Titolo della tesi: Renewable feedstocks, applications, and new exchange reactions: a prospective in the field of Covalent Adaptable Networks
Covalent Adaptable Networks (CANs) are a new class of dynamic polymeric materials. CANs possess a cross-linked structure formed by reversible covalent bonds that makes them recyclable and reprocessable (thanks to the dynamicity of the cross-links) with the application of the appropriated stimulus, but at the same time lend them excellent mechanical properties (thanks to the 3D cross-linked network). In this way, CANs possess the finest characteristic of both thermoplastics and thermosets.
This PhD thesis is focused on the preparation of innovative Covalent Adaptable Networks, both employing monomers obtainable from renewable feedstock and both applying new, and never reported, covalent dynamic chemistries. An introduction, containing an analysis and some considerations on the actual situation of the polymeric material field, is reported in Chapter 1.
In the second chapter is reported the first application of the catalyzed transamidation reaction in the preparation of a CAN. A renewable feedstock (oleic acid) has been employed as the starting material for the polymer preparation. The insertion of a catalyst (boric acid) allow the exploitation of the transamination reaction, thus generating a dynamic polymeric material with excellent mechanical and thermal properties, that can be tuned by varying the B(OH)3 content.
In the third chapter it has been tried to merge the preparation of new CANs with the investigation on their possible applications. A series of dynamic polymers, prepared starting from oleic acid and containing aromatic disulfide moieties, have been prepared and characterized. Moreover, their application as polymeric reusable adhesive for metals (copper and aluminum) has been investigated. The tested materials revealed great adhesive properties towards copper and, being fully recyclable, the joint created with these materials could be easily reprocessed with just a slight decrease of the shear strength, thus confirming their possible application as innovative, bio-based, reusable metal adhesive.
In the last chapter a new exchange reaction, that is oxime metathesis, has been reported. The latter, in contrast to imine chemistry, exhibits high hydrolysis resistance. The proposed mechanism is well supported by both experimental and computational studies, and it has been demonstrated the possibility to tune the metathesis reaction rate by changing the substituents attached to the aromatic ring bringing the oxime function. Finally, to demonstrate how this new reaction can be employed as a new dynamic chemistry, a cross-linked dynamic polymeric material, that exploits it to gain the ability to be recycled and reprocessed while maintaining its mechanical properties, has been prepared and characterized.