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 Tg 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 Tg 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.