Solid-state polymerization behavior of 1,3-bis(3-quinolyl)-1,4-butadiyne

1,4-Bis(3-quinolyl)-1,3-butadiyne (DQ) is known to be polymerized in solid state to give the corresponding polydiacetylene. However, the polymer yield of DQ bulk crystals is low. Thus, we prepared several types of DQ crystals by different procedures to find the reason for the low polymer yield. We found three modifications of DQ crystals and they were evaluated by spectroscopic measurements and X-ray diffraction. DQ bulk crystals (Crystal I) and thermally grown DQ crystals on Crystal I (Crystal II) have the same structure classified to Type A, which gives regular polydiacetylene structure in low polymer yields. DQ crystals grown on glass plates by sublimation (Crystal III) belong to the second modification of Type B. DQ nanocrystals prepared by the reprecipitation method (Crystal IV) are Type B, and thermally grown DQ crystals on nanocrystals (Crystal V) are Type C. Crystals of Types B and C could be polymerized in low yields without showing excitonic absorption of polydiacetylene indicating irregular polymerization other than 1,4-addition. For crystals of Type A, we found that the 1,4-addition polymerization proceeded only in near-surface portions of the crystals. It can be plausibly explained that mobile monomers in the near-surface portion are only able to take part in their polymerization, resulting in low polymer conversion.