Abstract
The synthesis of polymers from renewable resources is a burning issue that is actively investigated. Polyepoxide networks constitute a major class of thermosetting polymers and are extensively used as coatings, electronic materials, adhesives. Owing to their outstanding mechanical and electrical properties, chemical resistance, adhesion, and minimal shrinkage after curing, they are used in structural applications as well. Most of these thermosets are industrially manufactured from bisphenol A (BPA), a substance that was initially synthesized as a chemical estrogen. The awareness on BPA toxicity combined with the limited availability and volatile cost of fossil resources and the non-recyclability of thermosets implies necessary changes in the field of epoxy networks. Thus, substitution of BPA has witnessed an increasing number of studies both from the academic and industrial sides. This review proposes to give an overview of the reported aromatic multifunctional epoxide building blocks synthesized from biomass or from molecules that could be obtained from transformed biomass. After a reminder of the main glycidylation routes and mechanisms and the recent knowledge on BPA toxicity and legal issues, this review will provide a brief description of the main natural sources of aromatic molecules. The different epoxy prepolymers will then be organized from simple, mono-aromatic di-epoxy, to mono-aromatic poly-epoxy, to di-aromatic di-epoxy compounds, and finally to derivatives possessing numerous aromatic rings and epoxy groups.
Highlights
Amidst materials widely used in plastic industry nowadays, thermosets represent about 20% of plastic production [1]
Over 90% of these epoxy materials are based on bis(4-hydroxyphenylene)-2,2-propane, known as bisphenol A (BPA), a petrol-based molecule first synthesized in the 1890s and used as a synthetic oestrogen [5]
To increase the low glass transition temperatures obtained with materials based on glycidylated cardanol, a polyaromatic derivative of it can be designed by a two-steps synthesis, beginning by a phenolation step a
Summary
Amidst materials widely used in plastic industry nowadays, thermosets (or thermosetting polymers) represent about 20% of plastic production [1] They are formed from a liquid or solid mixture of various ingredients including at least one or more monomers. The low glass transition temperature caused by the alkyl chain prevent them from competing with BPA-based materials with their high Tg values and glassy moduli [17]. For this reason, many researches have been devoted to using glycidylated aromatic bio-based materials as substitutes for BPA. Tables gathering all these results will be given at the end of each part for comparative purposes
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