Cage and linear structured polysiloxane/epoxy hybrids for coatings: Surface property and film permeability

Three polysiloxane/epoxy hybrids obtained by evolving cage- or linear-structured polysiloxane into poly glycidyl methacrylate (PGMA) matrix are compared used as coatings. One is the cage-structured hybrid of P(GMA/MA-POSS) copolymer obtained by GMA and methacrylisobutyl polyhedral oligomeric silsesquioxane (MA-POSS) via free radical polymerization, the other two are PGMA/NH₂-POSS and PGMA/NH₂-PDMS hybrids by cage-structured aminopropyllsobutyl POSS (NH₂-POSS) or linear-structured diamino terminated poly(dimethylsiloxane) (NH₂-PDMS) to cure PGMA. The effect of MA-POSS, NH₂-POSS and NH₂-PDMS on polysiloxane/epoxy hybrid films is characterized according to their surface morphology, transparency, permeability, adhesive strength and thermo-mechanical properties. Due to caged POSS tending to agglomerate onto the film surface, P(GMA/MA-POSS) and PGMA/NH₂-POSS films exhibit much more heterogeneous surfaces than PGMA/NH₂-PDMS film, but the well-compatibility between epoxy matrix and MA-POSS has provided P(GMA/MA-POSS) film with much higher transmittance (98%) than PGMA/NH₂-POSS film (24%), PGMA/NH₂-PDMS film (27%) and traditional epoxy resin film (5%). The introduction of polysiloxane into epoxy matrix is confirmed to create hybrids with strong adhesive strength (526-1113N) and high thermos-stability (T_g=262-282°C), especially the cage-structured P(GMA/MA-POSS) hybrid (1113N and 282°C), but the flexible PDMS improves PGMA/NH₂-PDMS hybrid with much higher storage modulus (519MPa) than PGMA/NH₂-POSS (271MPa), which suggests that PDMS is advantage in improving the film stiffness than POSS cages. However, cage-structured P(GMA/MA-POSS) and PGMA/NH₂-POSS indicate higher permeability than PGMA/NH₂-PDMS and traditional epoxy resin. Comparatively, the cage-structured P(GMA/MA-POSS) hybrid is the best coating in transparency, permeability, adhesive strength and thermostability, but linear-structured PGMA/NH₂-PDMS hybrid behaviors the best coating in mechanical property.