Size and mass determination of clusters obtained by polycondensation near the gelation threshold

Abstract

The gelification process by polycondensation leading to self similar clusters of polyurethane is studied, near and below the gelation threshold. In dilute solutions, where light scattering experiments are performed, the interaction between clusters is a function of ε, the distance to the gelation threshold. This is a direct evidence of the swelling of the clusters. Thus, the experimental value of the exponent which links the size of the largest clusters to the distance from the gel point ε is larger than the value predicted by the percolation theory. However, the exponent γ, which links the weight average molecular weight to ε, is determined and found to be equal to 1.71 ∓ 0.06, in agreement with percolation theory. The gelification process by polycondensation and percolation belong to the same class of universality : they share two exponent values τ and γ