Synthesis, Crystal Structures, and Solid-State Polymerization of 8-[4-(Dimethylamino)phenyl]octa-5,7-diynyl Carbamates

Abstract

Six butadiyne monomers with (dimethylamino)phenyl and N-substituted urethane substituents were synthesized and their crystal structures and solid-state polymerization were investigated. In five of the six monomers, directions of the butadiyne stacking and the intermolecular hydrogen bonding between urethane groups coincided, and translational distance d between adjacent butadiyne moieties was around 5 Å. Among them, four monomers showed angle θ between the translation axis of the monomers and the butadiyne moiety of around 45°, which is appropriated for regular 1,4-addition polymerization. These geometries resulted in formation of polydiacetylenes with characteristic excitonic absorption and relatively high conversion. One monomer was found to have large θ, and the regular polymerization was not recognized to be quite low conversion. However, in the remaining one monomer among six, the directions of butadiyne stacking and intermolecular hydrogen bonding were different and d was much longer than 5 Å. However, distance between reacting carbons for 1,4-addition was short enough resulting in comparable conversion without regular polymerization. Although introduction of urethane group is effective to increase probability of the solid-state polymerization of butadiynes, hydrogen bonding direction, methylene chain conformation, and disorder of the aromatic rings were found to afford the variation from the appropriate conditions.