A chemical bonding adhesive for PEEK based on aromatic ring interactions

Reliable bonding to polyetheretherketone (PEEK) remains challenging because of its semicrystalline, chemical-resistant nature. In this study, a two-part adhesive was developed for grit-blasted and otherwise not aggressively treated PEEK that targets the phenylene backbone units of PEEK through noncovalent π-π interactions and chain-level compatibility.

Miscibility of candidate solvents and monomers with PEEK powder was measured by differential scanning calorimetry (DSC) to identify chain-level effects. A formulation based on 1-vinylimidazole and glycidyl methacrylate, with 2-hydroxyethyl methacrylate, urethane dimethacrylate, camphorquinone/2-(dimethylamino)ethyl methacrylate, and p-methoxyphenol, was designed as a two-part system mixed 1:1 before use. Interfacial chemistry was examined by Fourier transform infrared spectroscopy (FTIR; KBr). Micro-shear bond strength was tested on grit-blasted PEEK at 24 h and 2 weeks and compared with a commercial CAD/CAM adhesive and a no adhesive control.

DSC of neat PEEK showed a small heat-flow feature near ∼80 °C. Several liquids modified this feature and the apparent heat capacity. FTIR after applying/curing the adhesive revealed decreased PEEK phenylene/ether bands and increased epoxy ring-opening product bands after 1 week. The best formulation (Adhesive No. 1) achieved a micro-shear bond strength of 19.3 ± 3.4 MPa at 2 weeks, significantly higher than the negative control and commercial adhesive.

Targeting PEEK's phenylene units through π-π interactions and chain-level compatibility produced strong bonding on PEEK without aggressive chemical pretreatments, suggesting a clinical route for adhesive dentistry involving PEEK that could be applied to other aromatic engineering polymers after further validation.