Model Polyurethane Networks

Abstract Polyurethane model networks have been prepared in various solvents at different polymer concentrations, in such a way that the topology of the networks could be controlled. The effects of the network defects, i.e. unreacted functionalities, closed loops and entanglements, on the theoretical value of the modulus has been estimated and these theoretical values have been compared with the experimentally determined values of the modulus. The results imply that the front factor A in the equation for the free energy of deformation of the network tends to half rather than unity. In dry networks the effect of physical entanglements on the modulus of the network appears to be comparable in magnitude to that of chemical crosslinking.