GELS OF 2-STEP RIGID POLYAMIDE NETWORKS

Gels of two-step networks were made by first preparing linear polyamides with reactive sites along the chain and then cross-linking by reacting them in solution with connector species in a second step. By using stiff, linear polyamide chains and connector species of varying rigidity, we prepared here gels of fully rigid, semirigid, and semiflexible networks. We then studied their behavior. When all the accessible reactive sites on the chain and all the end groups of the connector species are reacted, a defect-free network is obtained. When low-defect gels of two-step fully rigid and semirigid networks are swollen to equilibrium in a good solvent, their modulus increases above its magnitude in the higher concentration "as-prepared" state. This is contrary to the cases of semiflexible networks, highly defective rigid networks, and "normal" flexible networks. The above unique behavior is due to the fact that in the swollen low-defect rigid network gels most of the stiff segments are straight and cannot stretch further, while in the as-prepared gels a significant fraction of the stiff segments are bent, allowing for straightening, gel swelling, and easier deformation. A description of the structure of the two-step rigid networks and their defects is presented.