Il brevetto riguarda la preparazione di copolimeri butadiene/isoprene a stereoblocchi mediante catalisi al cobalto.

The polymerization of some 1,3-dienes (i.e., butadiene, isoprene and myrcene) with the catalyst system obtained by combining the imino-pyridine iron complex shown in Figure 1 with methylaluminoxane was examined.1 The polymers were characterized by FT-IR and NMR (1H, 13C and 2D), and were found to exhibit different structure depending on the monomer structure: an essentially syndiotactic 1,2 polymer from butadiene, a predominantly alternating cis-1,4-alt-3,4 polymer containing short cis-1,4 sequences (three units) along the polymer chain from isoprene, and finally an alternating cis-1,4-alt-3,4 polymer containing longer cis-1,4 sequences (five units) along the polymer chain from myrcene, were obtained.

In recent years, the research activity in the field of stereospecific polymerization of conjugated dienes1 has particularly focused on the study of new catalytic systems based on organometallic complexes of transition metals and lanthanides with various types of organic ligands (e.g., phosphines, pyridyl-imines, bis-imines) and with a well-defined structure.2 The results obtained have clearly shown that, at least in principle, each transition metal or lanthanide could be able to provide active and selective catalytic systems for the polymerization of 1,3-dienes once the right combination of metal, ligand and diene monomer was chosen. Following this idea, in the framework of our research work dealing with the synthesis and the characterization of transition metal compounds and the study of their behavior in the polymerization of 1,3-dienes, we have taken into consideration copper. We have in particular examined the polymerization of butadiene, isoprene and myrcene with catalysts obtained by combining bipyridyl and imino-pyridyl copper complexes (see figure alongside) with methylaluminoxane (MAO), exhibiting a quite good activity.3,4 The system (I)/MAO gave a predominantly 1,2 polybutadiene, a crystalline syndiotactic 3,4-polyisoprene (Tm 114°C) and a highly crystalline cis-1,4 poly(2,3-dimethyl-1,3-butadiene) (Tm 198°C); the system (II)/MAO gave from butadiene a slightly crystalline syndiotactic 1,2 polymer; from isoprene a predominantly alternating cis-1,4/3,4 polymer in which however short cis-1,4 sequences (three units) can be detected along the polymer chain, with a Tg value of about -30°C; from myrcene a predominantly alternating cis-1,4/3,4 polymer in which however longer cis-1,4 sequences (five units) are present along the polymer chain, with a Tg value of about -60°C. The results obtained highlight once more the fundamental role played by the ligand structure and the monomer structure on the selectivity in the polymerization of 1,3-dienes. The above complexes, together with the bis-iminopyridyl ones, were also tested for the polymerization of ethylene, obtaining however not very active catalysts.

Several novel cobalt dichloride complexes with amino-phosphine bidentate ligands were synthesized and characterized. For some of them single crystals were obtained and their molecular structure was determined by X-ray diffraction method. All the complexes were then used in combination with MAO for the polymerization of 1,3-butadiene, obtaining polymers with different structures (i.e., predominantly 1,2 or cis-1,4) mainly depending on the type of ligand and on the MAO/Co molar ratio. The behavior of these novel catalysts was compared with that exhibited, in the polymerization of the same monomer, by the systems CoCl2(PR3)2-MAO and CoCl2(PRPh2)2-MAO (R = alkyl or cycloalkyl group), and by the systems based on cobalt dichloride complexes with various bi- and tridentate ligands (e.g., diphosphines, bis-imines, pyridyl-imines, bis-iminopy- ridines). The comparison between the different systems allowed us to make some clarity about the actual and effective role played by the various types of ligands in the polymerization of conjugated dienes with catalytic systems CoCl2(L)-MAO, in which L = mono-, bi-, or tri-dentate ligand.

