Photocycloaddition of Aromatic Bithiomaleimides: A Polymerization Strategy for Constructing Recyclable, Programmable, and Rigid Polyimide Backbones

Rigid polyimide specialty plastics combine excellent thermal, mechanical, and chemical resistance, but the stability of the imide group makes closed-loop recycling difficult. Here, we report a strategy for constructing rigid polyimide backbones through solution-state, UV-driven [2 + 2] cycloaddition polymerization of N -aromatic bithiomaleimides. The resulting polymers can be depolymerized thermally to enable closed-loop recycling. Photophysical studies and photopolymerization kinetics have confirmed that only bithiomaleimides containing a diphenyl sulfone linker can be used to construct rigid Poly(S-BMS). The platform was further programmed through side-chain engineering, and the mild photopolymerization conditions showed broad compatibility with functional groups. A series of functionalized polymers were prepared by one-pot copolymerization. In particular, BMSPB-85-C-7.5-F-7.5 combined high tensile strength (57.1 MPa) with a low dielectric constant ( k = 2.25 at 1 GHz), demonstrating the tunability of the Poly(S-BMS) system. Using dense hydrogen-bond engineering, we also designed Poly(S-BMSC), a recyclable polyimide adhesive based on this platform. Poly(S-BMSC) exhibited strong bonding to aluminum (LSS = 1.30 MPa) and copper (LSS = 1.21 MPa) substrates. Importantly, Poly(S-BMS) showed thermal reversibility, with more than 88% monomer recovery within 4 h at 160 °C and efficient cycling over at least five cycles. These findings support Poly(S-BMS) as a promising molecular platform for recyclable polyimides with potential utility as low-dielectric layers in flexible circuits and temporary bonding materials in semiconductor processing.