Effect of Nanoparticle Functionalization on the Performance of Polycyanurate/Silica Nanocomposites

Abstract

The impact of silica functionalization in determining the performance of polycyanurate networks polymerized from 1,1-bis(4-cyanatophenyl)ethane, known commercially as Primaset LECy, reinforced with modified fumed silica, was elucidated through systematic comparison of the properties of nanocomposite networks in which the silica surface treatment was altered. Three types of surfaces were investigated: moderately acidic (unmodified silanol), neutral (alkylsilane modified), and slightly basic (3-aminopropylsilane modified). In terms of cyanate ester cure, the acidic surface proved to be moderately catalytic, the neutral surface mildly catalytic due to slight residual silanol content, and the basic amino-functional surface mildly inhibitory. In terms of network performance, the amino-functional surface led to significant degradation of the network at elevated temperatures, while the silanolfunctional surface outperformed the alkyl-functional surface in terms of protection against hydrolytic degradation. In agreement with expectations, the addition of 2−5 wt% of relatively well-dispersed silica nanoparticles had negligible impact on the fracture toughness of the cyanurate networks. Overall, these results demonstrate that the functionalization of nanoparticle additives for polycyanurate networks is an important determinant of performance and must be taken into consideration in the development of polycyanurate nanocomposites, even at levels that are too low to strongly affect mechanical properties. ■ INTRODUCTIONNetworks derived from cyanate ester monomers, known as polycyanurate networks, 1−4 are utilized in several of the most demanding high-performance applications currently known. These include thermonuclear fusion reactors such as ITER, 5−7 where, in blends with epoxy resins, they impart critical resistance to neutron irradiation. Also included are interplanetary space probes such as the MESSENGER mission to Mercury 8 and the Mars Curiosity rover, 9 where mechanical strength and toughness across a broad temperature range and low off-gassing are important considerations. In addition, cyanate esters have been utilized in space structures closer to Earth, such as the James Webb Space Telescope 10 and the Orion Earth re-entry heat shield, 11 where dimensional stability and flame resistance, respectively, drive materials requirements. Numerous other applications such as filament wound aerospace structures 12 and high-temperature microelectronic circuit boards 13 also make use of the outstanding thermal, mechanical, and electrical properties of polycyanurate networks.In most practical applications, polycyanurate networks (polycyanurates), even when serving as composite resins, are not utilized as single-component materials systems. Rather, they are formulated with a variety of additives and reinforcements in order to maximize performance in their intended applications.One of the most common, and most important, of these reinforcements is silica. The properties of polycyanurate/silica composites have been investigated and...

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