Mesophase structures of solid poly(N-alkylacrylamides) as revealed by SAXS

Small angle X-ray scattering (SAXS) on films of poly(N-alkylacrylamides) wi th various chain lengths reveals that these well known polymers exhibit a m icrophase-separated solid-slate structure with liquid crystalline order. An alysis of the phase morphology in dependence on the alkyl side chain length results in the following scenario: For the Cg and Clo tail, the microphase s are just weakly developed and quantitative analysis of the broad scatteri ng peak reveals an ill-defined structure without sharp phase boundaries. Fo r the C-12 and C-14 derivative, we found a well developed mesophase, which shows a number of scattering peaks and cannot be related to any classical p hase morphology. For these two materials, a phase model is developed on the base of a new technique of quantitative evaluation of the X-ray data. Poly (N-hexadecylacrylamide) and poly(N-octadecylacrylamide) exhibit lamellar mo rphologies with low long range order. Poly(N-octadecylacrylamide) obtained by polymerization instead of polymer reaction exhibits a different phase mo rphology which resembles the so-called sponge-like phase. The different pha se morphologies are also reflected in the thermal behavior where the sponge phase shows a lower melting point and melting enthalpy of the side chains than the lamellar mesophases, regardless of the longer alkyl chains involve d in this system.