Some novel copper complexes are synthesized by reacting copper(II) dichloride and copper(II) dibromide with a series of pyridyl-imine ligands differing in the nature of the substituents at the iminic carbon and at the imino nitrogen atom. All the complexes are characterized by analytical and infrared data: for some of them single crystals are obtained, and their molecular structure is determined by X-ray diffraction. The complexes are combined with methylaluminoxane (MAO) for the polymerization of 1,3-dienes (i.e., 1,3-butadiene and isoprene) obtaining active and selective catalysts and, in case of isoprene, polymers with quite unusual structures, i.e., predominantly alternating cis-1,4-alt-3,4 structures containing cis-1,4 units sequences within the polymer chain.

Poly(isoprene)s of different molecular structures have been synthesized with various catalysts based on complexes of Nd-, Co-, and Fe-bearing pyridylimine, phosphine, and bipyridine ligands. Poly(isoprene)s with essentially cis-1,4 structure, 3,4 syndiotactic structure, and regular alternating cis-1,4-alt-3,4 structure have been obtained. Moreover, polymers with an unusual prevalent alternating cis-1,4-alt-3,4 structure but containing cis-1,4 units sequences of different lengths (3 or 5 units) within the chain have also been obtained. The structure and mechanical properties of all of the synthesized poly(isoprene)s, some of them completely new, have been investigated. Poly(isoprene)s with a cis-1,4 structure and with a perfectly alternating cis-1,4-alt-3,4 structure or prevalent alternating cis-1,4-alt-3,4 structure are amorphous, exhibiting mechanical behavior with a viscous flow at relatively high deformation. The sample of poly(isoprene) with almost a regular 3,4 syndiotactic structure (about 79% of 3,4 units) crystallizes in the stable orthorhombic form of 3,4-syndiotactic poly(isoprene). This crystalline sample shows better mechanical properties of deformability and flexibility than the other amorphous poly(isoprene)s without a viscous flow with plastic deformation and breaking at relatively high strain around 300-400% and remarkable elastic properties. The plastic deformation and the elastic behavior are associated with a reversible transformation during tensile deformation of the crystalline orthorhombic form into a disordered mesomorphic form, which recrystallizes into the orthorhombic form upon relaxation during elastic recovery. The glass transition temperature of the different poly(isoprene)s decreases linearly with the increasing cis-1,4 content, from 16 °C of the poly(isoprene) with the prevalent 3,4 structure and 21% of cis-1,4 units to -64 °C of the poly(isoprene) with 98% of cis-1,4 units.

Cobalt catalysts Pyridyl-phosphine ligands Stereospecific polymerization Polybutadiene 1. Introduction Cobalt-based catalytic systems have been extensively investigated since the beginning of the stereospecific polymerization of conjugated dienes thanks to their ability to provide all possible polymers from 1,3-butadiene (cis-1,4; trans-1,4; 1,2) according to the chosen catalytic formulation [1]. Catalysts based on cobalt complexes with mono- dentate, aliphatic and aromatic, phosphines, have been reported to be able to provide poly(1,3-butadiene)s with a highly cis-1,4 structure, highly syndiotactic 1,2 structure or mixed cis-1,4/1,2 structure depending on the nature of the phosphine, thus highlighting a noticeable effect of the ligand on the polymerization selectivity [2-10]; catalysts based on cobalt complexes with bidentate ligands containing N as donor atoms (e.g., pyridyl-imino ligands, bis-imine ligands) were reported to give poly(1,3-butadiene)s with an essentially cis-1,4 structure (>=90 %) regardless of the type of ligand coordinated to the cobalt atom, thereby meaning a negligible effect of the ligand on the polymerization selec- tivity [11-41]. To try to understand the reasons for this diametrically opposite behavior of the above cobalt complexes (i.e., cobalt complexes with * Corresponding author. 1 E-mail address: giovanni.ricci@scitec.cnr.it (G. Ricci). 2 Orcid::http://orcid.org/0000-0001-6977-2920 3 Orcid::http://orcid.org/0000-0003-0161-4963 Orcid::http://orcid.org/0000-0002-5020-5544 https://doi.org/10.1016/j.ica.2023.121424 ABSTRACT New cobalt dichloride complexes with pyridyl-phosphine bidentate ligands were synthesized and characterized. Single crystals were obtained, and their molecular structure was determined by single crystal X-ray diffraction method. The complexes were then used in combination with methylaluminoxane (MAO) for the polymerization of 1,3-butadiene, obtaining predominantly cis-1,4 polymers or with a mixed cis-1,4/1,2 structure depending on the type of ligand and on the MAO/Co molar ratio. A plausible interpretation for this behavior is provided.

