Polymerizable Cationic Micelles Form Cylinders at Intermediate Conversions

Abstract

The structural evolution of micelles of the polymerizable surfactant omega-methacryloyloxyundecyltrimethylammonium bromide (MUTAB) during UV-initiated polymerization in aqueous micellar solution has been followed by small-angle neutron scattering. Although the micelles are short spheroids both before and after polymerization, a significant, distinct population of rodlike micelles develops during the reaction, which accounts for as much as 40 vol % of the micellized surfactant and coexists with the spheroids and dissolved monomer. These coexisting micelle populations are shown to remain in dynamic equilibrium throughout the reaction and can be understood by treating it as a ternary mixture of surfactant, amphiphilic polyelectrolyte, and water.

Pulsed laser studies of cationic reactive surfactant radical propagation kinetics

“…The particle size distributions for 10 wt% macromonomer aqueous solutions at 25 and 70 °C, shown by Figure S7 provide evidence for PCL2ChMA compartmentalization, where the bimodal intensity scattering could indicate that PCL2ChMA micelles may have non-spherical geometries, 49 as was observed for polymer produced by PCLnChMA homopolymerization 47 and as has been documented for micelles of the chemically similar MUTAB surfmer. [18][19][20] In addition, the dispersion parameters summarized by Table S2 highlight the dynamic nature of the system; in particular, the decreasing as well as a measured decrease in the EA for kp of partially and fully ionized MAA aqueous homopropagation systems. 37 As a further indication that PCL2ChMA aqueous propagation is prominent at 85 °C, the secondary (non-PLP) peaks of the MMDs of Figure 3 shift with increasing NaCl concentrations from logM = 7.0 towards logM = 5.7 and then to logM = 4.5.…”

“…Indeed, for the MRP of cationic tail-type surfmer, ωmethacryloyloxyundecyltrimethylammonium bromide (MUTAB), with concentration twice its CMC at 25 °C, Chatjaroenpron et al showed that the presence of unpolymerized MUTAB micelles and a constant concentration of free aqueous MUTAB were maintained up to ≈ 50% conversion, confirming that poly(MUTAB) micelles grow at the expense of the unpolymerized ones. 18 In terms of morphology, unpolymerized and fully polymerized MUTAB micelles are spheroidal (i.e., geometries with long and short radii ranging roughly from 10-100 Å and 10-20 Å, respectively),…”

“…while at intermediate conversions rod-like mixed polymer/monomer micelles (with length and cross-section radius ranging roughly from 200-3000 Å and 10-30 Å, respectively) coexist in dynamic equilibrium with unpolymerized micelles. [18][19][20] The structures of poly(MUTAB) systems are also sensitive to environmental factors, responding dynamically and reversibly to temperature, counterion, and salt addition. 21 Furthermore, as suggested by Hamid and Sherrington, 22 cationic tail-type surfmers, such as MUTAB, can adopt a "looped" or "hairpin" conformation where both cationic head and polar methacrylate tail reside at the micelle/water interface.…”

“…However, negligible differences in the quality of PLP structure for experiments performed to high conversions suggests that at 25 °C the compartmentalized propagation occurs at constant macromonomer concentration. Therefore, it is reasonable to assume that during polymerization at 25 °C (and up to at least 28% conversion), an equilibrium, or saturated, PCL2ChMA concentration at the compartmentalized reaction site is maintained via macromonomer diffusion from unpolymerized micelles 14,17,18.…”

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

“…1) remain in thermodynamic equilibrium throughout the in situ polymerization process. [17][18][19] It forms small spheroidal micelles before polymerization (N agg ¼ 42) and larger spheroids aer polymerization with a four-fold increase in length, but only a minor increase in the cross-sectional radius. At intermediate polymer conversions, rod-like micelles form with lengths of more than 1500 Å, which collapse into polymerized spheroids as the monomer is consumed.…”