Superiority of nanosized over microsized hyperbranched polymer second phase in modifying brittle epoxy resin



A hydroxyl-functionalized hyperbranched polymer (HBP, H30) is used to modify 4,4′-diaminodiphenylsulfone-cured bisphenol-A type epoxy resin and a separate phase structure of modified epoxy resins is observed. The effects of the H30 second phase size on the mechanical properties of modified epoxy systems are investigated systematically. The dependence of the toughening mechanisms on the HBP particle size is reported for the first time. It is shown that the nanosized H30 second phase is superior over microsized counterparts in modifying brittle epoxy resin. The tensile strength is slightly enhanced by the introduction of nanosized H30 second phase, whereas the strength is significantly reduced by the addition of microsized H30 phase. The failure strain and impact strength are obviously enhanced by the introduction of nanosized H30 second phase at low contents, whereas these properties are reduced by the addition of microsized H30 second phase at high contents. Finally, differential scanning calorimetric and thermogravimetric analyses are conducted to examine the effects of the HBP content on the glass transition temperature and the thermal stability, respectively. The glass transition temperature is slightly reduced while the thermal stability is not obviously influenced by the introduction of H30 second phase. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011