Two-dimensional Fourier transform Raman correlation spectroscopy studies of polymer blends: Conformational changes and specific interactions in blends of atactic polystyrene and poly(2,6-dimethyl-1,4-phenylene ether)

Fourier transform (FT) Raman spectra have been measured for atactic polystyrene (PS), poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and their blends of different compositions: PS/PPE = 90/10, 70/30, 50/50, 30/70, 10/90. Composition-dependent spectral variations of the blends have been analyzed by generalized two-dimensional (2D) correlation spectroscopy to study the conformational changes and specific interactions in the blends. The FT-Raman spectra have been divided into two sets for the 2D correlation: set A of high PS contents (PS/PPE = 100/0, 90/10, 70/30) and set B of high PPE contents (PS/PPE = 50/50, 30/70; 10/90). The 2D synchronous correlation analysis discriminates between the bands of PS and those of PPE and detects bands that are not readily identifiable in the one-dimensional spectra of PS and PPE. The main chain conformation of PS undergoes a drastic change when mixed with PPE, as reflected in the abnormal behavior of bands at 1448 and 1329 cm(-1) due to the backbone methylene vibrations and of the band at 1070 cm(-1) due to the C-C stretching vibration. The 2D asynchronous correlation analysis reveals many out-of-phase band variations showing opposite trends in set A and set B. Bands at 1614, 1590, 1378, 1305, 1131, 1112, 1093, 1004, 572, and 241 cm(-1) due to PPE and those at 1602, 1031, 1000, and 202 cm(-1) due to PS are found to be indicative of the specific interaction common to set A and set B. It also reveals bands that are unique to the particular molecular interactions in set A or set B: 1606 cm(-1) for set A and 1309 cm(-1) for set B. It is concluded from the asynchronous spectra 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.