Micellar ROMP

Optoelectronic applications were also targeted with ROMP amphiphilic copolymers synthesized from NBE-substituted oligothiophene amides [78]. An extended conjugated system across the amide bonds linking the thiophene rings was reported, enabling the formation of a new class of micellar chromophores. 

Figure 6.1 Graft-through approach to micellar nanoparticles via ROMP (M = Ru or Mo catalyst) and chemical structures of the most popular catalysts employed for ROMP.

Here, the distinct domains of the resulting hybrid polymer are responsible for the self-assembly of the material. It should be noted that there are several other approaches to nanomaterials via ROMP, including the synthesis of dispersed latex nanoparticles, [29-34] hybrid nanoparticles via scaffolded initiation [35-39], and nanoparticles encapsulated in polymer matrices [40,41]. Amphiphilic micellar nanoparticles are by far the most prevalent systems in the literature relevant to a discussion of ROMP in nanoparticle synthesis, particularly those fully characterized in terms of particle formation and morphological characterization of the resulting polymer aggregates. Amphiphilic copolymers synthesized by ROMP that are not studied in this manner [42-45] or those nanoscale architectures involving only covalent interactions [46, 47] are not discussed here. 

Gianneschi and coworkers [74] demonstrated that peptides could also be polymerized via ROMP as the hydrophihc domain of an amphiphilic block copolymer in order to yield micellar nanoparticles of various sizes depending on the size and composition of each block. NBE-modified peptides were polymerized as the hydrophihc block, along with a phenyl NBE derivative to serve as the hydrophobic block of the amphiphile. The resulting polymers, termed peptide polymer amphiphUes (PPAs), formed spherical miceUes on the order of 20—SOOnm in diameter (Figure 6.18). 

Due to it s highly efficient and orthogonal nature, copper-catalyzed click chemistry is an attractive route to post-polymerization functionalization of ROMP copolymer backbones yielding amphiphilic micellar nanoparticles [103, 104]. However, it should be noted that post polymerization modification is necessary to yield azide or acetylene modified polymers, as azide and acetylene functionalities are not compatible with current ROMP catalysts. Ohe and coworkers [104] have synthesized amphiphihc triblock copolymers capable of assembly into discrete micellar nanoparticles by clicking an acetylene-modified hexaethylene... 

To expand the variety of monomers available for polymerization and to increase the range of copolymer and nanoparticle architectures, attention has turned toward the development of methods whereby multiple polymerization techniques can be utilized to generate unique and functionally diverse materials. The grafting-from (Figure 6.29) approaches to ROMP-based micellar... 

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