Catalysis for highly thermostable phenol-terephthalaldehyde polymer networks

Abstract

There is a crucial need to eliminate formaldehyde (F) from high-performance thermoset formulations. We propose herein the study of innovative phenol (P)-terephthalaldehyde (TPA) resole, synthesized under basic conditions. For aerospace applications, alkali-or alkaline-earth-based catalysts should be avoided because they degrade the polymer performances in real conditions. To address this issue, we successfully employed DBU to catalyze the resole formation and compared the mechanisms and performances to the usual NaOH-catalyzed formulation. Insights into the undergoing chemical reactions of crosslinking were given by IR and NMR spectroscopies together with thermal analyses (DSC and TGA). We proposed a two-step mechanism pathway, directly arising from the multiple reactions occurring with TPA (compare to only two with F). An in-depth thermo-kinetics study was efficient to compare both NaOH and DBU catalyzed reactions (performed using multiple heating rates DSC data and isoconversional computational method of Vyazovkin). Finally, TGA results showed that these new resoles presented increased thermal performances compare to commercial PF. TOC This paper presents innovative and highly-performant phenol-terephthalaldehyde thermosets and gives insights into the catalysis and mechanisms of polymerization.

Aromatic dialdehyde-based bisbenzoxazines: The influence of relative position of oxazine rings

“…The theoretical considerations and computational detail can be found in our previous articles. [17,20,21]…”

“…[31] These results are in line with our work on formaldehyde-free resoles, whose crosslinking mechanisms involved several chemical reactions. [17,20,21]…”

Versatile Method To Reduce the Free Formaldehyde Content in Phenolic Resins for High-Temperature Applications

“…For example, sodium sulfite or sodium metabisulfite contain alkalis that should be avoided in thermal protection systems. 39 For the same reason, although NaOH is often chosen as a catalyst for the synthesis of resoles, ammonia catalysis was preferred in this work. Furthermore, resins synthesized with ammonia versus NaOH are described as being more heat resistant, having a higher molecular weight, having lower water solubility, higher glass transition temperature, and being slightly less crosslinked (associated with better mechanical properties).…”

“…In addition, although some additives can maintain or improve thermostability, they are not compatible with aerospace applications. For example, sodium sulfite or sodium metabisulfite contain alkalis that should be avoided in thermal protection systems …”

Terephthalaldehyde–Phenolic Resins as a Solid-Phase Extraction System for the Recovery of Rare-Earth Elements

“…The replacement of the formaldehyde was recently proposed using several bio-based, non-hazardous aldehydes with phenol [24][25][26]. Among the aldehydes studied, terephthalaldehyde (TPA) with the presence of a second aldehyde in para-position showed the best reactivity [25][26][27]. Additionally, the synthesized phenol-terephthalaldehyde resin displayed a highly crosslinked network which is an interesting property for the purpose of using them in solid-liquid extraction processes.…”