Debonding on Demand with Highly Cross-Linked Photopolymers: A Combination of Network Regulation and Thermally Induced Gas Formation

Photopolymerizable glues and cements that offer debonding on demand (DoD) through an external stimulus are of great interest for the fields of recycling and repair. State-of-the-art DoD solutions often require a high-energy impulse (e.g., >200 °C, strong force), which is due to the typical glassy nature of such photopolymer networks. Herein, various blocked isocyanates (BICs) that enable thermally induced gas formation at temperatures far below 200 °C are studied. Thermally induced gas bubble formation is accomplished within a linear, thermoplastic poly­(N-acryloyl­morpholine) matrix above glass transition temperature, introducing porosity. The resulting porosity within the material then causes mechanical failure. However, highly cross-linked photopolymer networks remain unchanged due to their glassy nature at temperatures well above 150 °C. A BIC-based thermolabile photopolymerizable cross-linker is prepared in order to create a polymer network with cleavable cross-link. Additionally, a β-allyl sulfone-based chain transfer reagent is used to tune the final cross-linking density and thermomechanical properties of the material. Above the resulting sharp glass transition (>60 °C), plastic deformation becomes possible, thus allowing formation of porosity. This introduces a covalently cross-linked, thermolabile photopolymer with a tailored network architecture as potential glue for DoD at ∼150 °C.