Synthesis of amphiphilic cationic copolymers poly[2‐(methacryloyloxy)ethyl trimethylammonium chloride‐co‐stearyl methacrylate] and their self‐assembly behavior in water and water‐ethanol mixtures

A series of amphiphilic cationic random copolymers, namely poly2‐(methacryloyloxy)ethyl trimethylammonium chloride‐co‐stearyl methacrylate] or poly(MADQUAT‐co‐SMA), have been synthesized via conventional free‐radical copolymerization using 2,2′‐azobisisobutyronitrile (AIBN) as initiator and n‐dodecanethiol as chain transfer agent. The resultant products were then characterized by FT‐IR, ¹H NMR, MALDI‐TOF MS measurements. From the number‐average molecular weights of the copolymers, we can conclude that these copolymers have oligomeric structure with a limited number of hydrophilic and hydrophobic moieties in a short polymer chain. The reactivity ratios (r_MADQUAT = 0.83, r_SMA = 0.25) between the hydrophilic MADQUAT monomer and the hydrophobic SMA monomer were calculated by the Finemann and Ross method, which was based on the results of ¹H NMR analysis. The surface activity of the random copolymers was studied by the combination of surface tension and contact angle measurement, and the results indicated that these copolymers possess relatively high surface activity. The critical aggregation concentrations (cac) of the copolymers in aqueous solution were determined by fluorescence probe method as well as surface tension measurement. The different nanoparticles of poly(MADQUAT‐co‐SMA) copolymers formed in pure water or ethanol‐water mixture were proved by the particle size and size distribution in the measurement of dynamic light scattering (DLS). Furthermore, using transmission electron microscopy (TEM), we could observe various self‐assembly morphologies of these random copolymer. All these results show that the amphiphilic cationic random copolymers have a good self‐assembly behavior, even if they are ill‐defined copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4670–4684, 2009