Metal-free phenylpropiolate–azide polycycloaddition: efficient synthesis of functional poly(phenyltriazolylcarboxylate)s

Cu(I)-mediated and metal-free click polymerizations of azides and terminal alkynes have been developed into powerful techniques for constructing linear and hyperbranched polytriazoles. However, the 1,3-dipolar cycloaddition of azides with internal alkynes is rarely employed as a synthetic tool to prepare functional polymers. In this work, metal-free phenylpropiolate-azide polycycloaddition was developed for efficient synthesis of poly(phenyltriazolylcarboxylate)s (PPTCs), a kind of polyester. The aromatic and aliphatic diphenylpropiolates could readily react with diazides under heating, affording soluble PPTCs with high molecular weights (Mw up to 28 500) in excellent yields (up to 98%). The polymerization is insensitive towards oxygen and moisture, and can proceed smoothly in an open atmosphere. The obtained PPTCs are thermally stable with 5% weight loss temperatures higher than 318 °C. As the polymers contained ester groups, they exhibited fast degradation under basic conditions. The PPTC containing tetraphenylethene moieties shows a unique phenomenon of aggregation-induced emission, and can be employed as a fluorescent chemosensor to sensitively detect explosives. Its thin film can generate two-dimensional fluorescent photopatterns by UV irradiation.