Dicyanates, synthesis

Only after pure, aromatic dicyanates had become available (45) a patent by Schminke et al. (40) described the synthesis of poly-(iminocarbonates) with molecular weights of about 50,000 by the solution polymerization of a diphenol and a dicyanate (Scheme 2). Bulk polymerization was also claimed to be possible. 

This feature of the interfacial preparation of poIy(iminocarbon-ates) has an important consequence for the synthesis of copolymers if the dicyanate component is structurally different from the diphenol, partial hydrolysis of the dicyanate will lead to the presence of two structurally different diphenol components that will compete for the reaction with the remaining dicyanate. The interfacial copolymerization will therefore result in a random copolymer. On the other hand, during solution polymerization no hydrolysis can occur. Since the dicyanates can only react with diphenols and vice versa, solution polymerization results in the formation of a strictly alternating copolymer. 

Synthesis of Dicyanates. All dicyanates were prepared according to previously published procedures (2). For IR spectral data see Kohn and Langer (2), for elemental analyses, see reference 10. A specific procedure for the preparation of Z-Tyr-Tyr-Hex-dicyanate has been published (75). 

Organic molecules have been used as catalysts from the early age of synthetic chemistry. Indeed, the discovery of the first organocatalytic reaction is attributed to J. von Liebig, who found - accidentally - that dicyan is transformed into oxa-mide in the presence of an aqueous solution of acetaldehyde (Scheme 1.1). Subsequently, this efficient reaction found industrial application by forming the basis of the Degussa oxamide synthesis. 

In addition to the high-pressure polycondensation reactions mentioned above, we have studied the high-pressure polyaddition for the synthesis of high-temperature aromatic polymers such as polyaminoimide from bismaleimide and aromatic diamine, polycyanurates from aromatic dicyanates, and polyiso-cyanurates from aromatic diisocyanates [34,36-40]. 

A comprehensive review on the synthesis and the polycyclotrimerization of cyanates was published in the USSR in 1977 (with 160 references) [3], More than 50 dicyanates... 

Review on the synthesis and reactions of cyano acetylene and dicyan oecetylene E. Ciganek,... 

A variety of CEs with tailorable physico-chemical and thermo-mechanical properties have been synthesized by appropriate selection of the precursor phenol [39,40]. The physical characteristics like melting point and processing window, dielectric characteristics, environmental stability, and thermo-mechanical characteristics largely depend on the backbone structure. Several cyanate ester systems bearing elements such as P, S, F, Br, etc. have been reported [39-41,45-47]. Mainly three approaches can be seen. While dicyanate esters are based on simple diphenols, cyanate telechelics are derived from phenol telechelic polymers whose basic properties are dictated by the backbone structure. The terminal cyanate groups serve as crosslinking sites. The polycyanate esters are obtained by cyanation of polyhydric polymers which, in turn, are synthesized by suitable synthesis protocols. Thus, in addition to the bisphenol-based CEs, other types like cyanate esters of novolacs [37,48], polystyrene [49], resorcinol [36], tert-butyl, and cyano substituted phenols [50], poly cyanate esters with hydrophobic cycloaliphatic backbone [51], and allyl-functionalized cyanate esters [52] have been reported. 

Fainleib A, Grigoryeva 0, Hourston D. Synthesis of inhomogeneous modified polycyanurates by reactive blending of bisphenol A dicyanate ester and polyoxypropylene glycol. Macromol. Symp., 164, 429-442 (2001). 

Polyurethane/polycyanurate grafted semi-IPNs were prepared by polycyclotrimerization of dicyanate ester of bisphenol A (DCEBA) in the immediate presence of TPU, as described in Section 3.1. During semi-IPN synthesis, at... 

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