How Chain Transfer Leads to a Uniform Polymer Particle Morphology and Prevents Reactor Fouling

The effect of adding diethyl zinc as a chain transfer agent during the polymerization of propylene in heptane performed at 80 degrees C was studied. Although it was expected that the chain transfer would stop after precipitation of the polymer, the polymer molecular weight continued to increase throughout the whole of the polymerization. The presence of diethyl zinc had an additional effect that the polymerizations were devoid of reactor fouling. To unravel this phenomenon, the polymer particle morphology was studied. Under the conditions applied, surprisingly, uniform platelet-shaped polymer particles were formed. At high polymer content, these particles aggregate into microfibrillar structures consisting of nematic columnar strands of the same uniform platelets. The polymer particle morphology, as a result of controlled crystallization, is believed to play a crucial role in preventing reactor fouling

In-Reactor Polypropylene Functionalization-The Influence of Catalyst Structures and Reaction Conditions on the Catalytic Performance

To unravel the relationship between silylene-bridged metallocene catalyst structures and polymerization conditions and their effect on the performance in in-reactor functionalization of polypropylene, the behaviors of rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO, rac-Me2Si(Ind)2ZrCl2, rac-Me2Si(2-Me-4-Ph-Ind)2HfCl2, and rac-Me2Si(Ind)2HfCl2 in propylene/aluminum alkyl-passivated 10-undecen-1-ol copolymerization were compared. Kinetic analysis revealed higher catalytic activities for zirconocenes compared to analogous hafnocenes. Both the zirconocene and hafnocene with substituted indenyl ligands afforded a higher molecular weight capability, improved stereo-selectivity, and enhanced ability to incorporate functionalized comonomers compared to their non-substituted congeners. An in-depth study of polypropylene functionalization using the best performing catalyst system, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO, at temperatures ranging from 40 to 100 °C, revealed a linear inversely proportional correlation of polymerization temperature with functionalized comonomer reactivity (↑Tp → ↓ r1), copolymer molecular weight (↑Tp → ↓Mn), and melting temperature (↑Tp → ↓Tm). While performing well under standard laboratory polymerization conditions, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO showed limited molecular weight and stereo-selectivity capabilities under high-temperature (130-150 °C) solution process conditions. Although immobilization of rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 onto silica, allowing it to be used under industrially relevant slurry and gas-phase conditions, led to an active catalyst, it failed to incorporate any functionalized comonomer

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.</p

Preparation of Well-Compatibilized PP/PC Blends and Foams Thereof

The performance of polypropylene-poly(ethylene brassylate) block and graft copolymers and a polypropylene-polycaprolactone graft copolymer as compatibilizers for polypropylene-rich polypropylene/bisphenol A polycarbonate (PP/PC, 80/20 wt/wt) blends was elucidated. The copolymers were synthesized either by metal-catalyzed ring-opening polymerization or transesterification of a presynthesized polyester, initiated by hydroxyl-functionalized PPs, which themselves were obtained by catalytic routes or reactive extrusion, respectively. Spectroscopic fingerprints of the copolymers from liquid-state nuclear magnetic resonance (NMR) in combination with scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA), and rheology analyses of the blends indicated that the compatibilizers spontaneously organize at the interface of the two immiscible polymers leading to the formation of uniform, stable, nanophase morphologies. The effect of the compatibilizers on the performance of the PP/PC blends was evaluated, and well-compatibilized PP/PC blends showed improved melt strength and strain hardening when compared to pure PP. This was verified by the successful foam extrusion using isobutane as a blowing agent of well-compatibilized PP/PC blends to low-density PP-based foams, for which normally long-chain branched PP is required

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.</p

Nouveaux Complexes Organométalliques à base de Métaux des Groupes 3 et 13 pour la Polymérisation d'Esters Cycliques

(Jury : C. Darcel, N. Avarvari, M. Etienne, R. Gauvin, C. Thomas , J.-F. Carpentier)Thèse de Doctorat de l'Université de Rennes

