Synthesis, Characterization of Erythromycin Propionate Core-Based Star Poly(ether urethane)s and Their Antibacterial Properties

New four-arm star poly(ether urethanes) (star PUs) based on erythromycin propionate core are presented. Toluene 2,4-diisocyanate (TDI) and 4,4′-methylenebis (phenyl isocyanate) (MDI) as diisocyanates and Terathane of different molecular weights as polyether arms were employed in their synthesis in order to study their structure-property relationship. The synthesized star PUs were analyzed through IR and 1 H NMR spectroscopies, gel permeation chromatography, X-ray diffraction, thermogravimetry, differential scanning calorimetry. The IR spectral changes obtained on heating the samples were investigated. Disc-diffusion method was employed for antimicrobial tests. The values of the glass transition temperature are higher than those of starting polyethers attributable to the influence of the more rigid erythromycin propionate core bearing urethane groups. The melting temperatures corresponding to soft polyether arms are in the melting temperature range of starting polyethers. At higher temperatures melting phenomena associated to hard urethane core are obtained. The IR spectra recorded at various temperatures reveal that the composition of the hard segment having MDI in the structure ensures higher conformation stability during heating process. The crystalline peaks in the X-ray diffractograms are consequence of polyether arms crystallinity. MDI and higher polyether molecular weight increase the thermal stability. The values of hydrodynamic radii increase with increasing polyether arm length and are higher for TDI star PUs than MDI star PU because of the expanded structures of the former ones. The antibacterial study reveals that for hospital S. aureus strain the diameters of inhibition zones are lower than for S. aureus ATCC 25923.