Effect of Segmental Configuration on Properties of n-Propyl-Bridged Polycyanurate Networks

Abstract

The effect of the chemical configuration of network segments on the physical properties, cure properties, mechanical performance, and chemical stability of polycyanurate networks was investigated via synthesis, network formation, and characterization of an isomeric series of npropyl-bridged cyanate ester monomers. Configurations that provide cyanurate oxygen atoms with either nearby methyl groups or nearby bridge groups exhibited decreased moisture uptake by up to 50%, along with a roughly 20−40 °C reduction in the loss in glass transition temperatures due to hydrolysis, for networks immersed in 85 °C water for 96 h. In ortho,para-linked aryl cyanates, dry glass transition temperatures of cured networks were reduced compared to analogous para,para-linked networks by only about 10 °C, compared to a reduction of 30 °C in ortho-methylated cyanate ester networks, leading to higher "wet" glass transition temperatures in the ortho,para-linked networks. Neither methyl groups nor bridge groups in a position ortho to the reactive cyanate ester groups prevented the creation of networks with >99% conversion at cure temperatures of 230 °C. Networks with placement of methyl groups in a position ortho to the cyanate ester exhibited char yields in nitrogen at 600 °C of 46−47% compared to 43% for networks with methyl groups in the corresponding meta position, regardless of whether a sterically hindered environment was present around the cyanurate oxygen. These results illustrate the manner in which the chemical configuration around reactive groups can substantially modify the properties of networks even when the number density and type of reactive group present do not change.

Insights into Melting Behavior of Propyl-Bridged Di(cyanate ester) Monomers through Crystal Packing, Thermal Characterization, and Computational Analysis

“…A consistent melting endotherm for monomer 1 was not attainable. Experience in handling this monomer revealed that the supercooled liquid is stable for very long periods, with crystal growth requiring time periods that are impractically long for DSC analysis. Among the remaining isomers 2 – 4 , there is considerable variation in both the enthalpy (range equal to about 50% of the average value) and entropy (range equal to about 40% of average) of melting when measured at the melting point.…”

“…The four dicyanate ester monomers were prepared and purified according to literature methods. , Solvents were obtained commercially and used as received.…”

“…14 An important unresolved question from that work is whether the same approach can be applied more generally, including to systems with other types of organic moieties present. In particular, the propylbridged aryl di(cyanate ester)s, shown in Scheme 1, are a class of recently synthesized compounds that exhibit an unexpectedly wide range of melting points, 15,16 although the reasons for this surprising behavior were not previously explored in detail.…”

Triptycene-Based Microporous Cyanate Resins for Adsorption/Separations of Benzene/Cyclohexane and Carbon Dioxide Gas

“…Microporous cyanate resins represent a new class of MOPs developed in our group − since 2009 that potentially extend the applications of thermosetting cyanate resins − to other high-tech fields, e.g., adsorption of gases and organic vapors. Using multifunctional cyanate monomers, upon heating, every three OCN groups are thermally cyclotrimerized to form a triazine ring, which acts as net node in the hyper-cross-linked microporous cyanate resin networks.…”

Design and Evaluation of a Cyanate Ester Containing Oxaspirocyclic Structure for Electronic Packaging

“…This development mainly focuses on improving the thermal properties, dielectric properties, and flame retardancy of the resin. Zhan et al synthesized an isomeric series of n-propyl-bridged cyanate ester monomers [15]. They reported that when cyanurate oxygen atoms were nearby methyl groups or bridge groups, the resin exhibited a decreased moisture uptake by up to 50%, along with an approximately 20-40 °C decrease in the glass transition temperature.…”