Structural transformation polydiacetylene

The solid-state polymerization reaction of S2N2 is non-unique, which explains why (SN) bas much lower structural perfection than is obtainable for certain polydiacetylenes. In general terms, a solid-state transformation will be nonunique unless all symmetry elements of the monomer lattice are preserved in the product lattice. This means that a solid-state polymerization reaction will be nonunique unless (1) the monomer site symmetry is a possible... 

Until 2003 [11] no single crystal to single crystal transformation of a monosubstituted diacetylene to polydiacetylenes had been reported [27]. The Cambridge Structural Database contains only four entries for terminal diacetylenes and none of these have the supramolecular structural features necessary for a topochemical 1,4-polymerization as outlined in Scheme 5.1. There are many reasons for the lack of information on the topochemical polymerization of unsymmetrical monosubstituted diacetylenes. One is that the oxidative coupling procedure, readily applied for the preparation of symmetrical diacetylenes, is not easily applied to the preparation of unsymmetrical diacetylenes. Another factor is that unsymmetrical diacetylenes lack a center of symmetry and are less likely to pack with simple translational symmetry, a structural feature commonly observed for diacetylenes that undergo a topochemical polymerization (see Scheme 5.1). 

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