Organic-Based Functionalization of Composite Materials as a Case Study to Achieve Materials Innovation

Nowadays, it is almost impossible to imagine an advanced human society without polymer materials, since they probably afford the best balance of mechanical, technical and economical properties among all the materials. At the same time, it is clearly alarming all the side-effects deriving from an excessive and unregulated industrialization, that lead to a “barbarian” plundering of all the priceless materials that the Earth offers us, including plastics and polymers. For this reason, the development of innovative properties in polymer materials has becoming a topic of great interest and many organic chemistry approaches can be effectively developed in order to achieve the desired innovation. In this context, intriguing targets are polymers and polymer-matrix composites because these materials have an exceptional versatility and they find application in an endless list of manufactures and products. One common way to achieve the wanted innovation is to use an adequate additive. Anyhow, some problems could arise from the simple integration of additives in polymers, such as the migration or the incompatibility. An effective way to tackle these problems is to promote a stronger interaction between the polymer matrix and the additive, such as the formation of a covalent bond. Moreover, considering polymer-matrix composites, the heterogeneity of the two distinct phases can lead to different ways of innovations, since it is possible to develop both functionalized fillers or organic additives. Additionally, the polymer matrix is itself another source of possible innovation, since it can be developed to possess an event-triggered (e.g., temperature-triggered) structure that can achieve the desired advanced property. The work herein proposed was carried out in the Prof. Marcantoni’s research group, at the University of Camerino (Italy) with the collaboration of Delta s.r.l. company, from December 2020 to October 2023. The study had the objective to develop innovative properties in polymer-based materials through the use of organic chemistry approaches. Taking into account the photocatalytic activity of TiO2 nanoparticles, in Chapter 1 it is proposed the coating-free functionalization of the surface of polymer materials with titania (TiO2) through the development of a “Safer-by-Design” (SbD) approach. The concept of SbD is related to the reduction of hazardous side-effects linked to the use of nanomaterials, such as the release of nanoparticles. In this way, the development of a photocatalytic pre-polymer enabled both an efficient integration of nanoparticles in polymer materials and a surface migration of the photocatalyst, necessary to achieve the desired innovation. Therefore, polymethylmethacrylate-based composites (PMMA/TiO2 and PMMA/SiO2/TiO2) were effectively produced and the photocatalytic activity of their surfaces tested through the degradation of methylene blue (MB), in accordance to ISO 10678:2010. In this sense, it was observed sufficient photo-activity in prototypes having only 0.45% of TiO2, while greater results were achieved with 0.9%. Moreover, the SEM-EDX analysis confirmed the presence of titanium (Ti) on the surfaces of PMMA/TiO2 and PMMA/SiO2/TiO2 prototypes. In Chapter 2, it is described the development of polyurethane (PU) and polyurethane-acrylate (PUA) materials functionalized with quaternary ammonium salts (QAS). The latter is a common and effective antimicrobial agent and its incorporation in polymer materials is a promising way to achieve antimicrobial polymers. In this way, different approaches were tested. The most promising one was based on the initial quaternization of isoserinol through a stepwise reaction with 1-iododecane and iodomethane. The obtained QASwas effectively characterized through NMR analysis and it was used as a minor component during the synthesis of many PUAs, casting functionalized PUA films. The last work (Chapter 3) was performed during the semester as an exchange PhD student at University of Ghent (Belgium), under the supervision of prof. Winne. In this period, I had the opportunity to study click chemistry approaches with the chemistry and reactivity of triazolinediones (TADs). In this way, the proposed work described a novel reactivity of TAD reagents with activated aryl system, in particular with ortho-hindered-para-substituted phenols. At the beginning, the reactivity was studied with low molecular weight reagents, demonstrating the formation of Alder-ene products at room temperature and using acetonitrile as solvent. In order to (almost) exclusively form the Alder-ene product, it was found as mandatory the presence of an alkyl group (e.g.,methyl) in position 4 and hindered groups (i.e., tert-butyl) in position 2 and 6 of the phenol ring. After these initial experiments, it was explored the reactivity in polymer applications. In this way, a large number of AA-BB copolymers were synthesized. In all cases, the thermo-reversibility of the formed covalent bond was checked through “transclick” reactions. Finally, it was demonstrated the efficiency of Alder-ene adducts to act as thermal-triggered cross-linker in the formation of polymer films starting from natural vegetable oil, generating so new materials starting from renewable feedstock.