A green
route is presented to synthesize bio-based nonisocyanate
thermoplastic polyoxamide-ureas (POXAUs) containing flexible poly(propylene
oxide) segments. A hexanedioxamide-diester (HDODE) was synthesized
from the reaction of 1,6-hexanediamine with excessive diethyl oxalate.
Four H2N– terminated polyoxamide prepolymers (PrePOXAs)
were synthesized through melt polycondensation of HDODE with O,O′-bis(2-aminopropyl) poly(propylene
glycol). Chain extension of PrePOXAs was conducted with bis(hydroxyethyl)
hexanediurethane as a chain extender, and four chain-extended POXAs
or POXAUs were prepared. The POXAUs were characterized by size exclusion
chromatography, Fourier transform infrared, 1H NMR, wide-angle
X-ray scattering, differential scanning calorimetry, thermogravimetric
analysis, and tensile testing. POXAUs show Mn
up to 29 900 g mol–1, melting temperature
from 148 to 156 °C, initial decomposition over 242 °C, tensile
strength up to 60 MPa, and elongation at break from 8 to 16%. Crystallized
bio-based thermoplastic poly(oxamide urea)s with excellent thermal
and mechanical properties were successfully synthesized through a
nonisocyanate route.
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