Efficient Strategy\nto Enhance the Properties of Fully\nBiobased Linear Dimeric Acid Polyamides

Dimeric acid (DA) is a biobased derivative of plant oil.\nIts polyamides\nare usually weak polymers with a low melting point. In this work,\nan efficient strategy was developed to enhance the thermal and mechanical\nproperties of DA polyamides (DAPAs). Two H<sub>2</sub>N-terminated\nDAPA prepolymers (DAPAhs and DAPAddas) were synthesized through melt\npolycondensation of dimeric acid with hexanediamine and decanediamine\n(DDA), respectively. Diethyl oxalate was used as a chain extender\nto increase the molecular weight, and modified DAPAs (DAPAhs-DEO and\nDAPAddas-DEO) were obtained. Short and easy crystallizable oxamide\nhard segments effectively improved the mechanical properties, crystallization,\nand hydrophobicity of the DAPAs. The biobased modified DAPAs exhibited\ngood tensile strength up to 27 MPa, <i>T</i><sub>m</sub> between 105 and 151 °C, and water contact angles from 84 to\n98°. Compared to DAPAhs-DEO, DAPAddas-DEO exhibited better comprehensive\nmechanical properties because longer DDA segments made the oxamide\nsegments far from bulky DA segments and the oxamide segments in adjacent\nmain chains approached easier. Different from brittle 65DAPAh, 65DAPAh-DEO,\n65DAPAdda, and 65DAPAdda-DEO showed good peel strength on the aramid\nfabric. A simple and efficient method was established to prepare biobased\nDAPAs with excellent properties.