Viscosity–molecular weight relationship for fractionated poly(ethylene terephthalate)

Poly(ethylene terephthalate) was separated into 12 fractions of equal size by a stepwise increase in the amount of solvent in the two‐phase liquid fractionation system of phenol‐tetrachloroethane (PTCE) (1:1) and n‐heptane. Various molecular weight parameters of the fractions were measured by osmotic pressure and gel‐permeation chromatography. Intrinsic viscosity‐molecular weight plots were made for three different solvents at 25°C. Mark‐Houwink constants for viscosity‐average molecular weight were measured and gave values of K of 2.50, 2.37, and 2.25 × 10−4 dl/g and values of a of 0.73 for 1:1 PTCE, 3:2 PTCE, and o‐chlorophenol, respectively. A comparison with the literature values for this polyester was made, and application of the Mark‐Houwink equation to the determination of number‐average (Mn) and weight‐average (Mw) molecular weight of whole polymers is considered.