Recent Studies on Single Site Metal Alkoxide Complexes as Catalysts for Ring Opening Polymerization of Cyclic Compounds

Cellulose nanocrystal-based synthetic biodegradable biopolymeric composites: A comprehensive review on recent progress

With the worldwide transformation to a circular and low-carbon economy, the demand for sustainable materials has skyrocketed in recent years. Of various methods, sustainable and biodegradable biopolymers derived from renewable bioresources have received significant interest. Synthetic biodegradable biopolymers offer tremendous advantages over natural biodegradable biopolymers due to their stability, flexibility, and a wide range of achievable properties to fit several applications. However, the widespread adoption of synthetic biodegradable polymers in high-performance applications is limited by shortcomings in their functional properties. Researchers are actively working to enhance the properties of these materials. A potential solution to improve the performance of biopolymers is to reinforce them with cellulose nanocrystals (CNCs). This review delves into the inclusion of CNCs into synthetic biodegradable biopolymer blends, examining their impact on the mechanical, thermal, morphological, rheological, and barrier properties. Surface modification of CNCs promotes a uniform distribution and strong bonding with the polymer matrix which is pivotal to unlocking their outstanding properties. Moreover, this review highlights the promising potential of CNCs to enhance the performance of synthetic biodegradable composites for a more sustainable future, particularly in packaging applications.

Eco-Friendly and Ready-To-Market Polyurethanes: A Design of Experiment-Guided Substitution of Toxic Catalyst and Fossil-Based Isocyanate

In this contribution, we tackle the replacement of the Hg-based catalyst and fossil-derived isocyanate precursors toward the formulation of a more sustainable polyurethane thermosetting resins (PUs), emulating the performance of a fully fossil-based one employed in industrial encapsulation of optoelectronics. A mixed Bi-Zn catalyst and a 71 % bio-based isocyanate are exploited at this aim through multivariate chemometric approaches, namely Design of Experiment (DoE). DoE allows us to investigate the effect of different formulation factors on selected parameters, such as the film flexibility and transparency or the gel time. More in detail, it is found that a low amount of Zn-rich catalytic mixture leads to a ready-to-market polyurethane only when a fossil-based isocyanate is used. Differently, PUs formulated with bio-based isocyanate, albeit showing a higher bio-based content, present an insufficient optical purity, jeopardizing their market acceptability. Nevertheless, adding a negligible amount of a specific long chain fatty acid as reactivity modulator in the formulation leads to a bubbles-free and ready-to-market resin showing an impressive 65 % w/w content of circular and bio-based components.

Recent Advances in the Titanium-Based Catalysts for Ring-Opening Polymerization

At present, economic development and daily life cannot be separated from organic synthetic polymers. However, a large number of nondegradable polymers have caused serious pollution to the environment. It is necessary for sustainable development to use biodegradable materials instead of traditional polymers, but it is not yet comparable in performance and cost to the competitor it will replace. Therefore, there is a long way to go to develop effective synthesis methods. Through ring-opening polymerization, some cyclic monomers, such as ε-caprolactone or lactide, can be synthesized into biodegradable polymers, which can not only replace traditional synthetic polymers in some fields but also have applications in drug delivery, surgical consumables, human implant materials, bone materials, etc. Ring-opening polymerization is a potential candidate for solving environmental pollution. For ring-opening polymerization, catalysts are very important, among which titanium catalysts have attracted much attention because of their high efficiency, economy, and nontoxicity. In this paper, the development status of organotitanium compounds as ring-opening polymerization catalysts is reviewed, including the effects of different ligand structures on polymerization behavior and polymer structure, and its development trend is prospected. We hope that this review will be helpful for developing efficient ring-opening polymerization catalysts.

Fabrication of Mildew-Resistant Wood with Multi-Functional Properties Based on In Situ Growth of Metal-Organic Frameworks

Wood is easily affected by decay fungi, mildew fungi, insects, water, UV, and other factors when used outdoors. In particular, mildew on the surface of wood negatively affects the appearance and practical use of wood or wood-based engineered products. In recent years, as a class of popular crystalline materials, metal-organic frameworks (MOFs) have been widely applied in electrochemistry, adsorption, anti-mildew efforts, and other areas. In this study, we first grew a Co-based metal-organic framework (Co-MOF) in situ on a wood surface and subsequently converted the Co-MOF in situ into a cobalt-nickel double hydroxide layer, which formed micro- and nanohierarchical composite structures on the wood surface. The low surface energy of the CoNi-DH@wood was further modified via impregnation with sodium laurate to obtain the superhydrophobic wood (CoNi-DH-La@wood). We characterized the microstructure, chemical composition, water contact angle, and anti-mold properties of the CoNi-DH-La@wood using SEM, XRD, XPS, water contact angle tests, and anti-fungal tests. The SEM, XRD, and XPS results confirmed that the metal-organic framework was coated on the wood surface, with the long-chain sodium laurate grafted onto it. The CoNi-DH-La@wood had a water contact angle of 151°, demonstrating excellent self-cleaning ability. In addition, the fabricated superhydrophobic balsa wood exhibited excellent chemical and environment stability. Lastly, the CoNi-DH-La@wood exhibited excellent anti-mildew properties in a 30-day anti-mildew test because the superhydrophobic coating was successfully coated on the wood surface. In summary, this work presents an attractive strategy for obtaining wood with superhydrophobic properties at room temperature, thereby endowing the wood or wood-based engineered products with excellent anti-mildew properties.

Highly Active Homoleptic Zinc and Magnesium Complexes Supported by Constrained Reduced Schiff Base Ligands for the Ring-Opening Polymerization of Lactide

New homoleptic zinc and magnesium complexes containing constrained reduced Schiff base ligands based on substituted 7-hydroxy-1-indanone were successfully synthesized and used as a catalyst for the polymerization of lactide. The ligands contain a side arm having different basicity because dimethylamino, pyridyl, and furfuryl groups are shown to greatly affect the polymerization rates. The homoleptic zinc complex containing constrained reduced Schiff base ligands and a dimethylamino side arm was highly active, giving a 92% conversion of l-lactide in 3 min using [LA]:[Zn]:[BnOH] = 500:1:2 at room temperature. The polymerization is pseudo-first-order dependent on the LA concentration. Well-controlled and living behavior of the zinc complex was observed and demonstrated in the preparation of stereodiblock and triblock copolymers of l-, d-, and rac-lactide in a one-pot sequential synthesis with a predictable block length, block sequence, and narrow dispersity rapidly in 10 min. Stereocomplex formation was observed for PLA made sequentially from 100 l-LA, 100 rac-LA, and 100 d-LA having a high T_m of up to 220 °C.

Unique reactivity of an α-ketiminopyridine ligand with metal–alkyls: Synthesis and ROP of ε-caprolactone

The reaction of an α-ketimininopyridine ligand 2-((Me)CN(C₆H₃-2,6-iPr₂))-6-(OMe)C₅H₃N (L¹) with metal–alkyls, such as MeLi, Et₂Zn, Me₃Al and Me₂AlCl, was studied.