(29d) Effect of Cyclic Defects on the Mechanical Properties of End-Linked Polymer Networks

The phantom network theory and the affine network theory have both been developed to relate the modulus of a polymer network to the density of elastically effective chains, ν. Both theories predict that the shear modulus of a gel, G', can be quantified by the equation G' = CνkT, where kT is the thermal energy and C is a constant that has a value of 1 for the affine network model and 1-2/f for the phantom network model, where f is the functionality of network junctions. Unfortunately, the validity of these theories has not been demonstrated experimentally due to difficulty of quantifying ν. In this presentation, I will introduce our recent development on the quantification of elastically inactive defects, specifically primary loops, in trifunctional and tetrafunctional end-linked networks. This quantification method is based on the mass spectroscopy measurement of purposefully mass-labeled degradation products from the original polymer networks. Mechanical properties of trifunctional and tetrafunctional gels containing various loop fractions were then tested by oscillatory rheology. The fraction of elastically ineffective chains measured using our analytical paradigm allows us to determine the contribution of molecular defects to mechanical property. This work is the first demonstration of the direct effect of primary loop on the mechanical properties of end-linked polymer networks. In addition, rate theory and Monte Carlo theory models were both employed not only for validating the analysis method but also calculating higher order molecular defects to provide more thorough realization.