Metal-Based Catalysts for Controlled Ring-Opening Polymerization of Macrolactones: High Molecular Weight and Well-Defined Copolymer Architectures

This contribution describes our recent results regarding the metal-catalyzed ring-opening polymerization of pentadecalactone and its copolymerization with ε-caprolactone involving single-site metal complexes based on aluminum, zinc, and calcium. Under the right conditions (i.e., monomer concentration, catalyst type, catalyst/initiator ratio, reaction time, etc.), high molecular weight polypentadecalactone with <i>M</i>_n up to 130 000 g mol^–1 could be obtained. The copolymerization of a mixture of ε-caprolactone and pentadecalactone yielded random copolymers. Zinc and calcium-catalyzed copolymerization using a sequential feed of pentadecalactone followed by ε-caprolactone afforded perfect block copolymers. The blocky structure was retained even for prolonged times at 100 °C after full conversion of the monomers, indicating that transesterification is negligible. On the other hand, in the presence of the aluminum catalyst, the initially formed block copolymers gradually randomized as a result of intra- and intermolecular transesterification reactions. The formation of homopolymers and copolymers with different architectures has been evidenced by HT-SEC chromatography, NMR, DSC and MALDI-ToF-MS

Aluminum Complexes of Bidentate Fluorinated Alkoxy-Imino Ligands: Syntheses, Structures, and Use in Ring-Opening Polymerization of Cyclic Esters

The coordination chemistry of bidentate fluorinated alkoxy-imino ligands onto Al­(III) centers has been studied. The proligands (CF₃)₂C­(OH)­CH₂C­(R¹)N–R² ({ON^R1,R2}­H; R¹ = Me, Ph; R² = Ph, CH₂Ph, cyclohexyl; <b>1a</b>–<b>d</b>) react selectively with AlMe₃ (0.5 or 1.0 equiv) and AlMe₂(O<i>i</i>Pr) or Al­(O<i>i</i>Pr)₃ (0.5 equiv) to give the corresponding monoligand compounds {ON^R1,R2}­AlMe₂ (<b>2a</b>–<b>d</b>) and the bis-ligand compounds {ON^R1,R2}₂AlMe (<b>3a</b>–<b>d</b>) and {ON^R1,R2}₂Al­(O<i>i</i>Pr) (<b>4a</b>–<b>c</b>). X-ray diffraction studies revealed that {ON^Ph,Bn}­AlMe₂ (<b>2a</b>), {ON^Me,Bn}­AlMe₂ (<b>2b</b>), {ON^Me,Bn}₂AlMe (<b>3b</b>), {ON^Ph,Ph}₂AlMe (<b>3c</b>), {ON^Me,Bn}₂Al­(O<i>i</i>Pr) (<b>4b</b>), and {ON^Ph,Ph}₂Al­(O<i>i</i>Pr) (<b>4c</b>) all adopt a mononuclear structure in the solid state; four-coordinate {ON^R1,R2}­AlMe₂ and five-coordinate {ON^Me,Bn}₂Al­(O<i>i</i>Pr) feature respectively distorted-tetrahedral and trigonal-bipyramidal geometries. The ¹H, ¹³C­{¹H}, and ¹⁹F­{¹H} NMR data indicate that the structures observed in the solid state are retained in CD₂Cl₂ or C₆D₆ solution at room temperature. The binary systems {ON^R1,R2}­AlMe₂ (<b>2</b>)/BnOH and discrete {ON^R1,R2}₂Al­(O<i>i</i>Pr) (<b>4</b>) are effective catalysts for the controlled ROP of ε-caprolactone and <i>rac</i>-lactide, both in bulk molten monomer and in toluene solution/slurry. In contrast to the case for {ON^RNO}­Al­(O<i>i</i>Pr), having a bridged tetradentate fluorinated dialkoxy-diimino ligand that provides isotactic-enriched polylactides, the unbridged compounds {ON^R1,R2}₂Al­(O<i>i</i>Pr) (<b>4</b>) produce atactic PLAs. The key element which appears to be at the origin of the absence of stereocontrol is the lack of bridge between the two imino-alkoxy moieties, possibly via a decrease in the rigidity of the compounds and/or a different positioning of N,O vs N,N heteroatoms in axial sites

Aluminum Complexes of Bidentate Fluorinated Alkoxy-Imino Ligands: Syntheses, Structures, and Use in Ring-Opening Polymerization of Cyclic Esters

