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"Chiral Metallopolymers: Synthesis, Self-Assembly and Applications"

Final Report Summary - CMSSA (Chiral Metallopolymers: Synthesis, Self-Assembly and Applications)

The goals of the project were to synthesize chiral metallopolymers and study their self-assembly and potential applications. During the course of the fellowship, a variety of approaches have been evaluated to fabricate chiral metallopolymers and to introduce chirality into achiral metallopolymers or their micellar self-assembly. Specifically, we have developed a efficient method to transfer chirality to poly(cobaltoceniumethylene) (PCE) polyelectrolytes by forming complexes with a variety of chiral counter-ions.

Highlights include:

1) Water-soluble PCE polyelectrolyte adopted a chiral structure when bound electrostatically with DNA and formed uniform nanoparticles in water. This is the very first example of a chiral metallopolymer complex and was recently published (Chem. Comm. 2013, 49, 42-44).

2) By oxidation of poly(cobaltocenoethylene) in the presence of amino acid-derived chiral anionic surfactant, chiral PCE complexes with enhanced solubility in organic solvent were prepared. The chiral complexes also self-assemble into uniform fiber-like micelles in selective solvents, which turned to be an unique self-assembly example in metallopolymer systems. The manuscript on this work is under preparation and is going to be submitted soon.

Concurrent to the chiral metallopolymer work, research on the self-assembly of polyferrocenylsilane block copolymers was being performed. This research has produced significant scientific results, including the achievements in the controls of hierarchical self-assembly and the preparation of complex micellar structures.

Highlights include:

1) Amphiphilic cylindrical block co-micelles have been synthesized for the first time via crystallization-driven living self-assembly. A variety of superstructures, such as supermicelles, chains, 3D networks can be subsequently obtained by controlling the solvent, micellar block composition, relative length of the micellar blocks, etc.

Preliminary results on the formation of amphiphilic cylindrical B-A-B triblock co-micelles and the formation of supermicelles have been published (Angew. Chem., Int. Ed. 2012, 51, 11882-11885). Manuscripts on the other hierarchical structure are under preparation and will be submitted soon.

2) Multi-armed micelles and block co-micelles with uniform, hierarchical multipod structures were prepared via the crystallization-driven self-assembly of crystalline-coil polyferrocenylsilane block copolymers from nanocrystals of the homopolymer. Coronal crosslinking followed by nanocrystal dissolution led to the release of non-centrosymmetric AB cylindrical diblock co-micelles. This is the first example of ordered multipod structures in soft matter systems and was recently published (J. Am. Chem. Soc. 2013, 135, 12180-12183).

3) Through the growth of thinner-core cylindrical micelles at the termini of the thicker-core cylindrical micelle seeds via living crystallization-driven self-assembly, branched cylindrical micelles with monodisperse middle segments and, in most cases, two branches at the seed terminus were also prepared. After crosslinking of the coronas, the branched micelles become resistant to dissolution in good solvents for both blocks and can be manipulated as swollen, colloidally-stable nanomaterials. Manuscript on this work is under preparation and will be submitted soon.

The proposed transfer of knowledge objectives progressed well throughout the duration of the fellowship. Working in the Manners group, Dr. Qiu has gained significant experience in the areas of polymer synthesis, self-assembly, and characterization of nanoscale objects. Through the supervision of graduated students, Dr. Qiu has been able to transfer knowledge and skill sets to the students.

Dr. Qiu participated in international polymer conferences in China and UK and established collaborative contacts that will be maintained in his future.

The work completed during the course of this fellowship has made a significant impact on the field of metallopolymer and block copolymer self-assembly. As a measure of the impact of Dr. Qiu’s work, his research was recently highlighted in a top-tier, high impact journal (Nature Chem. 2013, 5, 733-734).