Pyrolysis-Derived Telechelic Polypropylene Enables Mechanochromic Mapping of Cavitation in Polyolefin Matrices

Abstract

Herein we present excimer-forming telechelic mechanophores derived from isotactic polypropylene (iPP) via controlled pyrolysis. This process yields oligomers bearing terminal vinylidene groups, which are subsequently functionalized with pyrene to produce a mechanochromic additive (iPP-Py) sensitive to mechanical deformation. By blending this material with diverse matrices —HDPE, LLDPE, POE, and PCL— stress redistribution, interfacial debonding, and cavitation are revealed through real-time fluorescence changes. The mechanochromic behavior of iPP-Py is strongly influenced by processing conditions: films prepared at 150 °C retain PP-rich domains with weak interfacial adhesion, which act as stress concentrators and are essential for activating the mechanophore. Matrix-dependent responses emerge upon deformation. LLDPE and PCL blends display excimer quenching upon stretching, while POE exhibits an unconventional increase in the 475 nm excimer band—an optical signature directly linked to cavitation. Microscopies confirm that void nucleation and growth around poorly compatibilized PP domains locally increase pyrene concentration, enhancing excimer formation and enabling visualization of cavity evolution. Quantum-chemical calculations support this mechanism by correlating excimer emission with local packing constraints. Overall, this study demonstrates that pyrolysis-derived iPP can serve as a platform for designing mechanochromic additives and provides a robust approach for probing deformation, interfacial failure, and cavitation in polymer blends. The present work represents a model study, and future investigations will extend this strategy to real recycled polyolefin systems.