Thiol-yne and amino-yne click polymerizations advance step-growth polymerization toward sustainable and photodegradable polymers

Conventional step-growth polymerization (SGP) faces stringent stoichiometric constraints and requires high conversion efficiency, thereby limiting precise control of molecular weight and polydispersity. This review critically evaluates the evolution of SGP from traditional constraints to precision-synthetic methodologies, with an emphasis on click chemistry-based approaches. We systematically compare CuAAC, thiol–yne, and amino–yne click polymerizations, analyzing their mechanisms, regioselectivity, kinetics, and applicability, along with RAFT copolymers and photodegradable polyketones. Metal-free thiol–yne and amino–yne polymerizations enable catalyst-free, room-temperature synthesis with > 95% conversion and up to > 95% trans selectivity. Precision polyketones from ADMET copolymerization (52 ketones per 1000 methylene units) degrade under UV irradiation (≥ 300 W m − 2 ), with degradation half-lives of 7–20 days under accelerated conditions, achieving tunable T g from − 20 °C to 150 °C. Click-SGP enables functional, on-demand degradable polymers for sustainable green plastics and biomedical applications, addressing essential environmental concerns. However, claims of “microplastic-free” degradation require qualification: complete backbone scission occurs under controlled accelerated UV conditions (I ≥ 300 W m − 2 , T ≥ 15 °C, aerobic), whereas natural weathering (10–50 W m − 2 ) results in slower, potentially incomplete degradation that may produce fragments requiring further environmental assessment.