CONCENTRATION-DEPENDENCE OF THE STATIC PROPERTIES OF RANDOMLY BRANCHED POLY(METHYL METHACRYLATE) STUDIED BY STATIC-LIGHT SCATTERING

We study the static properties of solutions of randomly branched poly( methyl methacrylate) (PMMA) obtained near the gelation threshold by me asuring their structure factor using static-light scattering experimen ts. The picture of the initial (not yet diluted) system is consistent with a hierarchical interpenetration of the aggregates, as predicted b y the percolation theory. The dilution creates in the system a charact eristic length dependent on concentration, beyond which excluded-volum e interactions are screened. This length is proportional to the appare nt radius of gyration R(ga). The concentration dependences of R(ga) an d the apparent molar mass M(a) associated with R(ga) are determined by a Guinier analysis of the light scattering data. The self-similarity of the size distribution of the aggregates is clearly shown by the mas ter curve representing the static structure factor of the system S-z(q ) as a function of q . R(ga).