Two-Dimensional Infrared 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)

Abstract

Infrared spectra have been measured for the cast films of 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 IR spectra have been divided into two sets for the 2D correlation: set S of high PS content (PS/PPE = 100/0, 90/10, 70/30) and set E of high PPE contents (PS/PPE = 50/50, 30/70, 10/90). The 2D synchronous correlation analysis in the CH stretching region of 3130−2810 cm-1 discriminates between the bands of PS and those of PPE. The 2D asynchronous correlation analysis identifies band variations that may be involved in the miscible blend formation. The specific interaction between PS and PPE in the blends is reflected in the frequency shift of the aryl CH “in-phase” out-of-plane wagging modes of PS and PPE, as well as in the intensity change of the “ring bands” of PPE and PS and of the methyl band of PPE. Thus, not only the aromatic rings of PS and PPE but also the CH3 groups of PPE seem to play important roles in the formation of the miscible blends. The optimal packing between PS and PPE requires that the PPE chains adopt the conformation A or B (marked by the asymmetric ether stretching bands at 1187 and 1176 cm-1, respectively), and the PS chains exist in a highly ordered state (marked by the CH2 asymmetric stretching band at 2909 cm-1). This paper demonstrates the usefulness of 2D IR spectroscopy for exploring the intermolecular interactions other than hydrogen bonding in polymer blends.