Influence of Octaglycidyl‐ POSS on Processing Behavior, Gelation Kinetics, and Thermomechanical Properties of a DGEBA /Polyamidoamine Epoxy System

Octaglycidyl polyhedral oligomeric silsesquioxane (OG‐POSS) was incorporated at 0, 1.5, 3.0, and 5.0 phr into a diglycidyl ether of bisphenol‐A (DGEBA) epoxy cured with a polyamidoamine (PAA) hardener to raise the thermal ceiling of flexible PAA networks without sacrificing liquid processing. Steady‐state rheometry showed a non‐monotonic effect on uncured viscosity: 1.5 and 3.0 phr reduced it by 17% and 15% (to 10.7 and 11.0 Pa s at 10 s −1 ), while 5.0 phr raised it by 43%; all formulations were essentially Newtonian in ascending sweeps, with mild descending‐ramp thixotropy. Gel time was likewise non‐monotonic: essentially unchanged at 1.5 and 5.0 phr but 18% shorter at 3.0 phr, where the processing window also contracted most. Dynamic mechanical analysis showed glass transition temperature ( T g ) rising up to 19°C at 1.5 phr (73°C–92°C), while the glassy storage modulus decreased 29%–34% and the apparent crosslink density increased non‐monotonically by 47%–71% at all three loadings. Both trends are consistent with the octafunctional Si 8 O 12 cage acting as a network junction that increases crosslink density, with the concurrent T g increase reflecting greater network constraint. Among the loadings studied, 1.5 phr OG‐POSS gave the most favorable balance of T g enhancement, uncured viscosity, and processing window.