Scaling behavior: Effect of precursor concentration and precursor molecular weight on the modulus and swelling of polymeric networks

End-linked poly(dimethylsiloxane) (PDMS) networks, containing a minimal num ber of defects, are prepared from vinyl-terminated PDMS chains in the prese nce of a theta (theta) solvent. Unreactive tri-methyl terminated PDMS of th e same molecular-weight distribution as the reactive PDMS precursors were c hosen as the theta solvent. Four precursor molecular weights ranging from 1 0 000 to 100 000 daltons were studied. The dependence of the initial modulu s after cure, the dry modulus after solvent extraction, and the degree of e quilibrium swelling on precursor concentration during cure were compared to recent scaling predictions. The experimental scaling exponents were found to be strong functions of the molecular weight of the precursor chains and their values approach the theoretical predictions for high-molecular-weight precursors. The relationship between the modulus of the fully swollen netw ork and the degree of equilibrium swelling is found to be independent of pr ecursor molecular weight and precursor concentration during cure and in bet ter agreement with the corresponding, more robust, theoretical prediction. (C) 2000 The Society of Rheology. [S0148-6055(00)00504-6].