Three dinuclear aluminum alkyl complexes of the general formula LAl₂Me₄, where L are salen ligands with an alkyl backbone of different lengths between the nitrogen atoms (1,3-propylene (1), 1,5-pentylene (2) and 1,12-dodecaylene (3)), have been prepared through alkane elimination reactions between each ligand and two equivalents of AlMe₃. The related hemi-salen aluminum complex 4 was prepared by an analogous reaction between a phenoxy–imine ligand and a single equivalent of AlMe₃. The activities of these aluminum complexes in the ring-opening polymerization (ROP) of rac-lactide and of several epoxides have been investigated and compared. The dinuclear complex 1, bearing the salen ligand with the shortest alkyl bridge, was the most active in the ROP of LA producing isotactic enriched PLA. Otherwise, the other complexes (2 and 3), in which the metal centers are remote, produced atactic PLA with inferior activity. Analogous differences in terms of activity emerged in the ROP of epoxides. The comparison of the catalytic behavior of the dinuclear complexes as well as their mononuclear counterparts suggests the cooperation between the two aluminum metal centers of the dinuclear species in which these are close enough.

A bimetallic salen aluminum complex (1), where salen is N,N-bis(4,6-di-tert-butyl salicylaldimine)-1,3-propylendiamine, was tested as a catalyst for the ring opening polymerization (ROP) and copolymerization (ROCOP) of cyclic esters, such as L-lactide (L-LA), ε-caprolactone (ε-CL), and β-butyrolactone (β-BL) with different heterocyclic substrates, such as cyclohexene oxide (CHO) and succinic anhydride (SA). Copolymers ranging from gradient to blocky structures were obtained from the copolymerization of the different couples of lactones. In the copolymerization of CHO with a cyclic ester, block polyether-co-polyesters were prepared by sequential monomer addition while polyesters were obtained, as exclusive products, when both monomers were simultaneously present in the reaction medium. From a mixture of three different monomers: CHO, SA and a cyclic ester, block copolyesters derived from two different catalytic processes, ROCOP of CHO/SA followed by ROP of the lactone, were instead produced. Surprisingly, a perfect selectivity was observed in the CHO/SA copolymerization without any addition of a cocatalyst; this suggested that the lactone comonomer could act as an endogen cocatalyst.

A series of dimethyl aluminum complexes of the type [E,O]AlMe₂ stabilized by phenoxy-imine, phenoxy-thioether and phenoxy-amine ligands have been tested as catalysts for the ring-opening copolymerization of epoxides and anhydrides. All complexes revealed to be active in the copolymerization of cyclohexene oxide with succinic anhydride showing activities higher than pentacoordinate salen aluminum complexes. Interestingly, these complexes revealed to be active in the copolymerization of limonene oxide with phthalic anhydride. A moderate influence of the ligand structure on the efficiency and selectivity of the catalyst was also observed. Some mechanistic insights have been gained through NMR studies allowing the identification of a zwitterionic species formed in the initiating step of the polymerization reaction.

The growing interest in sustainable additive manufacturing has driven research into customized biocomposite filaments reinforced with natural fibers. This study evaluates the influence of flax fiber content (5–15 wt%) on the thermal, rheological, morphological, and mechanical properties of fully bio-based polyamide PA10.10 filaments intended for fused deposition modeling (FDM). Filaments containing up to 15 wt% flax fibers were produced using both conventional single-screw extrusion and the METEOR^® elongational mixer to compare shear- and elongation-dominated dispersive mechanisms. Increasing flax loading enhanced stiffness (up to +84% tensile modulus at 15 wt%) but also significantly increased porosity, particularly in METEOR-processed materials, leading to reduced strength and intrinsic viscosity. Microscopy confirmed fiber shortening during compounding and revealed porosity arising from moisture release and insufficient fiber wetting. Rheological analysis showed the onset of a pseudo-percolated fiber network from 10 wt%, while excessive porosity at higher loadings impeded melt flow and printability. Based on the combined evaluation of the mechanical performance, dimensional stability, and processability, a 5 wt% flax formulation was identified as the optimal compromise for FDM. A functional automotive demonstrator (Fiat 500 dashboard fascia) was successfully printed using optimized FDM parameters (nozzle 240 °C, bed 75 °C, speed 20 mm s⁻¹, 0.6 mm nozzle, 0.20 mm layer height, and 100% infill). The part exhibited controlled shrinkage and limited warpage (maximum 1.8 mm across a 165 × 180 × 45 mm geometry with a 3 mm wall thickness). Dimensional accuracy remained within ±0.7 mm relative to the CAD geometry. These results confirm the suitability of PA10.10/flax biocomposites for sustainable, lightweight automotive components and provide key structure–processing–property relationships supporting the development of next-generation bio-based FDM feedstocks.