An investigation has been made into the variability and interconnections of three constants-a viscosity coefficient 70, a stress relaxation time A1 and a rate of strain relaxation time A2-which serve to characterize the behaviour of a dilute solution of highly polymerized methyl methacrylate in a simple shearing motion at small rates of strain. The principal experimental results, which refer to solutions containing between 1 and 10 % of polymer in toluene, pyridine, cyclohexanone and n-butyl acetate, were derived from observations with a coaxial-cylinder elastoviscometer at temperatures in the range 15" to 45" C . No large deviations of A2 from the value 0.015 sec were observed, but both 90 and A1 varied with polymer concentration, the nature of the solvent, and temperature ; values of A1 between 0.02 and 0.2 sec were found, and these corresponded with values of 70 between 1 and 20 poises. It is deduced that, under the experimental conditions, relaxation of shear stress and of rate of strain were effected by different processes, and this conclusion is thought to be consistent with current " molecular " theories of rubber-like elasticity and of the constitution, and viscous flow, of solutions of linear polymers.

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