Structure-property relationships of diacetylenes and their polymers

Structure-property relationships based on color changes are derived for diacetylenes, Y-(CH2)1-4-C ═ C─C ═ C-(CH2)1-4-Y and their polymers. The color of partially polymerized diacetylenes (PPD) and polydiacetylenes is determined by the number of methylene groups (MGs) adjacent to the unsaturated bonds. Most PPDs having 1 and 2 MGs are red while those having 3 and 4 MGs are blue. Upon extraction of unreacted monomer from PPDs, those having 4 MGs undergo an irreversible blue-to-red color transition while those having 1,2, and 3 MGs show little color change. Solutions of polydiacetylenes having 1,2, and 4 MGs undergo yellow → red color transitions while those having 3 MGs undergo a yellow → blue color transition upon addition of a nonsolvent. Several other properties such as melting and crystallization of polydiacetylenes are correlated with MGs.