Catalyst-free Multicomponent Polymerization Based On Alkynes

Scientists have made efforts to combine multicomponent reactions(MCRs) which can afford single product from three or more starting materials in a one-pot procedure, with polymer chemistry for efficient synthesis of polymers with well-defined structure, large molecular weight, diverse functionalities, and practical applications. Multicomponent polymerization(MCP) is an emerging field of polymer science frontier, including the isocyanide-based MCP and alkyne-based MCP, etc. Through polymerizations of alkynes with rich chemical properties and high reactivity, functional polymers with unsaturated structures and optoelectronic properties can be obtained. However, most of the reported alkyne-based polymerizations involve metal catalysts, resulting in metallic residues in polymer products which may have a bad influence on the functionalities of the polymer materials such as photophysical properties, biocompatibility, and mechanical property.In order to solve the problem of residues of metal catalysts, we proposed a strategy of catalyst-free alkyne-based multicomponent polymerization in this thesis. Inspired by the efficient small molecular multicomponent reactions, through the design of proper monomer structures and the optimization of polymerization conditions such as solvent, concentration, temperature, time, etc, we have successfully developed two types of catalyst-free alkyne-based multicomponent polymerizations.Firstly, we developed a catalyst-free multicomponent polymerization of aromatic diynes, elemental sulfur, and aliphatic diamines as monomers to synthesize soluble polythioamides with high yield, large molecular weight, and well-defined structures in a one-pot polymerization. The elemental sulfur first reacts with aliphatic diamines to yield an active ammonium polysulfide chain intermediate, which further reacts with the diynes to afford polythioamides with 97% yield and molecular weights of up to 127 900 g/mol. Elemental sulfur was directly used as a feedstock in the polymerization to prepare sulfur-containing polymers with well-defined structure, good solubility, and high refractive indices. Interestingly, unexpected fluorescence is observed from the polythioamides, despite the absence of conjugated structures and typical fluorophores, owing to the ―heterodox clusters‖ comprised of a large number of lone pair electron-containing heteroatoms, which was formed through intrachain and intermolecular interactions such as hydrogen bonding and nâ†'?* interaction between thioamides.Through the combination of Petasis MCP and A3-coupling MCP, we have successfully introduced four components into a single polymerization. With the high reactivity of the activated phenylpropiolic acid, the catalyst-free multicomponent polymerization of aliphatic diamines, formaldehyde, diboronic acid, and phenylpropiolic acid was realized to afford poly(dipropargylamine)s in a one-pot procedure. The diamines and diboronic acid were first reacted with formaldehyde to yield an active secondary amine intermediate, which further reacts with phenylpropiolic acid and another molecule of formaldehyde in an A3-coupling reaction, affording polymers with molecular weight of up to 13 900 g/mol in 85% yield. The poly(dipropargylamine)s generally enjoy high refractive indices.The catalyst-free alkyne-based three-/four-component polymerizations reported in this thesis provide new polymer synthetic strategies with great simplicity and efficiency. Furthermore, they offer new convenient methods for the preparation of functional polymer materials with diverse structures.