Gelation and percolation : swelling effect

Abstract
Small angle neutron scattering experiments were performed on Polyurethane branched polymers synthetized near the gelation threshold. The exponent τ of the size distribution function is measured, on a system cross-linked by polycondensation. We find τ = 2.2 ± 0.04. This leads to a fractal dimension for the polymers in the reaction bath Dp = 2.5 ± 0.09, in agreement with percolation model. In the dilute state, the fractal dimension is D = 1.98 ± 0.03, in agreement with recent predictions. Thus the largest branched polymers are swollen by dilution, and behave as lattice animals

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