Ionomer and mesomorphic behavior in a tail-end, ionic mesogen-containing, comblike copolymer series

A series of homologous statistical polymethacrylate comb copolymers with ta il-end 4-(dimethylamino)pyridinium ionic groups were synthesized by partial quaternization of high molar mass poly( 12-bromododecyl methacrylate). The copolymers of lower ion content are found to be biphasic by differential s canning calorimetry, resembling classical ionomers, with a lower glass tran sition temperature (T-g) that remains constant up to about 20 mol % ion con tent before increasing and a higher T-g that increases monotonically with i on content. X-ray analysis indicates the presence of a soft phase with an i nvariant microstructure for all of the copolymers, whereas the hard-phase m icrostructure, considered to be a disordered partial bilayer in the ionic h omopolymer, is characterized by an increasing long period with decreasing i on content. Models to reconcile the various data are proposed, which show h ow large amounts of nonionic units can be incorporated into the hard-phase microstructure, with the invariant soft-phase microstructure also rationali zed. This copolymer series thus bridges ionomer and mesomorphic polysoap ch aracteristics by the presence of two phases whose relative proportions vary with ion content, both of which possess their own (short-range) microstruc ture that determines the nature of their evolution with copolymer compositi on.