Structure and properties of dimer acid-based polyamide nylon copolymer modified by adipic acid

The integrated properties of dimer acid-based polyamide nylon (DAPA) were improved with adipic acid embedded into the main chain of a series of DAPA copolymers by melt phase poly-condensation method. The effect of adipic acid on the state of aggregation, thermal, physical and mechanical properties of DAPA (dimer acid-based polyamide) was investigated by IR (infrared spectra), UV-Vis (UV-Vis spectra), DSC (differential scanning calorimeter) and TG (thermogravimetric analysis). The results show that addition of a small amount of adipic acid to DAPA increases the density, melting point, water absorption, and decreases the Izod notched impact strength, and deteriorates the thermal stability. However, a large amount of adipic acid causes a rapid decrease in the impact strength due to brittle-ductile transition. The presence of adipic acid leads to the change of phase structure from y to α, β crystal forms, and increases the content of α, β crystal phases. It can also reduces the energy of dissociation of the C-N bond, and modulates quantities of hydrogen bonds of intra and inter molecules, and delocalized direction and delocalized degree of σ-π* electrons, which favors the activation of the amide bond.