Dimeric acid (DA) is a biobased derivative of plant oil.
Its polyamides
are usually weak polymers with a low melting point. In this work,
an efficient strategy was developed to enhance the thermal and mechanical
properties of DA polyamides (DAPAs). Two H2N-terminated
DAPA prepolymers (DAPAhs and DAPAddas) were synthesized through melt
polycondensation of dimeric acid with hexanediamine and decanediamine
(DDA), respectively. Diethyl oxalate was used as a chain extender
to increase the molecular weight, and modified DAPAs (DAPAhs-DEO and
DAPAddas-DEO) were obtained. Short and easy crystallizable oxamide
hard segments effectively improved the mechanical properties, crystallization,
and hydrophobicity of the DAPAs. The biobased modified DAPAs exhibited
good tensile strength up to 27 MPa, T
m between 105 and 151 °C, and water contact angles from 84 to
98°. Compared to DAPAhs-DEO, DAPAddas-DEO exhibited better comprehensive
mechanical properties because longer DDA segments made the oxamide
segments far from bulky DA segments and the oxamide segments in adjacent
main chains approached easier. Different from brittle 65DAPAh, 65DAPAh-DEO,
65DAPAdda, and 65DAPAdda-DEO showed good peel strength on the aramid
fabric. A simple and efficient method was established to prepare biobased
DAPAs with excellent properties.