Heat-Resistant Strong Adhesive Consisting of Aromatic Polyamide With an Acid-Removable N-Protecting Group and a Thermal Acid Generator

Abstract

We present a heat-resistant strong adhesive system consisting of aromatic polyamide substituted with N-tert-butoxycarbonyl (Boc) groups, synthesized by polycondensation of bis(4-Boc-aminophenyl) ether (1) and isophthaloyl chloride (2), together with a thermal acid generator (TAG). Upon heating, the Boc groups are readily removed by the TAG-generated acid, affording N-H polyamide. Adhesion was conducted at 150°C or 250°C under a pressure of 10 kgf/cm² for 7 h to eliminate voids due to Boc-derived gaseous CO₂ and isobutene. For metal adherends treated at 150°C, the adhesion strength was 2–3 MPa. However, upon treatment at 250°C, above the T _g of N-H polyamide (236°C), the adhesion strength reached 7.43–6.25 MPa for sandblasted steel plate, cold commercial (SPCC) and stainless steel. Next, we prepared copolyamides with lower T _g values from 1, bis(4-methylaminophenyl) ether (3), and 2. Upon treatment at 150°C, the adhesion strength of SPCC with copolyamide consisting of 30% 1 and 70% 3 reached 6.83 MPa. As regards heat resistance, SPCC treated with N-Boc polyamide/TAG at 250°C maintained an adhesion strength of 7.0–7.5 MPa from room temperature to 250°C, whereas SPCC treated with copolyamide/TAG at 150°C maintained an adhesion strength of 6.8–8.2 MPa up to 200°C.