In situ cyclization reactions during the preparation of high-performance methacrylic acid/acrylonitrile/acrylamide ternary copolymer foam

A new high-performance methacrylic acid/acrylonitrile/acrylamide ternary copolymer foam was prepared by radical bulk copolymerization, and the reaction mechanism of in situ cyclization taking place during copolymer foaming as well as the heat treatment was examined too. Then, the crucial mechanism was validated via optical microscopy, infrared absorption spectroscopy (Fourier transform infrared), differential thermal analysis (differential scanning calorimetry), and thermogravimetric analysis. The results showed a weak exothermic peak at 149.17 degrees C and a strong endothermic peak at 270.85 degrees C in differential scanning calorimetry curves of the methacrylic acid/acrylonitrile/acrylamide copolymer after the foaming and heat treatment at 160 degrees C for 2 h and at 200 degrees C for 2 h. The peak temperature of the differential thermogravimetry curve was 175.87 degrees C, whereas the weight-loss rate was less at 276.58 degrees C in the thermogravimetry curves. In the case of the Fourier transform infrared curves, the -OH absorption peak at 930-970 and 1480 cm(-1) weakened, and the C-N absorption peak of the imide increased. The >C=O absorption peak at 1700 cm-1 occurred as an excursion phenomenon toward the low-frequency field; at the same time, the second absorption peak increased. Furthermore, the -C-N absorption peak at 2240 cm(-1) weakened, and a new -C=Nabsorption band appeared. All these data revealed that in situ cyclizations had taken place in the copolymer molecule chains, so some rigid ring structures appeared in the copolymer molecule chains, such as six-membered imide rings and ladder polymer structures. (C) 2007 Wiley Periodicals, Inc.