Synthesis and Solid-State Characterization of Amphiphilic Tail-End Pyridinium Polymethacrylates

Abstract

The synthesis of a new series of cationic tail-end polyamphiphiles of the type, poly(ω-pyridinium alkyl methacrylate)s with various 4-substituted pyridinium bromide groups and with spacers of 8, 12, and 16 methylene units, obtained by free radical polymerization in aqueous micellar solution, is described, and the thermal and structural characteristics in the solid-state have been studied. All of the polymers show a single glass transition in the range 39−105 °C, whose value depends strongly both on the spacer length, due to internal plasticization, and on the specific nature of the pyridinium moiety, where higher Tg's can be related to greater rigidity of the pyridinium group. The polymers are all birefringent between crossed polarizers, in some cases up to their degradation temperatures. X-ray diffraction investigations indicate that they tend to self-organize into an amorphous lamellar morphology that appears to be better defined the longer the alkyl spacer and whose details depend also on the specific pyridinium moiety. Thus, it is shown that the effects of ionic interactions and of the amphiphilic character of the polymers on their thermal and structural properties are clearly modulated by the alkyl spacer length and by mesogen-related parameters such as rigidity and bulkiness.