UV-activated thiol-limonene reactions to afford novel polyvinyl butyral based polymeric networks

The urgent quest for environmental sustainability has intensified the search for innovative strategies for the development of advanced materials and novel bio-based polymers. Polyvinyl butyral (PVB), a copolymer used in laminated safety glass, is a valuable target for alternative applications. A novel approach to PVB repurposing was developed, using limonene, a renewable terpene from citrus fruits, as a sustainable monomer in thiol-ene reactions. Poly(thioether-co-limonene) copolymers were synthesized via one-pot thiol-ene reactions using either linear 1,6-hexanedithiol and 2,2’-(ethylenedioxy)diethanethiol), or multifunctional thiols, such as pentaerythritol tetrakis(3-mercaptopropionate and trimethylpropane tris(3-mercaptopropionate). UV light-promoted and thermally-promoted thiol-ene reactions were conducted by using several initiators (benzoyl peroxide, 2,2′-azobis(2-methylpropionitrile) or 2,2′-dimethoxy-2-phenylacetophenone). The use of multifunctional thiols allowed the synthesis of crosslinked polymer networks. In the presence of PVB, semi-interpenetrating polymer networks were obtained with various amounts of PVB (0, 1, 5, and 10 % wt), characterized by FT-IR spectroscopy. The mechanical properties of the polymeric materials were modulated by the thiol structure and by the PVB content. Ultraviolet (UV-A and UV-B) blocking efficiency and ultra-protection factor (UPF) were assessed and showed a correlation with the network structure and PVB composition.