Cyanates, cyclotrimerization

The epoxide/cyanate compositions contain catalysts of cyanate cyclotrimerization and oxazoline ring formation. Curing agents for epoxide resin are mentioned in... 

It can be assumed that two separate networks with no covalent bonds between the UPR and the cyanate-based triazine network are formed. The possible addition of terminal hydroxyls from the unsaturated polyester to the —C = N bonds in BPA/DC is rather improbable as the addition of alcohols to cyanates, leading to iminocarbonate derivatives (Scheme 8), only occurs in the presence of strong alkali catalysts [134], The cyanate cyclotrimerization has been evidenced from disappearance of the 2230 and 2270 cm-1 and the appearance of 1370 and 1560 cm-1 absorption bands in the infrared spectra of the crosslinked IPN. 

Influence of carbon fiber fillers on the formation and phase structure. The effect of two carbon fiber fillers a basic filler (CF) and CF with a surface modification by orthophosphoric acid residues (PCF) on the kinetics of epoxypolycyanurate (EPCN)/TPU grafted semi-IPN formation and phase structure was studied [50,51]. The network component in TPU/EPCN semi-IPNs was synthesized from the reactive blend of EO and DCEBA (Section 3.2.1). Acceleration of the occurring reactions was observed by the introduction the both carbon fiber fillers into the semi-IPNs studied, as seen in Figure 10 from the kinetic curves for a semi-IPN with 20 wt% of TPU. This acceleration is assumed to be associated with the additional chemical reactions between the components, with the catalytic effect of TPU on cyanate cyclotrimerization [41,42], and with interactions of polymers with the filler surface discussed in [50]. 

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. 

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. 

Figure 3.17 Cyclotrimerization of cyanates leading to triazine rings.

Catalyst-free aromatic cyanates undergo cyclotrimerization only if they contain phenolic substances and water. Phenolic substances (non-reacted BPA and BPA monocyanate) are usually present in BPA/DC. Water evaporates gradually on... 

The linear addition copolymers of dicyanates are synthesized at equimolecular ratio of the comonomers. If one of the comonomers is used in excess, lower-molecular-weight polymers with corresponding end groups are obtained, which can further react with chain elongation agents. Terminal cyanate groups can be cyclotrimerized to obtain crosslinked polymers. 

The cyanate and the epoxide network can be bound by the reaction of phenolic hydroxyls contained in the partially cyclotrimerized cyanate prepolymer with the epoxy groups. In the first stage, a prepolymer was obtained by heating a mixture of BPA monocyanate and dicyanate with Co naphthenate as a catalyst (Scheme 15). 

Cyanates Epoxy-like processing at Self-cyclotrimerization 180-220 254-280 60-210... 

Some examples of what may be considered as actual thermosetithermoset blends are the epoxy and bismaleimide thermosets modified with aromatic dicyanate esters such as bisphenol A dicyanate. Aromatic cyanates crosslink by cyclotrimerization to form a network of triazine ethers. 

Bauer J, Hoper L, Bauer M. Cyclotrimerization Reactivities of Mono-and Difimctional Cyanates. Macromol Chem Physics. 1998. 

The cyclotrimerization of a cyanate ester (4,4 dicyanato-1,1 diphenylethane, CE) (Fig. 16), in the presence of a butadiene-acrylonitrile random copolymer terminated by non-functional groups (NFBN), has been analyzed [89]. 

Cyanate esters are a family of aryl dicyanate monomers that contain the reactive cyanate (-0-C=N) fimctional group. When heated, this cyanate functionality undergoes an exothermic cyclotrimerization reaction to form triazine ring connecting units, resulting in the formation of a thermoset polycyanate polymer. 

Cyanate/Cyanurate. When aryl cyanate esters are heated to 150 to 250°C, they cyclotrimerize to cyanuric acid esters (Fig. 3.62). They can be catalyzed by organo-metallic and active hydrogen compounds. When the monomer is a dicyanate such as bisphenol A dicyanate (Fig. 3.63), the result is a highly cross-linked heterocyclic polymer (Table 3.57). Using a novolac polycyanate has produced Tg and useful life over 300°C. 

FIGURE 3.62 Aryl cyanate ester cyclotrimerization to cyanuric acid ester. 

Figure 10.3 The formation of network via the cyclotrimerization of the cyanate group to the... 

The predominant curing pathway for cyanate ester is via cyclotrimerization using metal coordination catalysts. Three types of metal coordination catalysts are used metal naphthenates, metal acetylacetonates (AcAc), and metal octoates. Of these, Cu AcAc and Mn octoate are the most popular. Nonylphenol is also required as a cocatalyst. Reaction 5 shows the cyclotrimerization reaction of bisphenol A dicyanate to form the triazine network structure ... 

For very high Tg applications, dicyanates are cured without addition of epoxy modifiers leading to a very tight network via cyclotrimerization. The advantage of the cyanate ester family of monomers is the ability to formulate with epoxy resins. Typical resins in electronic applications are combinations of tailored epoxy monomers and oligomers along with cyanate esters. 

Boronic acids were cyanated under cyanide-free reaction conditions. Benzylthiocyanate served as cyanide equivalent and reacted with aryl, heteroaryl, and alkenyl boronic acids in the presence of a Pd catalyst and 1.5-3.0 equiv of CuTC (eq 23). CuTC has been shown to promote the cyclotrimerization of bicyclic w c-bromostannylalkenes (eq 24). ... 

The incorporation of s-triazine ring structures into thermoset resins has been practiced for a number of years by incorporation of melamine formaldehyde condensates into the formulations. Curing occurs through a further condensation reaction with the release of volatile material. Aryl cyanate esters cyclotrimerize to S triazine structures upon heating above 150°C without the release of volatiles. 

Cyanate ester resins (CERs) have found extensive use in applications where low-dielectric, high thermal stability materials are needed. Polymerization occurs by the cyclotrimerization of aryl cyanate ester groups... 

Preparation. In this communication, we focus on preparing ultra-thin polymer overlayers on disks starting with the cyanate ester monomer, 2,2 -bis(4-cyanatophenyl)isopropylidene (BCPP), supplied by Ciba Specialty Chemicals. Figure 4 shows the chemical structure of the BCPP monomer and the ring forming cyclotrimerization reaction that occurs when these monomers are heated in the presence of a suitable catalyst. 

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