STRUCTURE-DEPENDENT MAGNETIC-SUSCEPTIBILITY OF SHARP POLY(ETHYLENE OXIDE) FRACTIONS

Nine sharp fractions of poly(ethylene oxide) (PEO) glycol with number- average molar masses [M-n] in the range from 0.6 x 10(3) to 20 x 10(3) (PEO-0.6 to PEO-20) were characterized by magnetic susceptibility chi measured in the temperature interval 293 K to 378 K. In contrast to t he liquidlike PEG-0.6 with temperature-invariant chi, the values of ch i for each of the remaining solid samples, after the initial increase, exhibited two plateaus separated by a relatively narrow temperature i nterval of their second increase. The jumps of chi at lower and higher temperatures were attributed to a solid-state transition of-unspecifi c nature and to the melting of the crystal fraction, respectively. The temperature-invariant values of chi(n) in the melt state above T-m pa ss through a minimum for the sample PEG-2.0 and then increase again wi th [M-n] to a limiting value chi(infinity) = -0.622 x 10(-6). It is co ncluded that a considerable contribution of the molar-mass-dependent ' 'paramagnetism'' chi(p) = chi - chi(d) (where chi(d) is the diamagneti c contribution estimated by Kirkwood's equation) to the total magnetic susceptibility of PEO fractions reflects distortions of the spherical symmetry of the electron shells around chain atoms resulting from the discontinuous change of both inter- and intrachain interactions as th e [M-n] increases through and above the critical crossover molar mass [M-cr] = 2 x 10(3).