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 associa tion of carboxylate (COONa) or acidic (COOH) groups into clusters. The se groups appear in the polymer due to the hydrolysis of nitrile group s. Clustering of hydrophilic acidic or salt groups occurs because of t heir thermodynamical incompatibility with the hydrophobic polymer back bone. 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 v isible 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 insta bility is related to the disintegration of clusters due to the solvati ng effect of water. The absorption background in the IR spectrum of a bleached sample also disappears.