Metal-and Solvent-free, Clickable Synthesis And Postpolymerization Functionalization Of Poly(Triazole)s

Recently, the Cu(I)-catalyzed azide-alkyne cycloaddition reaction, dubbed “clickchemistry” by Sharpless and coworkers in2001, has attracted significant attention.This click reaction is featured with experimental simplicity, high efficiency,regioselectivity, atom economy, and tolerance to functional groups, which make itattractive for polymerization as well as for modification of macromolecule. Themetallic catalysts used in the Cu(I)-catalyzed click polymerization can formcomplexes with the triazole rings, which are difficult to remove from the products andare detrimental to the properties of polymers, thus limiting their applications. Anappealing solution is the development of catalyst-free click chemistry procedures.Therefore, metal-free, thermally initiated click polymerization has been developedthrough using more active monomers.In this study, we took an A2+B2approach for the synthesis of linearpoly(triazole)s (PTAs) by the metal-and solvent-free click polymerization. Themonomers methyl3,5-dipropargyloxylbenzoate and methyl3,5-bis(4-azidobutoxy)benzoate were prepared by etherification of methyl3,5-dihydroxybenzoate with propargyl bromide and1,4-dibromobutane followed bynucleophilic displacement of bromine with sodium azide. The progress ofpolymerization was monitored by1H NMR, FTIR, and GPC. In order to obtainwell-defined polymers, multi-step precipitation method was thus developed tofractionate polymer product by using different precipitating agents, yieldingwell-defined polymer fractions with low polymer polydispersity index (PDI <1.30).Furthermore, the methyl benzoate moieties in the main chain can serve as usefulbuilding blocks for further postpolymerization functionalization. The obtained PTAscan be further functionalized by sequential treatment with hydrazine hydrate, carbondisulphide, and hydrazine hydrate, resulting in the formation of4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol moieties.The postfunctionalization ofpolymer was confirmed using both FTIR and NMR spectroscopy. Thermal analysisshowed marked changes in glass transition temperature and thermal stability of thefunctionalized PTAs.