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 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 CH3 groups of PPE play important roles in the formation of the blends.