Date of Award
2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
Committee Chair
Carmen Scholz
Committee Member
Bernhard Vogler
Committee Member
Pamela Twigg
Committee Member
Judith Schneider
Committee Member
Paul S. Russo
Research Advisor
Carmen Scholz
Subject(s)
Molecular weights, Glutamic acid polymers, Nuclear magnetic resonance spectroscopy, Infrared spectroscopy
Abstract
Acquiring the molecular weight of a polymer is not a trivial task due to the differing degrees of chain growth within a sample during synthesis, leading to a molecular weight range instead of a single value. Popular methods that estimate a polymer’s molecular weight include proton nuclear magnetic resonance, gel permeation chromatography and mass spectrometry; however, these methods have drawbacks like molecular weight limitations, dispersity limitations and column dependencies. Since poly(amino acid)s are used in biomedical research, developing a harmonizing set of molecular weight characterization methods is crucial. Two novel methods for estimating the molecular weight by infrared absorbance and through diffusion coefficients were investigated for poly(γ-benzyl-L-glutamate) (PBLG) at low degrees of polymerization (< 11000 gmol−1). From its corresponding N -carboxyanhydride, PBLGs were synthesized via ring opening polymerization, and the molecular weights were controlled by [monomer]:[initiator] ratios and characterized by 1H-NMR and MALDI-TOF. With little previous work on explicitly investigating if a relationship between absorbance and molecular weight for polymers exists, statistically rigorous methods were used to confirm or deny the relation using PBLG as the model polymer. Using Spearman’s rank correlation coefficients and p-values, a strong correlation between absorbance and molecular weight in chloroform was statistically confirmed. The integration values of the polymer absorption bands remained constant across all chain lengths, and the full-width-half-maximum of the absorbance bands decreased with increasing DP. Diffusion-ordered NMR (DOSY) provides the opportunity to obtain information regarding the molecular weight, purity and polydispersity of polymers in one characterization technique. Four mathematical models (unmodified, small molecule, species comparison and power law) for estimating the molecular weight through the diffusion coefficient obtained in 1. DMSO-d6 and 2. CDCl3 were compared using the percent change of the 1H-NMR/MALDI-TOF molecular weight and the model molecular weight. The unmodified diffusion coefficient-molecular weight relation proved to be linear, and this model/regression produced the lowest percent changes. The diffusion coefficients were then used to calculate the polydispersity indexes and were found to be in excellent agreement with those obtained by MALDI-TOF. DOSY NMR also provided a complementary method to traditional intrinsic viscosity experiments for determining points of chain entanglement of low molecular weight PBLG.
Recommended Citation
Johnson, Leah C., "Synthesis and characterization of poly(γ-benzyl-L-glutamate) by infrared absorption and diffusion-ordered NMR spectroscopy" (2026). Dissertations. 481.
https://louis.uah.edu/uah-dissertations/481
Comments
Synthesis and characterization of poly(y-benzyl-L-glutamate) by infrared absorption and diffusion-ordered NMR spectroscopy