Formation of new thermosets by the reaction of cyanates with thiophenols

Abstract

Sulfur-containing aromatic thermosets, mainly consisting of aryloxy- and arylthio-substituted 1,3,5-triazines, have been prepared through the reaction of difunctional cyanates with mono- and difunctional aromatic thiols. A straightforward three-step reaction scheme is proposed and verified by the identification of key substances: (1) the addition of thiol and cyanate groups, (2) the stepwise addition of (thio)imino carbonic esters with one another, and (3) the ring closure of chain-extended (thio)imino carbonic esters to form 1,3,5-triazines. Reactions of types 2 and 3 are associated with an abstraction of phenol or thiophenol, which can enter into reaction 1 again. Characterization Of the curing behavior of dicyanate of bisphenol A with thiophenol as well as dimercaptodiphenyl sulfide by differential scanning calorimetry shows that the reaction rates are significantly enhanced by the admixture of thiols to the cyanate. Dynamic mechanical analysis of resulting thermosets showed that large amounts of comonomers can be incorporated into the network resulting in a decrease of glass temperature but increase of fracture toughness. Finally, the fully cured thermosets resulting front the reaction of dicyanate of bisphenol A with different admixtures of dimercaptodiphenyl sulfide were characterized by cone calorimetry to get information about flame retardancy. The flame retardancy is influenced by incorporation of dimercaptodiphenyl sulfide into the triazine network only slightly.

Ambient temperature cross-linking of a sustainable, cardanol-based cyanate esterviasynergistic thiol–ene copolymerization

“…A small peak (∼2150 cm −1 ) was also formed and is attributed to a trace of residual imidothioate formed by nucleophilic attack of a thiol group on the carbon of a cyanate ester group. 73 This reaction enhances the nucleophilicity of the nitrogen and promotes the formation of the cyanurate ring system (Scheme 1). 74 To our knowledge, this is the first example of ambient temperature cure of a cyanate ester resin.…”

Examining the thermal degradation behaviour of a series of cyanate ester homopolymers

“…These applications are the consequence of their high mechanical strength, high moisture resistance, low dielectric loss, low volatility during the cure and low toxicity . In recent years, many new cyanate monomers have emerged, especially the dicyanates containing aromatic ether, ketone, 2,7‐dihydroxynaphthalene, polyurethane, thiophenols, silicones and phosphorus . Although cyanate esters are known to exhibit excellent thermal properties, investigations into the thermal behaviour, thermal stability and thermal degradation kinetics using different mathematical models under non‐isothermal and isothermal conditions are more limited beyond very basic cyanate esters .…”

Synthesis, cure kinetics, and thermal properties of the Bis(3‐allyl‐2‐cyanatophenyl)sulphoxide/BMI blends

“…Cure kinetics of the neat cyanate ester resins is extensively available in literature 17–24. Bur for blends, reports on the cure kinetics is scarce.…”