Recent Progress of High Performance Thermosets Based on Norbornene Functional Benzoxazine Resins

With the growing demand for high performance polymeric materials in industry, several types of thermosets such as bismaleimides, advanced epoxy resins, cyanate esters, and phenolic resins have been widely investigated to improve the performance of thermosetting products. Among them, benzoxazine resins have received wide attention due to their extraordinarily rich molecular design flexibility, which can customize our needs and adapt increasing requirements. To further improve the properties of polybenzoxiazines, researchers have found that the introduction of a norbornene functional group into the benzoxazine moiety can effectively improve the comprehensive performance of polybenzoxazine thermosets. This article focused on reviewing the recent development of high-performance thermosets based on norbornene functional benzoxazine thermosetting resins.

APPLICATION OF CYANATE ESTER MATERIALS (review) Part 1. Aviation and space structures

The review concerns the major application of materials based on cyanate ester resins in various branches of technology, indicating examples of implementation in modern devices. This article being the first part of the review highlights the cyanate esters implementation in the development of materials for aviation and space technology. The paper presents the most significant properties of polycyanurates in relation to their application. Information about the development of new cyanate ester resin-based composite materials for aircrafts and space shuttles is provided.

Effects of trace phenolic hydroxyl groups on the cure behaviours and properties of cyanate esters

To improve the curing properties of cyanate esters and retain their heat resistance, dielectric properties and adhesion properties, modified cyanate copolymers were prepared by blending bisphenol A cyanate (BADCy) ester with phenol, hydroquinone (HO), resorcinol and phloroglucinol (LO). Differential scanning calorimetry analysis (DSC) and Fourier transform infrared spectroscopy were used to investigate the cure behaviours of the prepared compounds. The prepared materials were compared with the BADCy ester containing trace of cobalt acetylacetonate (CoAt). The CoAt/BADCy blend modified by HO exhibited better curing properties. The exothermic peak temperature ( T p) of the CoAt/BADCy blend dropped to 169°C after introducing 1 wt% HO, likely due to the hydroxyl functional groups at the para position of the benzene ring resulting in higher symmetry and reactivity for the HO. In addition, compared with original CoAt/BADCy, the cyanate esters modified by phenolic hydroxyl groups demonstrated higher adhesive properties and a similar glass transition temperature (approximately 290°C) as well as stable dielectric properties. The experimental results indicate potential applications of the cyanate ester under high-temperature conditions.

Fast pyrolysis bio-oil from lignocellulosic biomass for the development of bio-based cyanate esters and cross-linked networks

Fast pyrolysis of pine wood was carried out to yield a liquid bio-oil mixture that was separated into organic and aqueous phases. The organic phase (ORG-bio-oil) was characterized by gas chromatography–mass spectroscopy, 31P-nuclear magnetic resonance spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. It was further used as a raw material for producing a mixture of biphenolic compounds (ORG-biphenol). ORG-bio-oil, ORG-biphenol, and bisphenol-A were reacted with cyanogen bromide to yield cyanate ester monomers. Cyanate esters were characterized using FTIR spectroscopy and were thermally cross-linked to develop thermoset materials. Thermomechanical properties of cross-linked cyanate esters were assessed using dynamic mechanical analysis and compared with those of cross-linked bisphenol-A-based cyanate ester. ORG-biphenol cyanate ester was observed to have a superior glass transition temperature (350–380°C) as compared to bisphenol-A cyanate ester (190–220°C). Cyanate esters derived from bio-oil have the potential to be a sustainable alternative to the bisphenol-A-derived analog.

Synthesis of Cyanate Esters Based on Mono-O-Methylated Bisphenols with Sulfur-Containing Bridges

We described a synthetic approach to bisphenol-based monocyanate esters based on mono-O-methylation of parental bisphenols followed by cyanation of the residual phenolic hydroxyl. Structures of the synthesized compounds were determined by the application of IR, NMR 1H and 13C spectroscopies, EI and MALDI mass spectrometry, and purity of the final product was controlled by HPLC. We showed that stability of the cyanate esters depends on the nature of the bridging group. Temperature range of thermally initiated cyclotrimerization of synthesized monocyanate ester, as well as reaction enthalpy, was determined by differential scanning calorimetry (DSC).