Mechanical and thermal studies of intercross-linked networks based on siliconized polyurethane-epoxy/unsaturated polyester coatings

Two different intercross-linked networks (ICN) of siliconized polyurethane-epoxy/unsaturated polyester (UP) coatings were developed. Epoxy and UP resins were modified with polyurethane (PU) prepolymer and hydroxyl terminated polydimethylsiloxane (HTPDMS) using -gamma-aminopropyl triethoxysilane (gamma-APS) and vinyltriethoxysilane (VTES) as silane cross-linkers and dibutyltindilaurate (DBTL) as catalyst. Aromatic polyarnine adduct (A) and aliphatic amine (B) were used as curatives; for epoxy and methyl isobutyl ketone peroxide (C) as curative for UP resin. The coating materials were obtained in the form of tough films and characterized for their mechanical properties such as tensile strength and impact test as per ASTM methods. The thermal stability of the ICN coatings was studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) and compared with unmodified epoxy/UP systems. Mechanical properties were enhanced with incorporation of PU (10 wt. %) and silicone (10 wt. %) due to the toughening of brittle epoxy and UP systems. The introduction of PU into unmodified epoxy/UP coating systems reduces the thermal stability due to the presence of thermally weak urethane linkages whereas, the incorporation of 10 wt.% silicone into PU modified epoxy/UP systems improves their thermal stability due to the partial ionic nature, high bond energy and thermal stability of -Si-O-Si- linkage. (C) 2003 Elsevier B.V. All rights reserved.