The coordination chemistry of bidentate fluorinated alkoxy-imino ligands onto Al­(III) centers has been studied. The proligands (CF₃)₂C­(OH)­CH₂C­(R¹)N–R² ({ON^R1,R2}­H; R¹ = Me, Ph; R² = Ph, CH₂Ph, cyclohexyl; <b>1a</b>–<b>d</b>) react selectively with AlMe₃ (0.5 or 1.0 equiv) and AlMe₂(O<i>i</i>Pr) or Al­(O<i>i</i>Pr)₃ (0.5 equiv) to give the corresponding monoligand compounds {ON^R1,R2}­AlMe₂ (<b>2a</b>–<b>d</b>) and the bis-ligand compounds {ON^R1,R2}₂AlMe (<b>3a</b>–<b>d</b>) and {ON^R1,R2}₂Al­(O<i>i</i>Pr) (<b>4a</b>–<b>c</b>). X-ray diffraction studies revealed that {ON^Ph,Bn}­AlMe₂ (<b>2a</b>), {ON^Me,Bn}­AlMe₂ (<b>2b</b>), {ON^Me,Bn}₂AlMe (<b>3b</b>), {ON^Ph,Ph}₂AlMe (<b>3c</b>), {ON^Me,Bn}₂Al­(O<i>i</i>Pr) (<b>4b</b>), and {ON^Ph,Ph}₂Al­(O<i>i</i>Pr) (<b>4c</b>) all adopt a mononuclear structure in the solid state; four-coordinate {ON^R1,R2}­AlMe₂ and five-coordinate {ON^Me,Bn}₂Al­(O<i>i</i>Pr) feature respectively distorted-tetrahedral and trigonal-bipyramidal geometries. The ¹H, ¹³C­{¹H}, and ¹⁹F­{¹H} NMR data indicate that the structures observed in the solid state are retained in CD₂Cl₂ or C₆D₆ solution at room temperature. The binary systems {ON^R1,R2}­AlMe₂ (<b>2</b>)/BnOH and discrete {ON^R1,R2}₂Al­(O<i>i</i>Pr) (<b>4</b>) are effective catalysts for the controlled ROP of ε-caprolactone and <i>rac</i>-lactide, both in bulk molten monomer and in toluene solution/slurry. In contrast to the case for {ON^RNO}­Al­(O<i>i</i>Pr), having a bridged tetradentate fluorinated dialkoxy-diimino ligand that provides isotactic-enriched polylactides, the unbridged compounds {ON^R1,R2}₂Al­(O<i>i</i>Pr) (<b>4</b>) produce atactic PLAs. The key element which appears to be at the origin of the absence of stereocontrol is the lack of bridge between the two imino-alkoxy moieties, possibly via a decrease in the rigidity of the compounds and/or a different positioning of N,O vs N,N heteroatoms in axial sites

Unprecedented Adhesive Performance of Propylene-Based Hydroxyl-Functionalized Terpolymers

The synthesis of hydroxyl-functionalized propylene-based terpolymers and their performance as hot melt adhesives were investigated. The products comprise uniformly distributed butyl and 4-hydroxyl-butyl branches along the polypropylene backbone. Despite the low hydroxyl-functionality level of ≤ 0.5 mol %, hydroxyl-functionalized terpolymers show formidable adhesion to aluminum and steel, providing an adhesive strength exceeding 16 MPa, whereas the nonfunctionalized congeners hardly adhere to these metals. As evidenced by rheological measurements, the functional groups form dynamic crosslinks based on hydrogen bonding and electrostatic interactions with aluminum oxide hydroxide residues, remaining in the product after polymerization. At the industrial application temperature of 180 °C, nondeashed and deashed samples of polymers having 0.1 or 0.5 mol % incorporated 5-hexen-1-ol gave, upon cooling to room temperature, comparable adhesive strengths. Deashing and increasing the functionality level lead to a significant improvement of the adhesion strength at a lower application temperature (130 °C), allowing application of the hydroxyl-functionalized propylene-based terpolymers as high-strength hot melt adhesives for combinations of polypropylene and metals

Toward Polyethylene–Polyester Block and Graft Copolymers with Tunable Polarity

The synthesis and characterization of polyethylene–polyester block and graft copolymers and their potential as compatibilizers in polyethylene-based polymer blends are being described. The various routes to functionalized polyethylenes and the corresponding block/graft copolymers have been compared and evaluated for their scalability to industrial scale production. Hydroxyl chain-end and randomly OH-functionalized HDPE as well as randomly OH-functionalized LLDPE were employed as macroinitiators for producing the corresponding block and graft copolymers. These materials were prepared using two different strategies. The <i>grafting from</i> approach entails catalytic ring-opening polymerization of lactones, i.e., ε-caprolactone and ω-pentadecalactone and hydroxyl-functionalized polyethylenes as macroinitiator. The alternative <i>grafting onto</i> approach involves the preparation of block and graft copolymers via simple and convenient transesterification of polycaprolactone or polypenta­decalactone with OH-functionalized polyethylenes. The copolymers were characterized in terms of their molecular weight (SEC), chemical structure (liquid state NMR), topology (MALDI-ToF-MS), supramolecular assembly (solid state NMR), and thermal properties (DSC analysis). The applied techniques for synthesizing the copolymers allow preparation of the products with sufficiently high molecular weight of the final materials. The copolymers were tested as compatibilizers for polyethylene/polycarbonate blends. As proven by SEM analysis, addition of the compatibilizers resulted in a significant improvement of the blend morphology

Self-Organization of Graft Copolymers and Retortable iPP-Based Nanoporous Films Thereof

Polyolefins might become inexpensive alternatives to the existing membranes based on polyethersulfone. Here, we disclose the production of retortable, well-defined polypropylene (PP)-based nanoporous films derived from amphiphilic graft copolymer precursors. The graft copolymers, containing a polypropylene backbone and polyester grafts, were obtained by grafting lactones, specifically δ-valerolactone and ε-caprolactone, from well-defined randomly functionalized poly(propylene-co-10-undecen-1-ol) as a macroinitiator. Depending on the composition, the graft copolymers self-assemble into droplet, cylindrical, lamellar, or interconnected two-phase morphologies. Functional mesoporous iPP-based films were fabricated by the selective degradation of the polyester blocks of the copolymers. Their structure and morphology were studied using atomic force microscopy (AFM), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), and solid-state NMR, while the mesoporosity was assessed by nitrogen sorption experiments. The pore size of the films is strongly influenced not only by the volume fraction of the copolymer blocks but unexpectedly also by the topology (i.e., number of grafts) of the graft copolymer, as was confirmed by computational modeling studies using the dynamic density functional theory (DDFT) engine within the Culgi software. This work provides a conclusive answer on how the morphology of iPP-based graft copolymers is tuned by the copolymer composition and the amount and length of the grafted polyester blocks. Filtration tests and flux determination demonstrated that such structurally well-defined mesoporous products could be considered for the development of ultrafiltration membranes while the chemical resistance and sterilization tests revealed their robust performance and suitability for water purification applications