Esters aromatic cyanate

The hydrolytic susceptibility of the fluoromethylene cyanate ester is greater than that of the aromatic cyanate ester. Direct contact with water results in measurable hydrolysis to the carbamate in a 24-h period for the former while the latter is unaffected.9... 

It has been established by a variety of techniques that aromatic cyanate esters cyclotrimerize to form cross-linked cyanurate networks.1 Analogously, the fluoromethylene cyanate monomers cure to cyanurate networks. In addition to the 19F-NMR spectra shown in Figure 2.3, evidence includes an up-field shift of the methylene triplet (1H-NMR, 0.21 ppm 13C-NMR, 9.4 ppm), the disappearance of the cyanate functional group (IR, 2165 cm4 13C-NMR, 111.9ppm) and the appearance of the cyanurate functional group (IR, 1580 and 1370 cm4 13C-NMR, 173.6 ppm).9 Typically, monomers are advanced to prepolymers by thermal treatment at 120°C or just above the melting point. The prepolymers are then cured at 175°C and are postcured at 225°C. 

The curing reaction can be carried out thermally or with the addition of a catalyst. The thermal cure is strongly influenced by impurities associated with the synthesis. The greater the degree of monomer purity, the more slowly the thermal cure proceeds. If the monomer is sufficiently purified, the cure rate can be predictably controlled by the addition of catalysts. As with the aromatic cyanate esters, the fluoromethylene cyanate esters can be cured by the addition of active hydrogen compounds and transition metal complexes. Addition of 1.5 wt% of the fluorinated diol precursor serves as a suitable catalyst.9 The acetylacetonate transition metal salts, which work well for the aromatic cyanate esters,1 are also good catalysts. 

The fluorine content, density, critical surface energy, glass transitions, thermal expansion coefficient above and below the glass transition, and 300°C isothermal thermogravimetric stabilities of the fluoromethylene cyanate ester resin system with n = 3, 4, 6, 8, 10 are summarized Table 2.2. Also included for the purpose of comparison are the corresponding data for the aromatic cyanate ester resin based on the dicyanate of 6F bisphenol A (AroCy F, Ciba Geigy). 

An example of cyclotrimerization reactions is the homopolymerization of aromatic cyanate esters, forming triazine rings (Fig. 3.17). As these particular stepwise polymerizations cannot be described by the equations developed so far, we will consider them in this section with the usual assumptions for an ideal polymerization. 

Another type of film investigated recently has been aromatic cyanate esters prepared from the Ciba-Geigy products AroCy L-10 (l,l-bis(4-cyanatophenyl) ethane) and AroCy B-30 (the prepolymer form of 2,2/-bis(4-cyanatophenyl) isopropylidene, AroCy B-10) [89], The chemical structures of these molecules are shown in 4. Spectral measurements from these aromatic cyanate ester ma-... 

Heterocyclic compounds bearing a mercapto group ortho to a ring nitrogen react with aromatic cyanate esters (2 mol) to yield fused structures... 

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