Growth process of polymers near the gelation threshold

We will review experimental results obtained recently on the determination of the laws governing the growth process of polymer clusters as the gel point is approached. The exponent γ which characterizes the increase of the mean weight-average molecular weight M_w as the gel point is approached and the exponent τ which characterizes the mass distribution were measured on different chemical systems. They were found to be independent of the chemical system (within experimental error) and very close to exponent values calculated by computer simulations following the percolation model. Therefore, the sol-gel transition is a critical phenomenon of connectivity belonging to the same class of universality as percolation.