Dichloro(2,2?-bipyridine)copper was synthesized by reacting copper dichloride with bypyri- dine, and its behavior, in combination with methylaluminoxane (MAO), in the polymerization of butadiene, isoprene, 2,3-dimethyl-1,3 butadiene, and 3-methyl-1,3-pentadiene was examined. The purpose of this study is to find catalytic systems that are more sustainable than those currently used for the polymerization of butadiene and isoprene (e.g., Co and Ni), but that are comparable in terms of catalytic activity and selectivity. Predominantly, syndiotactic 1,2 polybutadiene, crystalline syn- diotactic 3,4 polyisoprene, crystalline syndiotactic 1,2 poly(3-methyl-1,3-pentadiene), and crystalline cis-1,4 poly(2,3-dimethyl-1,3-butadiene) were obtained in a manner similar to that observed with the analogous iron complex. As far as we know, the investigated catalytic system represents the first example of a copper-based catalyst in the field of stereospecific polymerization. Given the great availability of copper, its extremely low toxicity (and therefore high sustainability), and the similarity of its behavior to that of iron, the result obtained seems to us of considerable interest and worthy of further investigation.

Si tratta di una lezione sulla polimerizzazione stereospecifica dei dieni coniugati, inserita all'interno della Scuola Mario Farina sulla Sintesi di Polimeri, tenutasi a Bertinoro dal 2al 6 maggio 2022.

Il brevetto riguarda la sintesi di copolimeri dienici a stereoblocchi mediante catalisi al cobalto

The fabrication of polyolefin thermoplastic elastomers (P-TPEs) with superior robustness (high strength and high toughness) is challenging. Integrating dynamic (reversible) noncovalent cross-links into P-TPEs may solve the trade-off between strength and toughness and permanent (irreversible) cross-linking and elasticity. Here, we report a two-step synthesis of P-TPEs that contain flexible polymer chains and different thiol branches (less than 2.0 mol %) that cross-link the polymer chains through dynamic hydrogen bonding. The cross-linked polymers exhibit negligible hysteresis after being circularly stretched 10 times at low strain, that is, few dynamic H-bonds break per cycle and delocalize the stress concentration to withstand load and delay premature fracture. At large deformation, the polymers dissipate vast stress energy by the sacrificial H-bond scission: the H-bonds break and reform to prevent failure and to dictate simultaneously high fracture strength (? up to 10.2 MPa) and high toughness (UT up to 22.6 MJ/m3). Meanwhile, the resultant materials present low stiffness (E ? 2.5 MPa), good extensibility (? > 600%), and elastic recovery of 90% even at 680% strain. The cross-linked polyolefins are readily (re)processable, and tensile and elastic properties are largely recovered after being remolded at least twice.

Si tratta di un volume inserito nella serie di "Lezioni di scienza e tecnologia delle macromolecole. La sintesi di polimeri - Scuola AIM 2022" dedicato appunto alla sintesi di polimeri nell'ambito della Suola AIM Mario Farina-2022; il nostro contributo riguarda la polimerizzazione stereospecifica di dieni coniugati

