Covalent vs Metallo-supramolecular Block Copolymer Micelles

Abstract

An amphiphilic metallo-supramolecular polystyrene-block-poly(ethylene oxide) diblock copolymer containing a bis(2,2‘:6‘,2‘ ‘-terpyridine)ruthenium(II) complex (PS20-[Ru]-PEO70) as a supramolecular connection between the two constituting blocks has been compared to the covalently bonded counterpart (PS22-b-PEO70). The two different copolymers have been used to prepare kinetically frozen aqueous micelles that consist of a glassy polystyrene core surrounded by a poly(ethylene oxide) corona. The micelles have been characterized by dynamic light scattering (DLS). In the case of the PS22-b-PEO70 copolymer, micelles with a hydrodynamic diameter (D h) of 18 nm are observed while stable micelles with a D h of 65 nm and larger aggregates are formed for the PS20-[Ru]-PEO70 sample. Addition of different salts during the initial stage of micelle formation has a deep effect on the final micellar characteristic features, which are now similar to the ones of the covalent system. This effect is attributed to a decreased electrostatic repulsion between the charged bis(2,2‘:6‘,2‘ ‘-terpyridine)ruthenium(II) complexes which are present at the interface between the immiscible polystyrene and poly(ethylene oxide) blocks. Furthermore, addition of different salts to solutions of the PS20-[Ru]-PEO70 micelles, initially prepared in the absence of salt, caused a decrease of their size, although the packing of the charged bis(2,2‘:6‘,2‘ ‘-terpyridine)ruthenium(II) complexes could not be changed in these kinetically frozen micelles. A decrease in micelle size has also been observed as temperature increases. These effects have not been observed in the covalently connected counterpart and are thought to originate from stretched poly(ethylene oxide) chain segments. A model for metallo-supramolecular micelles is tentatively proposed that takes into account the experimental observations.

Metal–Ligand‐Containing Polymers: Terpyridine as the Supramolecular Unit

“…The inherent viscosity of the copolymer solutions decreased with the complexation with Fe(II) suggesting polymer chain shrinkage. In recent years, Fraser and coworkers, [35][36][37][38][39][40] Schubert and co-workers, [8,[41][42][43][44][45][46][47][48][49][50][51] Sleiman and co-workers, [52][53][54] Calzai and Tew [55] ,and Weck and co-workers, [56][57][58][59][60] among others have became interested in more precise polymer architectures by employing controlled polymerization techniques (see Figure 4). Their focus has been on the noncovalent functionalization with metal complexes and hydrogen bonding to achieve multistep and orthogonal self-assembly.…”

Monte Carlo Simulations of Metallo‐Supramolecular Micelles

“…[4][5][6][7][8][9][10][11][12] Due to the heterogeneous structure of their building blocks, metallo-supramolecular micelles exhibit unprecedented capabilities. [3,13] For example, electrochemical, photochemical, and redox properties associated with metal-ligand complexation [14] can be further exploited in metallo-supramolecular micelles to monitor and control material properties. The advanced properties of the metallo-supramolecular micelles which result from the interplay between the metal-ligand complexation and the volume interactions between blocks of metallo-block copolymers and/or solvent make their characterization more difficult and understanding of the underlying mechanisms of their behavior more challenging.…”

Tuning the Thermotropic and Lyotropic Properties of Liquid‐Crystalline Terpyridine Ligands

“…[25] The resulting complexes have many potential applications in fields such as macromolecular chemistry, biochemistry, photophysics, and nanoscience. In particular, terpy and its multiple derivatives have been used advantageously as building blocks for the engineering of novel supramolecular structures such as spiral lines, [26] dendrimers, [27] micelles, [28] polymers, [29,30] and liquid-crystalline soft materials. [31] Formation of ordered architectures on surfaces, [32][33][34] functional molecular devices, [35] and biochemical applications [36] are particularly challenging.…”