KINETICS AND RELAXATION OF END CROSS-LINKED POLYMER NETWORKS

The kinetics of end crosslinking in linear polymer melts and the dynamics of the resulting networks is studied using molecular dynamics simulations. Starting from an equilibrated melt, tri- and tetrafunctional crosslinkers are attached randomly to a fraction x of the chain ends. When a free end comes within a short capture distance r(x) from an unsaturated crosslinker, the chain ends are attached. With a stoichmetric number x(s) of crosslinkers present, the long time kinetics of the number of free ends and number of unsaturated crosslinkers decay as a power law in time t-alpha, with a almost-equal-to 0.5. For x not-equal x(s), the decay is significantly faster. These ''model'' networks are then used to show that entanglements play an important role in determining the elastic modulus of the network.