Formulation and physical properties of cyanate ester nanocomposites based on graphene

ABSTRACT We report the thermal, mechanical, and diffusion properties of bisphenol E based polycyanurate nanocomposites with three forms of graphene derived from sequential processing of the same carbon nanostructure. Edge‐functionalized graphene nanoplatelets (GNP) were converted to graphene oxide (GO), then heated to produce thermally reduced graphene oxide (TRGO). All three reinforcements were individually mixed with the dicyanate ester of bisphenol E (LECy) at low loading levels and cured to form polycyanurate nanocomposites. GNP, with very low oxygen functionality, was incompatible with the cyanate ester, while the highly oxidized GO formed well‐dispersed (though not exfoliated) nanocomposites, with the TRGO forming a good dispersion on mixing but phase separating during cure. The addition of GO, and, to a lesser extent, TRGO, resulted in improved mechanical properties, particularly fracture toughness, with the addition of TRGO having a modestly negative effect on the glass transition temperature. Surprisingly, neither GO nor TRGO addition was effective at slowing down the diffusion of water in the polycyanurate, with the addition of both resulting in increased equilibrium moisture uptake. It thus appears that the trade‐off between dispersion and the required level of oxygen functionality acts in a manner to frustrate attempts at minimizing the permeation of water by addition of graphene‐based reinforcements. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1061–1070 Three forms of graphene, namely graphene nanoplatelets (GNPs), graphene oxide (GO), and thermally reduced graphene oxide (TRGO), are used as reinforcing agents in dicyanate ester of bisphenol E (LECy). Although both GO and TRGO are well dispersed in monomeric LECy, TRGO phase separates during cure. Both composite materials display higher fracture toughness but a higher equilibrium water uptake than neat LECy. The results presented here provide important new information for understanding the performance of graphene/polymer nanocomposites.