Influence of the Bio-Based Epoxy Prepolymer Structure on Network Properties

Three different bio-based epoxy prepolymers are studied: one that is synthesized from isosorbide and two that are commercial prepolymers derived from sorbitol and cardanol. The chemical structures are analyzed by SEC, ESI-TOF MS, and FTIR analyses. The bio-based prepolymers exhibit different structures, either aromatic with long aliphatic chains for the epoxy prepolymer derived from cardanol (DGECAR), with high functionality for the sorbitol polyglycidyl ether (SPGE) or a short and cyclic structure for the epoxy prepolymer derived from isosorbide (DGEDAS(0)). A traditional petroleum-based epoxy prepolymer, diglycidyl ether of bisphenol A (DGEBA) is also used for comparison. Gelation and reactivity of the different precursors with an isophorone diamine hardener are studied using rheological measurements and differential scanning calorimetry. Glass transition temperatures of the epoxy networks are evaluated and the thermal stability is also studied by thermo-gravimetric analysis.