Properties of unreinforced cyanate ester matrix resins

Abstract

The cyclotrimerization reaction by which dicyanate ester monomers are polymerized to form polycyanurates is a most intriguing one which has prompted much research to elucidate the mechanism (the topic is discussed further in chapters 2 and 3). The cure produces a polymer with many interesting properties which commend its use in high performance, technological applications (chapter 10). The resulting thermoset network has high toughness (as measured by impact strength G _IC, strain-at-break and peel strength) allied to high glass transition temperature, T _g. This combination of properties is unusual in 250°C T _g resins and is attributed [1] to the presence of ether-oxygen linkages, low crosslink density and apparent high free volume in the cured state. Equally unusual in high-T _g resins are exceptionally low dielectric constant (D _k = 2.66–3.08) and dissipation factor (D _f = 1 × 10⁻³to 6 × 10⁻³) measured in the neat resin at 1 MHz and 25°C. These phenomena are described in greater detail in chapter 8, but it is postulated [1] that high free volume and relatively weak dipoles in the polycyanurate may contribute to these low loss properties. This chapter addresses some of the properties (particularly thermomechanical) associated with neat resin specimens of cyanate esters in relation to competitor high temperature resin systems.