Cyanate ester resins curing reaction

Figure 3.47. A comparison of cure reaction monitoring by a univariate method (CN band intensities) and a multivariate method (PCI scores) for a cyanate ester resin. Adapted from Cooper (1999).

Figure 2.37 Reaction schemes for the synthesis and curing of liquid fluorinated cyanate ester resin. Reproduced with permission from M. Laskoski, D.D. Dominguez and T.M. Keller, Journal of Materials Chemistry, 2005,15,161. 2005, The Royal Society of Chemistry...

A modified epoxy matrix for Kevlar FRP composites was produced from ep>oxy/polyphenylene oxide (PPO) blends cured with multifunctional cyanate ester resin [94]. The effects of the PPO content on the cme behavior in the cyanate ester-cmed epoxy were investigated with FTIR. The cme reaction in the ep>oxy/PPO blends was faster than that of the neat epoxy system. FTIR analysis revealed that the cyanate fimctional group reactions were accelerated by adding PPO and that several co-reactions had occurred. Thermal mechanical analysis showed that the thermal stability of the epoxy/PPO matrix is improved by adding PPO. In the respective compursites, the ISS values between Kevlar fiber and the epoxy/PPO blends are almost the same as those between Kevlar fiber and neat epoxy. The ILSS in the respective laminates increases with the PPO content, which was attributed to an increase in the composites ductility. 

Lin, C. H., Synthesis of novel phosphorus-containing cyanate esters and their curing reaction with epoxy resin, Polymer, 2004, 45, 7911-7926. 

Despite their many attractive features, the search for further improvements in performance and reduction in cost of cyanate esters is never ending and a large number of studies have been devoted to matrix modification through blends, and co-curing of these systems. Reactions of cyanate esters with a variety of functional groups like amines [169], hydroxyl [34, 66], epoxy [170-172], phenols, etc., have been reported, among which the most studied are reactions with epoxy [173,174]. Epoxy-cyanate blends are common and found in many commercial and patented resin formulations. 

The basic chemical reactions, used to synthesize monomer and polymer resins and the chemistry involved in the use of curing agents to polymerize the resins, have been extensively studied and are well documented. This section serves as a summary only of those polymers that are primarily used in adhesives formulations for electronic applications. Among these polymers are the epoxies, silicones, polyurethanes, polyimides, acrylates, cyanate esters, and cyclo-olefins. Further technical detail for these polymers maybe acquired through literature searches in the transactions of the American Chemical Society (Polymer Group), Society of Plastics Engineers (SPE), and the Society for the Advancement of Materials and Process Engineers (SAMPE). 

It has been shown that in many cases for thermoset systems, there is a quantitative relationship between the chemical conversion of the thermoset and its Tg value, independent of the time-temperature cure history (111). This is very convenient from an applications standpoint because measurement of Tg is equivalent to a direct measurement of conversion. It implies that either the molecular structure at a given degree of conversion is the same, regardless of the reaction path, or that differences in the structures produced for different reaction paths do not affect Tg. While a Tg-degree of cure relationship has been found valid for many epoxy-amine and other thermoset materials, it has been observed not to hold in some cases, which include some epoxy-DICY, cyanate-ester, and phenolic systems. It has also been found not to hold for a given resin system cured by two different methods such as thermal and microwave (112) or thermal and electron beam cures (113). 

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. 

Su WFA (1993) Thermoplastic and thermoset main-chain liquid-crystal polymers prepared from biphenyl mesogen. J Polym Sci Polym Chem 31 3251-3256 Su WFA, Chuang CM (2002) Effects of chemical structure changes on curing reactions and thermal properties of cyanate ester-cured rigid-rod epoxy resins. J Appl Polym Sci 85 2419-2422... 

H.F. Bluhm, USP 3256214(1966) CA 65, 9132(1966) [Prepn of explosive polyurethane resins, which are suitable for use as sensitive coatings for AN blasting compns and for prepn of foamed resin expls is described. The resins, which can be cured at RT, are prepd by reaction of an org poiyiso-cyanate with a nitric acid partial ester of a polyhydroxy compd including a component contg > OH groups reactive with the isocyanate. For example, equal parts by wt of an-hydroenneaheptitol nitrate (13.77 wt %N as... 

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