Properties of PEO in dilute solution under stirring

The degradation of two high molecular weight PEOs (Mw = 3.3 x 10(4) and 3.3 x 10(6) Da) by stirring using a magnet is studied by static and dynamic light scattering at room temperature in dilute solution in several good solvents. Besides the "parent polymer", three species are formed under stirring: a soluble species having smaller hydrodynamic radius than the original polymer, soluble aggregates of larger dimensions, and insoluble aggregates of several microns. The formation of these species depends on the nature of the solvent and the stirring speed. The low dimension species are generated in allyl alcohol and in methanol/hydroquinone solutions where, in a turbulent flow, the large molecular chains are broken and could form radicals which are deactivated. The formation of the soluble aggregates is the result of the association of several molecules under the effect of orientation in the flow of the monomer units that belong to different molecular chains. These entities are stabilized by dipolar interactions. The subsequent addition of sodium chloride breaks these associations, and well-solvated polymer units are recovered. The insoluble aggregates are preferentially formed in solvents that have intermediate and low values of the dielectric constant (epsilon congruent to 7-40) such as dimethylformamide, acetonitrile, methanol, or methyl acetate. Indeed, in these solvents the formation of living macroradicals in the flow by breaking of the large macromolecular chains could be at the origin of the formation of insoluble reticulated gels.