J(e)(0)-J(g)) /[1+(i omega tau(2))(beta 2)]+i/omega eta(0). It was concluded that, i n the investigated frequency and temperature ranges, a single retardat ion phenomenon in the terminal zone provides a satisfactory descriptio n of the viscoelastic behavior of the copolymers. The values of the vi scoelastic parameters were found to vary monotonically with compositio n, as expected in the case of statistical copolymers. (C) 1997 John Wi ley & Sons, Inc.