Synthesis and application of epoxy based vitrimers using renewable resources as feedstocks

Cheng Hao

doi:10.7273/000004224

Epoxy based thermosetting polymers have been widely used in various applications, such as adhesives, coatings and composite materials. Current epoxy materials are constructed by permanent and covalent bonds, which make their repairing and recycle difficult. In addition, more than 75% of commercial epoxy resins are derived from petroleum-based bisphenol A which is nonrenewable and has some health concerns. To address these issues, the aim of this thesis is to develop repairable and recyclable epoxy polymer materials using renewable feedstocks as feedstocks. In the recent ten years, vitrimers have just emerged as a new type of polymers. The dynamic covalent bonds in vitrimers impart reparability to the materials without damaging the integrity and mechanical properties. In this work, we employed the vitrimer chemistry in material preparation and developed two types of repairable epoxy materials using renewable feedstocks. The main contents of this thesis research are described as follows. (1) An eugenol based vitrimer with high glass transition temperature (Tg) was prepared. Eugenol and 4,4′-bis(chloromethyl)-1,1′-biphenyl was used to synthesize a eugenol epoxy compound with a stiff backbone. After this compound was cured with succinic anhydride, the resulting crosslinked polymers exhibited fast stress relaxation at high temperatures (> 160 °C) due to the thermally induced dynamic transesterification. The damaged materials could be repaired with a recovery up to 83 % in 120 min. In addition, the cured epoxy materials also displayed excellent shape memory property. This work demonstrates a promising method for producing high performance vitrimers from renewable chemicals. (2) A biobased vitrimer with high lignin-content was introduced. Kraft lignin was chemically modified using an anhydride to improve its reactivity and compatibility with organic compounds. The modified lignin, which had a significant amount of carboxyl groups, was used to react with an epoxy compound based on diglycidyl ether of poly(ethylene glycol) to prepare an epoxy/carboxylic acid vitrimer system. The cured materials exhibited a uniform phase structure without phase separation noted even at a high loading level of lignin (63 wt%). The dynamic transesterification reaction at high temperatures resulted in rapid stress relaxation and offered excellent self-healing property to the materials. In addition, use of this lignin-based vitrimer as a high-performance metal coating resin was demonstrated. This research work integrates the concepts of biobased (eugenol and lignin) polymers and vitrimer chemistry, and develop two biobased vitrimer materials with high bio-contents.

Synthesis and application of epoxy based vitrimers using renewable resources as feedstocks

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