Two-Dimensional Near-Infrared Correlation Spectroscopy Studies of Compatible Polymer Blends: Composition-Dependent Spectral Variations of Blends of Atactic Polystyrene and Poly(2,6-dimethyl-1,4-phenylene ether)

Generalized two-dimensional near-infrared (2D NIR) correlation spectroscopy has been applied to the study of the conformational changes and specific interactions in blends of atactic polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene ether) (PPE). NIR diffuse reflectance spectra have been measured for PS, PPE, and their blends of different compositions: PS/PPE = 90/10, 70/30, 50/50, 30/70, 10/90. The samples are divided into two sets for 2D correlation: set A with high PS content (PS/PPE = 100/0, 90/10, 70/30) and set B with high PPE content (PS/PPE = 50/50, 30/70, 10/90). The 2D synchronous correlation analysis separates the bands of PS from those of PPE. The 2D asynchronous correlation analysis produces cross-peaks that are indicative of the specific interaction or the conformational change in the blends. Two “blend bands” are identified at 8443 cm -1 (PPE) and 6887 cm -1 (PS), whose origin has been attributed to the molecular level changes induced by the formation of blends. It is found that the NIR region of 7700−6400 cm -1 is most suitable for 2D analysis of the specific interaction between PS and PPE, while the region of 5600−4900 cm -1 is best for 2D analysis of the conformational features common to both sets A and B, and the region of 4750−4300 cm -1 is best for conformational features unique to set A or B. It is concluded that not only the phenyl rings of PS and PPE but also the CH 3 groups of PPE play important roles in the formation of the blends.