## LSU Historical Dissertations and Theses

1997

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Chemistry

William H. Daly

#### Abstract

Poly($\gamma$-benzyl-$\alpha$,L-glutamate), PBLG, is a widely studied example of polypeptides. The preparation of monodisperse samples of PBLG and PBLG oligomer is difficult to achieve. In this work we probe the possibility of preparation of PBLG oligomers by polymerization of L-glutamic acid N-carboxyanhydride (NCA) with different initiators such as primary amine, sterically hindered secondary amine, tertiary amine, and strong base. Information regarding molecular weight distribution of these oligomers was obtained by applying MALDI-TOF mass spectrometry and reversed phase HPLC. While some researchers reported that application of primary amine initiators or polar solvents such as DMF could improve the molecular weight distributions of PBLGs, our research demonstrated that the same was not true for PBLG oligomers. The preparation of monodisperse PBLGs and PBLG oligomers will remain as a rather challenging task because of the complication of the polymerization mechanisms. An alternate route of preparation of highly monodisperse PBLG oligomers, PBLG 4-, 8-, 12-, 16-mers, via a convergent approach by solution phase peptide synthesis is reported. PBLG oligomers with designed length could be obtained via this approach, which is impossible by polymerization of NCAs. Modification of the side chains of the PBLG oligomers is achieved by trimethylsilyl iodide under mild conditions. This modification changes the solubility of the PBLG oligomers, and could be applied for making cross-linking system. Previously, others have synthesized star polymers with rod-like poly($\gamma$-alkyl-$\alpha,$L-glutamate) arms from the N-carboxyanhydride (NCA) monomers and multifunctional primary amine central units with the limitation of different length of arms. In this research we synthesized PBLG-4-mer and PBLG-8-mer star-shaped oligomers with different central units via a convergent approach. The star oligomers were purified by SEC and reversed phase HPLC, and characterized by MALDI-TOF mass spectrometry and reversed phase HPLC.

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