PMAN coloration due to carboxylate and acidic group clustering on alkali and thermal treatment

A new mechanism of polymethacrylonitrile (PMAN) coloration on thermal and alkali treatment is proposed. Coloration arises due to the association of carboxylate (COONa) or acidic (COOH) groups into clusters. These groups appear in the polymer due to the hydrolysis of nitrile groups. Clustering of hydrophilic acidic or salt groups occurs because of their thermodynamical incompatibility with the hydrophobic polymer backbone. Close contact of carboxyls in a cluster leads to the;overlap of their pi-electron clouds and a shift of their absorption band to the visible spectral region. In the infrared (IR) region, the clustering of acidic groups results in a broad background in a region below 3000 cm(-1) characteristic of systems with strong hydrogen bonds. Color instability is related to the disintegration of clusters due to the solvating effect of water. The absorption background in the IR spectrum of a bleached sample also disappears.