## LSU Historical Dissertations and Theses

1990

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Chemistry

William H. Daly

#### Abstract

The synthesis and characterization of linear and star branched poly($\gamma$-stearyl-L-glutamate) (PSLG) is reported. A new synthesis for N-carboxyanhydride (NCA) monomers was developed by employing bis(trichloromethyl)carbonate (triphosgene) to functionalize the corresponding $\alpha$-amino acid. Multi-functional primary amino initiators (central units) were synthesized to enable the production of three, four, six and nine arm star polymers by reaction of the central units with the desired NCA. Linear PSLG was produced by either sodium methoxide initiation or benzyl amine initiation of $\gamma$-stearyl-L-glutamate-N-carboxyanhydride (SLGNCA). The highest molecular weight polymers were produced from methoxide initiation. Other molecular weights can be produced from the same ratio of methoxide to monomer by varying the initial concentration of the monomer in the reaction. The polymers were characterized by $\sp1$H and $\sp{13}$C nuclear magnetic resonance (NMR), infrared spectroscopy (IR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), dynamic and static laser light scattering (DLS and SLS), and to a lesser extent by light microscopy. Also, molecular models of both the linear and the star polymers were produced using SYBYL. DSC analysis reveals two endothermic transitions; the lower temperature transition corresponding to the melting of the side chains and the second transition corresponding to a liquid crystalline phase transition of the melted polymer. SLS yielded weight average molecular weight, radius of gyration, and 2nd virial coefficient. From these data and corresponding DLS measurements, other PSLG dimensions were calculated such as the diameter, the hydrodynamic radius, and the length. A Mark-Houwink plot was constructed from the linear PSLG data. The lower functionality PSLG star polymers exhibit negative values for the 2nd virial coefficient when measured in tetrahydrofuran (THF) which is indicative of aggregation. DLS supported this interpretation of the virial coefficient. DSC thermograms also indicate a phase transition at about 68$\sp\circ$C for the high molecular weight stars. GPC analysis of linear PSLG yielded a GPC calibration curve as well an indication of their polydispersity.

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