Topochemical polymerization using bis-thyminyl monomers†
Abstract
Topochemical polymerization is one way to synthesize novel macromolecular architectures with stereoregular chain structures. The [2π + 2π]-cycloaddition of certain conjugated diolefin monomers is one such form of topochemical polymerization. Unfortunately, the design of new monomers that can undergo topochemical [2π + 2π]-polymerization to form linear polymers can be a formidable challenge due to the strict geometrical criteria governing the reactivity of monomer crystals. In this research ten bis-thymine monomers were synthesized, that varied with respect to the N1-functionality, the size of the N3–N3-polymethylene spacer, or the type of rigid N3–N3-aryl spacer employed. On irradiation, five of the crystalline monomers were found to undergo topochemical photo-reactions. The crystal structures of the bis-thyminyl monomers were used to investigate the monomer structure–reactivity relationships. The molecular weights of the photo-products were determined and the thermal properties of some of the new materials were also evaluated using thermo analytical techniques.