Coatings of PDMS-modified epoxy via urethane linkage: Segmental correlation length, phase morphology, thermomechanical and surface behavior

Modification of an aliphatic epoxy resin with silicone was carried out through urethane route. Hydroxy-terminated polydimethylsiloxane (HTPDMS) was reacted with toluene diisocyanate to form an isocyanate-capped prepolymer. The –NCO group of the prepolymer was further reacted with –OH group of an aliphatic epoxy adipate resin, obtained by reaction of adipic acid with an epoxy resin, to obtain silicone-modified epoxy resin. Silicone-modified epoxy resins containing 15 and 30 wt% of silicone prepolymer have been synthesized by this procedure. TGA analysis of the silicone-modified epoxy resin showed considerable improvement in thermal stability over the unmodified epoxy resin. Modulated differential scanning calorimetry (MDSC) was used to find the segmental correlation length of the silicone-modified polymers. The cured films of silicone-modified resins showed biphasic morphology as evidenced from scanning electron microscopy. Further, the thermomechanical property of the samples was investigated by dynamic mechanical analysis. The surface properties of the silicone-modified matrices were studied by atomic force microscopy and contact angle goniometry. The silicone-modified samples showed considerably lower surface energy, surface roughness and contact angle hysteresis compared to the unmodified resins.