The effect of degree of polymerization on intra- and interchain micellization of a tail-type cationic polysoap

Abstract

We have used Reversible Addition Fragmentation chain Transfer (RAFT) to polymerize the T-type surfactant monomer α,ω-methacryloylundecyltrimethylammonium bromide (MUTAB) to various degrees of polymerization, and thereby investigate how its self-assembly is affected. Small-angle neutron scattering (SANS) shows that the interchain aggregation into micelles with an approximately constant number of MUTAB monomer equivalents occurs at low degrees of polymerization, but that micelle elongation occurs when the degree of polymerization exceeds a critical value. In this regime interchain aggregation gives way to intrachain assembly into unimolecular or “unimer” micelles. As with conventional cationic surfactant solutions, addition of salicylate produces long, worm-like micelles containing many amphiphilic polymer chains at all degrees of polymerization. Oscillatory rheology reveals a transition from scission- to reptation-dominated relaxation as increasing polymer chain length also increases the distance between potential scission points. The measured relaxation times lie in the range of hundredths to a few seconds – thus demonstrating the rapidly equilibrating nature of these micellar systems even at the highest degrees of polymerization achieved.