Alternating partially quaternized polytriazole amphiphiles: bridging neutral and ionic domains for tunable aggregation

Poly(1,2,3-triazole)-based polymers remain underexplored as a versatile platform for biomedical soft materials. Here, we report the modular synthesis of amphiphilic poly(1,2,3-triazole)-<i>co</i>-polytriazolium <i>co</i>polymers (qH-PETH) <i>via</i> copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) polyaddition and post-polymerization quaternization with a degree of quaternization equal to (0.85). These polymers exhibit unusual visible colouration in the absence of chromophores-appearing almost colourless in <i>N</i>-methyl-2-pyrrolidone (NMP), orange in DMSO, and pale orange in water-accompanied by a pronounced red shift in non-polar solvents such as dichloromethane (DCM) or chloroform. This optical behaviour is attributed to solvent-dependent supramolecular aggregation. Dynamic light scattering (DLS) measurements reveal hydrodynamic diameters of <20 nm in water and approximately 500 nm in chloroform for quaternized polymers (qH-PETH), indicating strong aggregation in low-polarity environments. UV-vis spectroscopy and atomic force microscopy (AFM) further support aggregation-induced optical effects modulated by solvent polarity and hydrogen-bonding capacity. Both neutral and quaternized polymers display excellent cytocompatibility toward human cell lines (HeLa, HEK293, THP-1) at concentrations up to 100 μg mL^-1, with no detectable immunogenic activation. These findings position poly(1,2,3-triazole)-<i>co</i>-polytriazolium copolymers as a promising, tunable class of biocompatible soft materials for biointerface engineering and responsive biomedical applications.