Mechanisms of Deformation in Fully Conjugated Conducting Gels. Stretching and Swelling

Uniaxial elongation and swelling of well-defined fully conjugated poly(3-octylthiophene) gels of various functionalities and cross-link concentrations are studied above the melting temperature. The gels exhibit rubber elasticity (elastic modulus E in the range 0.2 < E < 0.7 MPa) and swell in chloroform. A linear relationship is established between E and the inverse of the mean number of skeletal bonds between consecutive cross-links (1/ N av ). Variations of the transverse relaxation rate of protons attached to the polymer network with 1/ N av are also linear whether NMR observations are performed on dry unconstrained networks or on fully swollen gels. The results show that the active network chain segments which give rise both to elastic and swelling properties are the linear strands comprised between adjacent cross-links. Moreover, we show that when doped by iodine in chloroform these gels are conducting while they remain swollen.