Preparation of phosphinated bisphenol from acid-fragmentation of 1,1,1-tris(4-hydroxyphenyl)ethane and its application in high-performance cyanate esters

Cyanate esters have received considerable attention because of their exceptional properties, such as good thermal stability, low water absorption, and low dielectric properties. They have been found to be particularly useful in the preparation of electrical and structural laminates, potting formulations, molding formulations, etc. Dicyanate esters are generally prepared by the reaction of bisphenol and cyanogen bromide in the presence of triethylamine at low temperature. The cyanate group undergoes trimerization to form the s-triazine ring and generates a thermoset with high cross-linking density. A large variety of cyanate esters with different backbone structures and properties have been synthesized and are summarized by Shimp et al. and Lin et al., respectively. Over the past decade, many new cyanate esters were developed. For example, Wang et al. prepared phenolphthalein-based cyanate esters with high-Tg for higher temperature applications. Snow et al. prepared fluoromethylene cyanate ester with lower Tg, dielectric constant, critical surface tension and water absorption. Lin et al. prepared a dipentene-containing cyanate ester with low moisture absorptions and low dielectric properties due to the hydrophobic character of the aliphatic dipentene structure. Although poly(cyanate esters) display promising properties, the lack of flame retardancy is a drawback of cyanate ester for electronic applications, where meeting a flame retardancy standard, UL-94 V-0, is required. Literatures have reported that the flame retardancy of cyanate esters can be greatly enhanced by the incorporation of phosphorus element.