Intrinsic viscosity–molecular weight relationship for low molecular weight nylon 6

Samples of nylon 6 have been prepared by the hexamethylene diamine-initiated polymerization of ?-caprolactam at 220°C. Fractionation of these with m-cresol–diethyl ether at 26°C yielded 15 amino-terminated fractions of M?_n of 337–10,940 determined conductometrically. Below M?_n = 4,306 the Mark-Houwink parameters in m-cresol at 30°C are K = 3.0 × 10^?3 dl/g and v = 0.53 ± 0.02. Thereafter v exhibits a pronounced increase. The value of K is similar to the values of Kθ derived from Stockmayer-Fixman plots of published data in good solvents. The findings thus corroborate a current hypothesis that fractionated, low molecular weight polymers in good solvents tend to behave viscometrically, as if they were under θ conditions (i.e., K = K_θ and v = 0.50).