MONTE-CARLO STUDY OF ASSOCIATIVE POLYMER NETWORKS .1. EQUATION OF STATE

The equation of state of associative polymer networks has been studied by Monte Carlo simulation. To describe the associations, an algorithm is introduced which for dilute monatomic systems reduces to the well-known mass action law. For the polymers, the simple bead spring model was employed. The incorporation of a finite volume of the beads is essential to prevent phase separation once the associative interaction is turned on, and the system is quenched into the gel state. The excess pressure of this quenched state is well described by two exponents of the density p. The repulsive part of the excess pressure scales proportional to p(alpha), the attractive part is proportional to p(8). For the nonassociating polymers we measured the first exponent as alpha=2.339 +/- 0.006, and for associating polymers far away from the critical point we found beta=2.06 +/- 0.05. For certain values of the density and the association constant the measured pressure was negative, in these cases we find microphase separated configurations. The simulations also enabled the establishment of the percolation transition. The association constant at the gel point has been obtained as a function of density and polymer length. Together with the equation of state this resulted in a phase diagram for polymer gels.