Marzocchi, Raffaele (2026) Sustainable polymeric materials from renewable biomass with tailored properties. [Tesi di dottorato]

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Abstract

The aim of the present PhD work is the study of polymeric materials with low environmental impact, obtained from biobased monomers. The main objective was to systematically understand structure–property relationships and to evaluate the possibility of replacing fossil-based materials with sustainable alternatives, while maintaining or, where possible, improving the functional performance of the final materials. The study examined homo and co-polymers derived from biomass, focusing on how synthesis conditions, composition, and macromolecular architecture influence the properties of the final materials. The ability to modulate polymer composition and architecture enabled the development of materials covering a wide range of application sectors, spanning from potential elastomers to plastic or glassy materials. This research involved close collaboration with national and international universities, leading to the publication of several scientific contributions. In particular, in collaboration with the University of Salerno, structure–property relationships of homo- and co-polymers of terpene- and terpene derivatives obtained through titanium-based [OSSO]-type catalytic systems were investigated. In this context, the effect of ligand steric hindrance on the resulting chain microstructures was also analyzed. With the same university, structure–property relationships of copolymers obtained by ring opening copolymerization of different epoxides with cyclic anhydrides, and CO₂ were also studied. At the international level, collaboration was carried out with the University of Lille, where copolymers of S,S-lactide (LA) and ε-caprolactone (CL) were synthesized using different strategies, and subsequently characterized for their properties. The polymer species studied in this thesis can be classified into five main categories, each discussed in a dedicated chapter. In Chapter 3, hybrid β-myrcene–styrene (MS) and β-ocimene–styrene (OS) copolymers, were investigated. The studied copolymers were multiblock materials combining aromatic rigidity with terpene flexibility, allowing control of thermomechanical properties through stereoregularity and regiospecificity. Copolymerizations were performed using a MAO-activated titanium-based catalysts, yielding samples with variable M/S or O/S ratios. These materials exhibited phase separation due to the low miscibility of terpene and S sequences, resulting in the formation of soft terpene-rich domains and hard styrene-rich domains. This heterogeneous morphology developed on length scales of 10–40 nm. The obtained materials showed potential for surface-coating applications owing to their tunable rigidity, elasticity, and thermal stability. In Chapter 4, a terpene-derived monomer S-4-isopropenyl-1-vinyl-1-cyclohexene (IVC), was polymerized via 3,4 insertions, yielding highly isotactic poly(S-4-isopropenyl-1-vinyl-1-cyclohexene) (PIVC). A structurally related polymer, poly(vinylcyclohexene) (PVCH), was also studied. They were synthesized using [OSSO]-type titanium complexes which enabled high regio- and stereoselectivity. Both polymers were amorphous and brittle, and were not able to crystallize from the melt, even after thermal annealing treatments, despite their high regio- and stereoregularity. However, poly(vinylcyclohexane) obtained upon hydrogenation of PVCH was highly crystalline, with a melting temperature of ≈ 300 °C, confirming the high isotactic configuration of the precursor polymer. To broaden the potential applications, IVC was also copolymerized with two terpenes, M and O, yielding fully biobased copolymers whose properties strongly depended on the terpene content incorporated into the polymer chain. In Chapter 5, the monomer 1-phenyl-1,3-butadiene (1PB), derived from cinnamaldehyde, was employed to synthesize poly(1-phenyl-1,3-butadiene) (PPB), using a MAO-activated [OSSO]-type titanium catalysts. The process led to highly isotactic (mmmm > 99%) and regio-regular polymer characterized by 3,4-insetions. The resulting PPB was amorphous and its glass transition temperature Tg decreased from approximately 80 °C to 17 °C upon hydrogenation, highlighting the role of side groups saturation in enhancing chain flexibility. Multiblock copolymers of 1PB with terpenes such as O and IVC were also studied. Some of these materials exhibited two Tgs values, higher than those of the corresponding homopolymers, as a consequence of partial cross-linking reactions. In 1PB/O copolymers, the Tg value decreased as ocimene content increased, whereas in PPBI samples, due to the similar Tg values of the two homopolymers, this remained nearly unchanged. Copolymers of LA and CL were investigated in Chapter 6. They were synthesized resorting to Chain-Shuttling Polymerization (CSP) technology and to single catalytic systems. Copolymers obtained via CSP, with two different amino(bis)phenolate supported aluminium complexes, were semicrystalline after synthesis, with LA sequences crystallizing in the α-form. However, these sequences were unable to crystallize by cooling the melt, due to slow crystallization kinetics, but underwent cold-crystallization upon aging at room temperature or annealing at temperatures above the glass transition temperature. Furthermore, these LA/CL copolymers exhibited macro- and meso-phase separated morphologies due to the low miscibility of LA-rich and CL-rich sequences. In the same chapter, copolymers obtained using a single catalytic system were also studied. Copolymers with different composition were synthesized by employing two different catalysts, an amino(bis)phenolate supported aluminium complex and aluminum isopropoxide, adopting different copolymerization strategies. These copolymers were also semicrystalline, with the crystalline phase corresponding to the α-form of PLLA. All copolymers, regardless of the adopted synthetic route, exhibited mechanical properties markedly superior to those of PLLA, effectively overcoming the severe brittleness of the homopolymer. Finally, in Chapter 7, a library of polyester-polycarbonate (PCPE) copolymers was investigated. These materials were derived from ring-opening copolymerization (ROCOP) of epoxides such as cyclohexene oxide (CHO), vinylcyclohexene oxide (VCHO) and propylene oxide (PO), with CO2 and cyclic anhydrides such as phthalic anhydride (PA) and diglycolic anhydride (DGA), using catalytic systems based on di-nuclear complexes of the [OSSO] type. All these terpolymers were amorphous and brittle, except for the PCPE sample obtained from ROCOP reaction of propylene oxide (PO) with diglycolic anhydride (DGA) and CO₂, that showed a low Tg. In summary, the thesis consolidates fundamental advances in sequence-controlled polymerization, as well as in the understanding of structure, morphology, mechanical properties, and thermal behavior of polymer species derived from biomass. Furthermore, it translates these advances into techno-relevant outcomes such as improved ductility compared to neat PLLA, expanded service-temperature windows through hydrogenation, development of materials with a broad range of properties, and the design of recyclable PCPE platforms. Together, these contributions chart a path for rationally engineered, biobased polymers that meet application requirements today while enabling circularity and reduced environmental burden.

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