Three hexayne derivatives with different end groups-that is, 10,12,14,16,18,20-triacontahexayne-1,30-diol (1) and its diphenylurethane (2) and diphenylester (3)-were synthesized, and their solid-state polymerization behaviors were investigated. All three monomers were thermally polymerizable. Polymers from 1 and 2 showed an absorption maximum at about 730 nm, indicating that linear polydiacetylenes (PDAs) with octatetraynyl substituents were synthesized. However, broad absorption bands in the near-infrared region were only observed for 2 at 980 and 860 nm, indicating that regular polymerization occurred in 2 to give ladder-type PDA. On the other hand, a polymer from 3 showed a visible absorption increase but no clear absorption maximum. It was estimated that intermolecular hydrogen bonding between hexayne monomers helps to form polymerizable stacks in 1 and 2. In particular, urethane groups are more effective, and 2 showed the highest reactivity in this study with an ordered interlayer structure even after a two-step solid-state polymerization to give ladder-type PDA. Keywords: ladder polymer; polydiacetylene; solid-state polymerization; p-conjugated polymer Some butadiyne compounds are polymerized in the solid state by ultraviolet irradiation or by thermal treatment. This solid-state polymerization was clarified by Wegner 1 as a single-crystal-to-singlecrystal topochemical transition to yield polydiacetylene (PDA), which is classified as a one-dimensional p-conjugated polymer. Since the reaction is topochemically controlled, the reactivity of butadiyne monomers is greatly affected by their packing in crystals. 2 In fact, when the butadiyne monomers in crystals have a stacking distance d of about 5 Å between adjacent molecules in the array and an angle y of about 45 1 between the butadiyne rod and stacking axis, 1,4-addition polymerization occurs. Since molecular packing in crystals is determined by the intermolecular interactions between monomers, the selection of substituents attached to the butadiyne moiety is quite important in the preparation of PDAs. On the other hand, much research on the physical properties of PDAs, such as electrical, 3,4 chromic 5-7 and nonlinear optical (NLO) [8][9][10] properties, which originate from the p-conjugated backbone structure, have been undertaken. In particular, the third-order NLO properties of PDAs have attracted interest. To achieve larger NLO susceptibility (w (3) ) in PDA, it is necessary to increase the density of the p-conjugated polymer backbone and the p-electron number in a repeating unit. In this connection, we have synthesized ladder-type PDAs, in which two polymer backbones were introduced in a repeating unit. 11,12 In addition, several PDAs with p-conjugated substituents, such as aromatic rings and C-C multiple bonds, directly bound to the polymer backbone [13][14][15][16][17][18][19][20][21][22] have been synthesized to obtain PDAs with absorption maxima at longer wavelengths, resulting in larger w (3) -values. In particular, oligoyne derivatives with five...
