(607a) Predicting the Plateau Modulus from Molecular Parameters of Conjugated Polymers

The relationship between Kuhn length b, packing length p, and plateau modulus G_N^° initially proposed by Graessley and Edwards and experimentally investigated by Everaers, while well-studied for flexible and stiff polymers, has a large gap in experimental data between the flexible and stiff regimes. This gap prevents the validation of theoretical models of the crossover between flexible and stiff polymers and therefore, the prediction of mechanical properties from chain structure of any polymer in this region. Given the chain architecture, including a semiflexible backbone and side chains, conjugated polymers are an ideal class of material to study this cross-over region. Conjugated polymers are used in many organic electronic devices such as organic photovoltaics, organic light emitting diodes, organic field effect transistors and bioelectronics. However, fundamental characteristics of these materials, such as mechanical properties and phase behavior, and their correlation with chemical structure are not well understood. This prevents the formation of rational design systems that could accelerate progress in producing conjugated polymers with electronic and mechanical properties that are application specific. Using small angle neutron scattering (SANS), static light scattering (SLS), and oscillatory shear rheology along with the freely rotating chain model we have shown that nine amorphous and isotropic conjugated polymers and three aromatic polymers not only populate a large part of the gap between flexible and stiff regimes, but that they follow the proposed relationship between b, p, and G_N^°as well which allows for better predictions of mechanical properties from the structure of conjugated polymers in future.