Pressure-volume properties of endlinked hard-chain polymer networks

Equilibrium molecular dynamics simulations are used to obtain the pressure and configurational chain properties of near-perfect, off-lattice, trifunct ional hard-chain networks of chain lengths 20, 35, 50, and 100, and of tetr afunctional hard-chain networks of chain lengths 20, 35, and 50 over a rang e of packing fractions. Our simulation results show that the variation of n etwork pressure with density is similar to that of uncrosslinked chain syst ems of the same chain length, except at low densities where the network pre ssure shows a negative region, as first observed by Escobedo and de Pablo. We present a theoretical treatment leading to an analytical expression for the network pressure as the sum of liquid-like and elastic contributions. T he liquid-like contribution is obtained by extending the generalized Flory- dimer theory to networks, and the elastic contribution is obtained by treat ing the network as a set of interpenetrated dendrimers and using an ideal c hain-spring analogy to calculate the free energy. The theoretical predictio ns for network pressure are in good agreement with simulation data. (C) 199 9 American Institute of Physics. [S0021-9606(99)51615-2].