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Crystal Structures and Topochemical Polymerizations of 7,7,8,8-Tetrakis(alkoxycarbonyl)quinodimethanes

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posted on 25.02.2004, 00:00 by Shinji Nomura, Takahito Itoh, Hirofumi Nakasho, Takahiro Uno, Masataka Kubo, Kazuki Sada, Katsunari Inoue, Mikiji Miyata
Highly conjugated monomers, 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes (methoxy (1a), ethoxy (1b), isopropoxy (1c), benzyloxy (1d), chloroethoxy (1e), and bromoethoxy (1f)), were synthesized. Recrystallizations of 1a, 1c, 1e, and 1f yielded two crystal forms (prisms (1aA) and needles (1aB), needles (1cA) and plates (1cB), prisms (1eA) and plates (1eB), and prisms (1fA) and needles (1fB)), which have different molecular packing modes by X-ray crystal structure analysis, indicating that the crystals are polymorphic. In the photopolymerizations of these monomer crystals in the solid state, 1aA, 1eA, and 1fA polymerized topochemically to give crystalline polymers. For their thermal polymerizations in the solid state, in addition to 1aA, 1eA, and 1fA, 1eB and 1fB polymerized, but polymers formed from the 1eB and 1fB were amorphous. The packing of quinodimethane molecules in the crystals was defined by four kinds of parameters, stacking distance (ds), the distance between the reacting exomethylene carbon atoms (dcc), the angles formed between the stacking axis and longer axis of the monomer molecule (θ1), and the shorter axis of the monomer molecule (θ2), and then the polymerization reactivity of these quinodimethanes in the solid state was discussed on the basis of these parameters.