Dimensional and conformational properties of pullulan tris(alkylcarbamate)s in tetrahydrofuran

Abstract

Pullulan tris(n-butylcarbamate) (PTBC) and pullulan tris(ethylcarbamate) (PTEC) samples with different weight-average molar masses M_w were prepared from pullulan samples with varying chain lengths. Size-exclusion chromatography equipped with multi-angle light scattering detectors (SEC-MALS), small-angle X-ray scattering (SAXS), and viscometry were performed on the samples in tetrahydrofuran (THF) at 25 °C to determine M_w, form factor P(q), radius of gyration R_g, second virial coefficient, and intrinsic viscosity [η]. Infrared absorption measurements were also conducted to investigate the intramolecular hydrogen bonding between the CO and NH groups on adjacent monomer units. The obtained P(q), R_g, and [η] data were analyzed using the wormlike chain model with excluded volume effects, primarily to determine the contour length per monomer unit and the Kuhn segment length L_K, a measure of chain stiffness. The latter parameter L_K values were found to be 10 nm and 8 nm for PTBC and PTEC, respectively. The resulting chain stiffness was significantly lower than that of the corresponding amylose derivatives. Notably, PTBC and PTEC exhibited few intramolecular hydrogen bonding, in contrast to previously investigated amylose derivatives. This characteristic feature suggests that the free polar groups in pullulan derivatives could offer potential applications as macromolecular recognition materials.