## LSU Historical Dissertations and Theses

1995

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Chemistry

William H. Daly

#### Abstract

As most polypeptides, poly($\gamma$-alkyl-$\alpha$,L-glutamates) exhibit the ability to exist in well defined chain conformations of extensive order such as the $\alpha$-helix. This helical conformation imparts a rod-like character to the polymer which is maintained in the melt and in certain solvents at particular concentrations. This dissertation reports the synthesis and characterization of poly($\gamma$-alkyl-$\alpha$,L-glutamates), in particular, of poly($\gamma$-stearyl-$\alpha$,L-glutamate) (PSLG), poly($\gamma$-benzyl-$\alpha$,L-glutamate) (PBLG), and poly($\gamma$-stearyl-$\alpha$,L-glutamate)-co-poly$(\gamma$-benzyl-$\alpha$,L-glutamate). Polymerization studies of PSLG with primary, tertiary, and silylated amines as initiators; and PBLG with coinitiators are described. The labeling of PSLG with a fluorescein dye is also explained. All the polymers were obtained from the corresponding N-carboxyanhydride monomers. Special focus was given to nearly monodispersed samples of PSLG. Polydisperse samples of PSLG were fractionated using a tetrahydrofuran-methanol system to obtain fractions with polydispersities of 1.1 to 1.7. The nearly monodispersed PSLG samples were characterized by $\sp1$H-NMR, gel permeation chromatography, static light scattering, and intrinsic viscosity studies. Formation of lyotropic liquid crystalline phases of the nearly monodispersed samples of PSLG in tetrahydrofuran were studied by optical microscopy. The isotropic and cholesteric liquid crystalline phases are detected using cross polarizers. The biphasic region is manifested by the presence of spherulites. The phase boundaries for PSLG of different molecular weights were determined. The reactivity of trimethylsilyl iodide with ester groups was used for the modification of the side chains of PBLG. The trimethylsilyl ester formed reacts with isocyanate groups under neutral conditions at room temperature to form amides. Formation of crosslinks between polymer chains using 1,6-diisocyanatohexane produces isotropic gels made of rigid rods. The gelation process can be followed by dynamic light scattering. The formation of anisotropic, highly ordered gels (crosslinking of the polymer in the liquid crystalline phase) is accomplished by applying an electric field while the gelation occurs.

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