Debonding on Demand

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.

C. Gorsche, C. Schnöll, T. Koch, N. Moszner, R. Liska: "Debonding on Demand with Highly Cross-​Linked Photopolymers: A Combination of Network Regulation and Thermally Induced Gas Formation"; Macromolecules, 51 (2018), 3; S. 660 - 669.