Study of the dynamic interactions of macromolecules in concentrated polymer solutions using spin labelling

Abstract

The intermolecular spin exchange rate constants and the rotational diffusion correlation times have been measured for spin labels (side groups of poly(glycidyl methacrylate)) in concentrated polymer solutions ( c p ⩽ 0.50 g/ml). The spin exchange was measured with average spacings of ∼30Å between the labels. It is shown that the rate of translational and rotational mobility of the labels at c p ⩽ 0.25 g/ml decreases in thermodynamically “good” solvents by a factor of ∼1.6 as the polymer concentration rises. On this basis it is proposed that in concentrated polymer solutions the “freely permeating coils” model (average degree of polymerization of the polymer P=690 ) should hold up to c p=0.25 g/ml. An analysis of the results obtained and of data in the literature leads to the tentative proposal of a threshold polymer concentration in thermodynamically “good” solvents at which solutions may become “insensitive” to their quality (at the iso point).