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 polymn. of pentadecalactone and its copolymn. with e-¿caprolactone involving single-¿site metal complexes based on aluminum, zinc, and calcium. Under the right conditions (i.e., monomer concn., catalyst type, catalyst¿/initiator ratio, reaction time, etc.)¿, high mol. wt. polypentadecalactone with Mn up to 130 000 g mol-¿1 could be obtained. The copolymn. of a mixt. of e-¿caprolactone and pentadecalactone yielded random copolymers. Zinc and calcium-¿catalyzed copolymn. using a sequential feed of pentadecalactone followed by e-¿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 intermol. transesterification reactions. The formation of homopolymers and copolymers with different architectures has been evidenced by HT-¿SEC chromatog., NMR, DSC and MALDI-¿ToF-¿MS

Aluminium coordination complexes in copolymerization reactions of carbon dioxide and epoxides

Al complexes are widely used in a range of polymerization reactions (ROP of cyclic esters and cationic polymerization of alkenes). Since the discovery in 1978 that an Al porphyrin complex could copolymerize propylene oxide with carbon dioxide, Al coordination compounds have been studied extensively as catalysts for epoxide-carbon dioxide copolymerizations. The most widely studied catalysts are Al porphyrin and Al salen derivatives. This is partially due to their ability to act as mechanistic models for more reactive, paramagnetic Cr catalysts. However, this in depth mechanistic understanding could be employed to design more active Al catalysts themselves, which would be beneficial given the wide availability of this metal. Polymerization data (% CO3 linkages, Mn, Mw/Mn and TON) for these complexes are presented and mechanisms discussed. In most cases, especially those employing square-based pyramidal Al complexes, co-catalysts are required to obtain high levels of carbon dioxide incorporation. However, in some cases, the use of co-catalysts inhibits the copolymerization reaction. Lewis acidic Al phenolate complexes have been used as activators in CHO-carbon dioxide copolymerizations to increase TOF and this has recently led to the development of asymmetric copolymerization reactions. Given the ready availability of Al, the robustness of many complexes (e.g. use in immortal polymerizations) and opportunity to prepare block copolymers and other designer materials, Al complexes for copolymerization of carbon dioxide are surely worth a second look

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

International audienceThe coordination chem. of bidentate fluorinated alkoxy-imino ligands onto Al(III) centers was studied. The proligands (CF3)2C(OH)CH2C(R1):NR2 (1, \ONR1,R2\H; R1 = Ph, R2 = Bn (a, Bn = CH2Ph), Ph (c), Cy (d, Cy = cyclohexyl); R1 = Me, R2 = Bn (b)) react selectively with AlMe3 (0.5 or 1.0 equiv) and AlMe2(OiPr) or Al(OiPr)3 (0.5 equiv) to give the corresponding monoligand compds. \ONR1,R2\AlMe2 (2a-d) and the bis-ligand compds. \ONR1,R2\2AlMe (3a-d) and \ONR1,R2\2Al(OiPr) (4a-c). X-ray diffraction studies revealed that \ONPh,Bn\AlMe2 (2a), \ONMe,Bn\AlMe2 (2b), \ONMe,Bn\2AlMe (3b), \ONPh,Ph\2AlMe (3c), \ONMe,Bn\2Al(OiPr) (4b), and \ONPh,Ph\2Al(OiPr) (4c) all adopt a mononuclear structure in the solid state; four-coordinate \ONR1,R2\AlMe2 and five-coordinate \ONR1,R2\2AlMe and \ONR1,R2\2Al(OiPr) feature resp. distorted-tetrahedral and trigonal-bipyramidal geometries. The 1H, 13C\1H\, and 19F\1H\ NMR data indicate that the structures obsd. in the solid state are retained in CD2Cl2 or C6D6 soln. at room temp. The binary systems \ONR1,R2\AlMe2 (2)/BnOH and discrete \ONR1,R2\2Al(OiPr) (4) are effective catalysts for the controlled ROP of ε-caprolactone and rac-lactide, both in bulk molten monomer and in toluene soln./slurry. In contrast to the case of aluminum complexes having a bridged tetradentate fluorinated dialkoxy-diimino ligand that provides isotactic-enriched polylactides, the unbridged compds. \ONR1,R2\2Al(OiPr) (4) 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 compds. and/or a different positioning of N,O vs. N,N heteroatoms in axial sites. [on SciFinder(R)