Structure and morphology of polyamide 66 and oligomeric phenolic resin blends: Molecular modeling and experimental investigations

Interaction between polyamide 66 (PA66) and phenol formaldehyde resin (PFR) was studied by molecular modeling for oligomeric model compounds and by experimental methods. Complexation between N-methylacetamide (NMA) and phenol was analyzed by calculating the equilibrium structure, hydrogen bond length, and interaction energy. Additionally, electrostatic potential (ESP) derived atomic charges were computed. Quantum mechanical calculations combined with an experimental Fourier transform infrared spectroscopy (FTIR) study revealed that there exists a strong hydrogen bonding between the carbonyl group of NMA and the hydroxyl group of phenol. Furthermore, the interaction energy of the NMA-phenol complex was found to exceed that of the NMA and phenol dimers and also their complexes with water molecules, which provides an explanation for the decreased water absorption of polyamides upon blending with PFR. FTIR and differential scanning calorimetry (DSC) studies of PA66-PFR blends demonstrated, in addition, miscible blends with hydrogen bond connections between the components. Furthermore, microscopic analyses by optical polarization microscope and transmission electron microscope (TEM) revealed that PFR induced spherulite growth in PA66.