Radiation Induced Solid-State Polymerization of Acetylenedicarboxylic Acid

Radiation induced solid-state polymerization of acetylenedicarboxylic acid was carried out at room temperature in open atmosphere and under vacuum conditions. The gray colored powder polymer obtained was insoluble in most common solvents but only partially soluble in DMSO and THF. The limiting conversion to polymer was about 5%. The polymer was characterized by IR, UV, DP-MS, DSC, TGA, and XRD. The mechanism of polymerization was elucidated from the available data. Polymerization followed a free radical mechanism. However, before the addition of monomer molecules to the growing chain, at least one of the carboxylic groups of the monomer breaks away as CO or CO2. The formation of side group cyclization takes place. At least one of the bonds in the side cyclic group is an etheric bond. The DSC, TGA, and XRD results showed that the polymer was partially crystalline and showed no melting up to 1200°C. The mechanism of polymerization and assigned chain structure was studied by the direct pyrolysis mass spectrometric method. The crystal structure of monomer and polymer was investigated by the XRD method. Both monomer and crystalline polymer were monoclinic with similar cell parameters. Thus, the polymerization follows a topotactic mechanism. The unpolymerized monomer retains its crystal structure and, therefore, CO or CO2 in the monomer molecule has to be eliminated before polymerization could take place.