THERMO-CHEMICAL REACTIONS AND STRUCTURAL EVOLUTION OF ACRYLAMIDE-MODIFIED POLYACRYLONITRILE

• Published in: Chinese journal of polymer science Vol. 28; no. 3; pp. 367 - 376
• Main Authors: Wu, Xue-ping, Zhang, Xian-long, Lu, Chun-xiang, Ling, Li-cheng
• Format: Journal Article
• Language: English
• Published: Heidelberg Chinese Chemical Society and Institute of Chemistry, CAS 01.05.2010; Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China%School of Chemical Engineering, Hefei University of Technology, Hefei 230009, China%College of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China
• Subjects: Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Industrial Chemistry/Chemical Engineering; Polymer Sciences; 丙烯酰胺; 共聚物; 原位红外光谱; 构造演化; 热化学反应; 空气流动; 聚丙烯腈; Thermal properties; Carbon fibers; Cyclization mechanism; Activation energy; Acrylonitrile-acrylamide copolymers
• DOI: 10.1007/s10118-010-9026-9
• ISSN: 0256-7679

Thermal properties of acrylonitrile （AN）-acrylamide （AM） copolymers for carbon fibers were studied by DSC and in situ FTIR techniques in nitrogen （N2） and air flows. The cyclization mechanism and stabilization behavior of polyacrylonitrile （PAN） were discussed. In N2 flow, it was found that AM had the ability to initiate and accelerate cyclization process, which was confirmed by the fact that the initiation of nitriles shifted to a lower temperature. Compared to AN homopolymer, the initiation temperature of cyclization was ahead 32 K by introducing 3.59 mol% AM into the copolymer. The exothermic reaction was relaxed due to the presence of two separated exothermic peaks. Accompanied by DSC, in situ FTIR and calculation of activation energy, the two peaks were proved to be caused by ionic cyclization and free radical cyclization, respectively, and the corresponding cyclization mechanism was proposed. With increasing in AM content, the ionic cyclization tends to be dominant and the total heat liberated first increases and then decreases. For AN homopolymer, the activation energy of cyclization is 179 kJ/mol. For AN-AM copolymer （containing 3.59 mol% AM）, the activation energy of ionic cyclization is 96 kJ/mol and that of free radical cyclization is 338 kJ/mol. In air flow, similar cyclization routes occur and the difference is the contribution of oxidation. The oxygen in environment has no remarkable effect on cyclization of AN homopolymer but retards the cyclization of AN-AM copolymers. For AN-AM copolymer with 3.59 mol% AM, the cyclization temperature is postponed 10℃ in air.