Near-infrared spectroscopy of polymer blends

Date of Completion

January 1996


Chemistry, Analytical|Chemistry, Physical|Chemistry, Polymer




Near-infrared spectroscopy was used to study the nature of specific interactions and its effect on the miscibility of the metal salts of sulfonated polystyrene (M-SPS) with polyamide 6 (PA-6). The molecular origin of various N-H overtone bands in the near-infrared (NIR) region was addressed. Peaks in the absorption spectra that are due to the N-H stretch vibration are affected by changes in the local environment of the N-H group. These were assigned based on studies made using model compounds. Changing the composition of the blends or the counter ion of the SPS was found to affect the environment of the amide groups of the PA-6, and this was manifested in the NIR spectra of these blends.^ Miscibility of M-SPS/PA-6 blends was due to the formation of a specific complex between the metal ion and amide groups. Transition metal ions (Zn$\sp{2+}$ and Mn$\sp{2+}$) formed a metal-nitrogen ligand and lithium formed metal-oxygen ligand. The strength of the inter-polymer interactions for different metal cations decreased in the order: $\rm Mn\sp{2+}\ge Zn\sp{2+}>Li\sp{+}>K\sp{+}$. The miscibility of these blends was confirmed by the presence of a single, composition-dependent, glass transition temperature as measured using differential scanning calorimetry.^ The N-H groups exist in various molecular environments: as self-associated form in the crystalline and amorphous phases, as a complex with the metal ion, and in the unassociated form. NIR was used to determine the relative populations of the N-H groups in their respective molecular environments. The effect of temperature on the relative populations was also investigated.^ Blends of poly(e-caprolactone) (PCL) and poly(hydroxypropylether of bisphenol A) (Phenoxy) were also studied by NIR spectroscopy. Intermolecular interaction between the carbonyl and hydroxyl groups of the two polymers was investigated. Addition of PCL to the system shifted the position of the O-H stretch overtone band to higher frequency as a consequence of hydrogen bonding. On raising the temperature for these blends, the peak maxima of the O-H band shifted to higher frequency due to dissociation of the hydrogen bonded O-H groups to the free form. ^