In Situ Visualization of Microphase Separation in High-Performance Hyperbranched Polyurethane

Developing high-performance polyurethane (PU) elastomers requires overcoming the inherent trade-off between strength and toughness through precise control of the microphase separation morphology. Advances in nanostructure control and nondestructive microstructural detection are therefore essential. Herein, we report a hyperbranched PU elastomer (PU-HPAE x ) synthesized using hyperbranched poly(amino ester) (HPAE) as a dual-function macromonomer that acts simultaneously as a chain extender and a nonconventional fluorescent probe. The hyperbranched architecture creates a three-dimensional network enriched with high-density sacrificial hydrogen bonds (H-bonds) and a well-defined microphase-separated morphology, resulting in exceptional strength (65.80 MPa), elongation (1031.70%), and toughness (185.3 MJ m –3 )─overcoming classical strength–toughness conflicts. In addition, the hyperbranched topology promotes efficient cluster-triggered emission (CTE) via through-space conjugation (TSC), endowing PU-HPAE x with exceptionally strong fluorescence (quantum yield 11.16%). Critically, HPAE serves as an intrinsic fluorescent probe, enabling in situ visualization of micrometer-scale phase separation and its dynamic evolution, thereby providing key insights into the morphology–performance relationship. Furthermore, HPAE exhibits stimuli-responsive fluorescence under both mechanical strain and humidity, highlighting its potential application in smart sensing. By leveraging topological structure regulation, this work successfully establishes a novel strategy for fluorescent PU elastomers that integrates high performance with nondestructive visualization of microphase morphology.