Self-assembled mesomorphic complexes of branched poly(ethylenimine) and dodecylbenzenesulfonic acid

Solid-state complexes of flexible polymers with surfactants (surf) exhibit mesomorphic phase and microphase-separated lamellar morphology. Because the surf molecules are strongly associated with the polymer backbone, the orde red packing of the alkyl tails should be cooperative with the chain packing in the polymer layers which is influenced by chain topology. In this study , the supramolecular structure and thermal properties of the complexes of a highly branched poly(ethylenimine) (PEI) with dodecyl-benzenesulfonic acid (DBSA) were investigated. Polarized optical microscopy and small-angle X-r ay scattering (SAXS) revealed the presences of mesomorphic phases and micro phase-separated lamellar morphology in the complexes. The ordered supramole cular structure was observed not only for the stoichiometric composition bu t over a wide composition range. The thicknesses of polymer and surf layers were determined from the one-dimensional correlation function. The surf la yer thickness varied with complex composition. The glass transition tempera ture of polymer layers was raised by complexation because of the stiffening of polymer chains. Complexation with DBSA also enhanced the thermal stabil ity of PEI, where the thermal decomposition temperature can be raised by as much as 50 degrees C.