Maleimide based Alder-ene thermosets: recent advances

High-performance polymer matrix composites, particularly for aerospace applications, are designed to withstand high thermal and aerodynamic stresses. Among the diverse thermoset resins, bismaleimide (BMI) resin stands out as a class of high-performance addition-curable polyimide resin having excellent thermal, physical, and thermomechanical properties. However, their inherent limitations including brittleness and poor processability are impediments for their wide acceptability, necessitating their structural modification, co-reaction, or blending with suitable compounds to obviate the shortcomings. The widely accepted strategies for structural modification of BMI for conferring low temperature cure characteristics and enhanced toughness is to react with allyl-functional compounds. The allyl compounds react with maleimide groups via the Alder-ene reaction. This article deals with the recent advances in this domain. It critically compiles the recent literature on the development of Alder-ene–type BMI polymers based on reaction of various maleimides with allylated compounds. The various systems, their synthesis strategies, curing, and related properties are discussed. Intersystem comparisons have also been made. Wherever relevant, the article also discusses the cure characteristics of Alder-ene polymerization and further modifications of these resins with high-performance thermosets and thermoplastics. Recent studies on nanomodification on the Alder-ene polymer network have also been reviewed. Other relevant developments in this domain like, click reaction-based self-healing BMI systems and BMI-based shape memory polymers are also discussed. It is concluded that this area is fast developing and is an active area of research with a potential for evolving as an advanced engineering plastic for applications ranging from adhesives to high-temperature and high performance structural composites for civil, defense, and aerospace applications