Identification and Measurement of Intermolecular Interaction in Polyester/Polystyrene Blends by FTIR-Photoacoustic Spectrometry

Fourier transform infrared photoacoustic spectrometry was used to reveal and identify n-pi type intermolecular interaction formed in plastic comprising binary blends of polystyrene and a biodegradable polymer, either polylactic acid, polycaprolactone or poly(tetramethyleneadipate-co-terephthalate). This was the first reported direct and definitive experimental evidence of n-pi type bond formation in thermoplastic blends of these polyesters with polystyrene. Also, an infrared method was devised that permits quantitative measurement of the degree of interaction between the two polymers at various concentrations in the blends. The method employs spectral deconvolution by least squares curve fitting of the polymer carbonyl band into its underlying peaks. In a new algorithm the method compares deconvoluted Gaussian/Lorentzian peaks of the polymer blends with deconvoluted peaks in the neat polymers and computes both the magnitude and direction of change in the n-pi bond formation with change in polymer concentration. The results indicated that the degree of interaction was dependent on the type and concentration of the biodegradable polymer in the blend. These findings are supported by differential scanning calorimetry and thermogravimetric analyses. Unlike conventional spectral deconvolution methods, this technique with its new algorithm approximates infrared absorptivities of all the underlying peaks, and is thus a superior method that should be applicable to multicomponent polymer blends in general.