Epoxy hybrid networks with high mass fraction molecular-level dispersion of pendant polyhedral oligomeric silsesquioxane (POSS)

Abstract

A novel high shear continuous reactor method was developed to obtain molecular level incorporation of polyhedral oligomeric silsesquioxane (POSS) containing one amine group and seven isobutyl groups into epoxy network as pendant cage. The method consisted of optimizing reaction time and temperature for the synthesis of POSS-epoxy precursor in a high shear continuous reactor. A full conversion of POSS into POSS-epoxy precursor was achieved within 30–40 s of reaction time in a continuous reactor for all molar compositions from 1:140 to 1:1.05 in comparison to a batch process with the reaction time of 18 h. The structure of this precursor at the end of the reaction, determined by silicon Nuclear Magnetic Resonance spectroscopy (29Si NMR), was close to the ideal one. The distribution of reaction product was determined by size exclusion chromatography (SEC). The reaction product containing up to 1:3-mol ratio of POSS: epoxy molecules showed ‘epoxy-POSS-epoxy’ precursor as a primary product in comparison to 1:2 and 1:1.05-mol ratios with higher molecular weight precursor as the primary product. Hybrid networks containing up to 50 wt % POSS were prepared by curing these precursors with an aromatic amine curative 4, 4'diamino diphenyl methane (DDM). The resulting networks are completely transparent and no phase separation was observed by SEM and TEM in the course of polymerization despite the incompatibility of the isobutyl groups attached to the POSS with the aromatic epoxy-amine networks. In addition to that, DMA and TGA results prove that the introduction of high shear continuous reactor promotes the dispersion of pendant POSS to a molecular level into epoxy networks.