Aggregation of Hydrophobically End-Capped Poly(ethylene oxide) in Aqueous Solutions. Fluorescence and Light-Scattering Studies

Abstract

The association of a monodisperse model associative polymer, hydrophobically end-capped poly(ethylene oxide), denoted C12EO460C12, in aqueous solution has been studied. The macroscopic properties have been investigated by rheological methods and correlated to properties on the microscopic level, as revealed from fluorescence and light scattering. The C12EO460C12 polymer associates in water through its hydrophobic end groups and gives rise to a sharp increase in viscosity at about 2 × 10-2 g mL-1 due to formation of large aggregates or networks. The aggregation starts, however, at much lower concentrations. Already at 0.5 × 10-2 g mL-1 hydrophobic domains large enough to dissolve pyrene have formed. The aggregation process is very gradual without a distinct cmc. An estimate of the aggregation number of the hydrophobic domains obtained from fluorescence is about 15−30 end groups per micelle. The distribution of relaxation times from DLS shows three important diffusive modes in the concentration range 3 × 10-3 to 5 × 10-2 g mL-1. A fast mode in the dilute region is attributed to unimers or small oligomeric aggregates of C12EO460C12. At concentrations near the point where the viscosity rises an intermediate mode appears. This mode is considered to reflect the cooperative motions of the formed network. In the whole concentration range studied a slow mode is present. In the dilute region this mode dissappears completely upon addition of salt and is therefore attributed to the PEO interchain interaction. In the high-concentration region, however, this mode is probably also influenced by the aggregation of the hydrophobic ends of C12EO460C12. The validity of these results is discussed and compared with a model considering the gain/loss of free energy upon formation of aggregates (loops, oligomeric aggregates, and micelles).

Self‐assembly and responsiveness of polypeptide‐based block copolymers: How “Smart” behavior and topological complexity yield unique assembly in aqueous media

“…Our group recently reported spherical micelle formation for poly(propylene oxide) 44 -b-poly(L-Lys) 217 and poly(butadiene) 107 -b-poly(LLys) 200 block copolymers. 11,62 By performing in-depth light scattering studies, we were able to calculate a hydrophobic core size based on the aggregation number (N agg ) determined from Zimm analysis, assuming a fully dehydrated core.…”

“…Our group reported rod-like micelle formation for PB-b-PLys block copolymers with a PLys fraction in the vicinity of either a rod-like or spherical micelle assembly behavior. 62 Figure 5 shows a plot of R h versus pH for PB 107 b-PLys 100 and PB 60 -b-PLys 50 . At pH above 4, the assemblies exist as large rod-like micelles or a mixture of rod-like and spherical micelles, with the size decreasing from low to high pH from deprotonation of the PLys side chains.…”

“…In general, the helical, rod-like nature of the peptide results in a flatter interface, which favors vesicle of fibril formation. [77][78][79][80][81][82][83][84][85] FIGURE 5 R h vs. pH plots for PB 107 [83][84][85] In their research, they studied assemblies formed from poly(c-benzyl-L-glutamate) 23 -b-hyaluronan 10 (PBLG 23 -b-HYA 10 , polypeptide-bpolysaccharide) polysaccharide. They denote that the PBLG block was chosen to guarantee the formation of vesicles, whereby its rigid, helical nature leads to close packing of helices which serves to favor flatter interface morphologies (Fig.…”

“…105,106 Assembly Behavior of BAB Linear Triblock Copolymers with a Responsive Polypeptide Inner Block The aqueous self-assembly behavior of linear triblock BAB copolymers has been evaluated widely for synthetic coilcoil-coil type systems. [107][108][109][110][111] These type of systems are reported to aggregate into sunflower micelles, enabled by molecular bending of a flexible middle block, in dilute solution. 108,111 At higher concentrations, these systems often form network structures from the association of corona chains between micelles resulting in hydrogelation.…”

“…108,111 At higher concentrations, these systems often form network structures from the association of corona chains between micelles resulting in hydrogelation. 107,109,110,112,113 A few studies have been devoted to self-assembly of coil-rod-coil BAB triblock copolymers containing a functionalized, hydrophilic gold nanorod center FEATURE ARTICLE block and hydrophobic coil outer blocks. [114][115][116] This category of amphiphilic molecules exhibited self-assembly into ''doughnut-like" supramolecular barrels (similar to toroid micelles), as a result of stiffness from the center block.…”