State of gelation of fully conjugated conducting gels. Gel fraction, swelling, and nuclear magnetic relaxation

Statistical properties of well-defined fully conjugated poly(3-octylthiophene) (POT) gels are explored above glass transition and fusion temperatures by varying the cross-link functionality, f, and the cross-link concentration, R-i. Four series of gels are prepared using four different cross-linking agents. The state of gel connectivity, characterized by the gel fraction is found to depend on the distance to the gelation threshold, epsilon, expressed within a mean-field percolation approach. In the range of explored crosslink densities, H-1 NMR and swelling experiments reveal that the active structural strands of both dry and swollen gels are the linear chain segments defined by adjacent cross-links. These segments are disengaged from one another in swollen gels. The two variables, chain segment contour length and epsilon, are functions of the product fR(i). This parameter is the relevant variable for the description of POT gel structures: master curves of the quantities gel fraction, swelling ratio, and H-1 transverse relaxation rate are obtained versus fR(i).