Synthesis of Heat‐resistant Polymers by Thiol–Ene Reaction of N‐Allylmaleimide Copolymers Using Glycoluril Crosslinkers with Rigid Molecular Structures

Abstract

ABSTRACTWe carried out the thermal curing of the copolymers of N‐allylmaleimide (AMI) and 2‐ethylhexyl acrylate (2EHA) using 1,3,4,6‐tetra(2‐mercaproethyl)glycoluril (G1), 1,3,4,6‐tetra(3‐mercaptopropyl)glycoluril (G2), 1,3,4,6‐tetraallylglycoluril (G3), triallylisocyanurate (TAIC), and pentaerythritol tetrakis(3‐mercaptobutyrate) (PEMB) as the crosslinkers. Based on the results for the analysis of thiol–ene reactions monitored by IR spectroscopy, it was confirmed that the curing rate significantly depended on the combination of the used crosslinkers. The insoluble fraction after curing was more than 90% for the systems using the glycoluril crosslinkers, while the conversion of the allyl groups was suppressed due to the rigid structure of these crosslinkers. The heat resistance and the mechanical properties of the crosslinked polymers were investigated by thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, and mechanical tensile tests. For the products cured using the glycoluril crosslinkers, the glass transition temperature (Tg) and the maximum temperature of thermal decomposition (Tmax) were 54–59 °C and 395–409 °C, respectively, being higher than those for the cured product prepared with PEMB and TAIC as the conventional crosslinkers. The elasticity (75–139 MPa), the maximum strength (3.0–4.1 MPa), and the adhesion strength (6.7–10.7 MPa) for the polymers cured with the glycoluril crosslinkers, determined by the mechanical tensile and single lap‐shear adhesion tests, were higher than those for cured materials produced with PEMB. Thus, the thermal and mechanical properties of the maleimide copolymers were efficiently enhanced by crosslinking using the rigid glycoluril compounds. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 923–931