Effects of crosslink density on mechanical properties of high glass transition temperature polycyanurate networks

Abstract

Polycyanurate networks of different architecture were synthesized using different curing cycles. Networks with a variable extent of reaction were obtained; the small variation of the cyanate conversion (0.8 to 1) corresponds to a large variation of glass transition temperature (150-290ЊC) and crosslink density. The mechanical behavior at small and large deformations and the fracture toughness were examined at room temperature and related to the network structural parameters. To explain the puzzling variation of the yield stress and yield strain with the cyanate conversion, recovery experiments were conducted to discriminate anelastic deformation from plastic deformation.

Synthesis and properties of a liquid oligomeric cyanate ester resin

“…Curing 5 in the presence of 8 phr of the copper (II) naphthenate/nonylphenol catalyst system under identical conditions did not change the T g value. These observations indicated that thermoset 6 formed from CE 5 may be completely cured by post-curing to a maximum temperature of 250 8C for 5 h. The lower T g value for 6 (140 8C) relative to 7 (255 8C) cured under identical curing conditions was predictable since the crosslinking density was reduced [39]. The T g values determined by DSC and rheometric analyses were in agreement.…”

PALS free volume and mechanical properties in dimethacrylate‐based thermosets

“…It appears that although the free volume may facilitate small‐scale molecular motion, the higher crosslink densities of the DVB comonomer systems restrict the large‐scale segmental motion required for plastic deformation and thus toughness. A plot of the free‐volume fraction and Charpy impact strength as a function of the amount of DVB added in the formulation (Fig 6), shows a trend opposite to that observed in epoxy networks19 and also in cyanate networks 64. In these cases, extra free volume was believed to facilitate plastic deformation and therefore lower network brittleness.…”

Influence of backbone structure, conversion and phenolic co-curing of cyanate esters on side relaxations, fracture toughness, flammability properties and water uptake and toughening with low molecular weight polyethersulphones

“…Whereas in [3][4][5][6][7] the effect of conversion is investigated only for one cyanate ester monomer, two different cyanate ester monomers are compared here to show the effect of backbone structure. In the first part of this work high precision thermomechanical data (measured using a custom-built torsional pendulum) and precise measurements of conversion form the basis of an analysis over an extended range of conversion.…”

“…Whereas the effects of conversion on free volume have been discussed in the literature [3,7], the relationship between free volume and side relaxations has not been considered so far. Georjon and Galy [7] discuss the influence of conversion on volume-related properties, and the influence of conversion on side relaxations is discussed for B10 (DCBA) in [5,6]. The authors discuss the relationship between the room temperature modulus and the intensity of low temperature side relaxations (denoted as -relaxation).…”