Homogeneous nucleation in polyamide 66, a two-stage process as revealed by combined nanocalorimetry and IR spectroscopy

Abstract Nanocalorimetry and Fourier transform infrared (FTIR) spectroscopy are combined to measure the calorimetric properties molecular spectra of same sample (sample amount about 5 ng) polyamide 66 (PA66). By determining IR difference absorption between a quenched annealed at varying temperatures ( T ) annealing time t ), initial steps homogeneous nucleation is for first revealed on scale, long before crystallization takes place. As starting point (i), isolated H-bonds formed (N–H) (C = O) moieties adjacent (neighboring) polymer segments promoted by far-reaching dipole–dipole interactions. In second step (ii), realign, which in part requires opening already established H-bonds. stage FTIR intensity free f decreases while that H-bonded b ones increases as function constant . This implies an increase H-bonding network amorphous domains. The studied PA66 characterized number corresponding decrease transitions ordered crystalline structure. attributed change from γ α polymorphs PA66. non-polar methylene units largely unaffected during steps, where no changes overall heat capacity detectable, proving these occur prior onset crystal growth. Graphical abstract