Impact of Molecular Weight on the Infrared Absorption Behavior of Poly(γ‐benzyl‐L‐glutamate) at Low Degrees of Polymerization

The relationship between the number of repeat units and infrared absorption was investigated for low molecular weight poly(γ‐benzyl ‐L ‐glutamate). From its corresponding N‐ carboxyanhydride, PBLGs were synthesized via ring opening polymerization. The molecular weight was controlled by [monomer]:[initiator] ratios. Using the stretching frequencies of the carbonyl group at 1650 cm −1 and N─H group at 3290 cm −1 , the graph of absorbance versus degrees of polymerization showed a 30% and 45%, respectively increase in absorption. This relationship was confirmed statistically through the Spearman's rank correlation of 0.89 (1650 cm −1 band) and 0.94 (3290 cm −1 band) which indicate a strong, monotonic correlation for both groups. The integration values of the polymer absorbance bands remained constant across all chain lengths, indicating the absorbed energy was also constant. The full‐width‐half‐maximum (FWHM) of the absorbance bands decreased as the degrees of polymerization increased and was confirmed statistically.