?,?-Dienes are an important class of monomers due to their utility in the synthesis of cyclopolyolefins and reactive polyolefin intermediates. In this contribution, the terpolymerization of two ?,?-dienes (i.e., 1,5-hexadiene and 1,7-octadiene) with ethylene and various cyclic olefins [i.e., norbornene (NB), 5-ethylidene-2-norbornene (ENB), and dicyclopentadiene (DCPD)] catalyzed by a chelated imido vanadium complex has been examined. The ENB and DCPD diene termonomers provide additional sites for post-polymerization functionalization. Vanadium-catalyzed terpolymerization of the investigated ?,?-dienes yields polyolefins with a high molecular weight (Mw up to 200 × 103 g mol-1), unimodal and narrow molecular weight distribution, subambient glass transition temperatures (-30 < Tg °C <-3), and a proper content of C-C bonds. Comprehensive NMR investigation of the obtained polymers revealed that subtle changes in the ?,?-diene size have important effects on the numerous combinations of insertion paths (ring closure vs ring opening), from which different repeating units with a C-C bond in the side or main polymer chain and cyclic units are installed. Finally, the poly(ethylene-ter-1,5-hexadiene-ter-NB) was subjected to thiol-ene addition using thioglycolic acid, methyl thioglycolate, and N-acetyl-l-cysteine to access polar-functionalized polyolefins with a degree of functionalization and properties dependent on the thiol substitution.

Some novel monoalkyl-N-aryl-substituted iminopyridine iron chloride complexes, differing in the nature of the substituent at the iminic carbon and at the ortho position of the aryl ring, were synthesized and characterized. For one of them, single crystals were obtained, which allowed for the determination of its crystalline structure, in which the iron center is coordinated to the chlorides and to the two nitrogen atoms of the ligand. The coordination around iron is distorted tetrahedral, a coordination mode rarely identified for FeCl2 adducts with bidentate nitrogen ligands. All the complexes were used, in combination with methylaluminoxane, for the polymerization of 1,3-butadiene and isoprene, providing syndiotactic 1,2 poly(1,3-butadiene)s and poly(isoprene)s with a predominantly cis-1,4/3,4 alternating structure, in which short cis-1,4 sequences of three or five units, whose length depends on the nature of the ligand on the iron atom, are present. A detailed NMR characterization (1H-, 13C-, and 2D experiments) of the resultant poly(isoprene)s is reported, and a tentative scheme for the formation of the novel isoprene polymers is proposed.

The research on polyolefins focuses on insertion-coordination polymerization catalyzed by molecular transition metal-based catalysts. The major advantage of insertion polymerization is that its mechanism is largely governed by the catalyst structure, which in turn strongly affects the polymer physical and mechanical properties. Amongst the transition metal series, chromium, Group IV and late metal catalysts have been highly reported. [1] Conversely, vanadium complexes have been less investigated as catalyst precursors for olefin polymerization, despite being the catalyst of choice in the production of ethylene-propylene rubber and ethylene-propylene-diene elastomer (EPDM). Herein, we report the synthesis and characterization of a series of imido vanadium(IV) complexes, differing in the ligand substitution, as well as their application in combination with Et2AlCl and Cl3CCO2Et (ETA), in the terpolymerization of ethylene and 5-ethylidene-2-norbornene (ENB) with ?-olefins (e.g. propylene, 1-hexene and 1-octene) (Scheme 1). [2] The resulting polymers have been characterized to study their microstructure, mode of insertion, and thermal properties. Furthermore, the mechanical properties of the obtained EPDMs have been also investigated to evaluate the resistance to strain, the material stiffness and the polymer elasticity. The resulting EPDMs behave as thermoplastic elastomers or soft elastomers, depending on the polymerization conditions and vanadium catalyst employed. Generally, the obtained EPDM thermoplastic elastomers exhibit high elongation at break, strain hardening at large deformation, excellent shape retention properties and remelting processability with no fall in properties for recycle use without the need of polymers blending and reinforcement through the addition of active fillers. Preliminary data about the terpolymerization of ethylene with ENB and ?,?-non conjugated dienes (e.g.1,5-hexadiene and 1,7-octadiene) and subsequent functionalization of the resulting polymers through a radical grafting, will be discussed.

Some novel cobalt diphenylphosphine complexes were synthesized by reacting cobalt(II) chloride with (2-methoxyethyl) diphenylphosphine, (2-methoxyphenyl)diphenylphosphine, and 2- (1,1-dimethylpropyl)-6-(diphenylphosphino)pyridine. Single crystals suitable for X-ray diffraction studies were obtained for the first two complexes, and their crystal structure was determined. The novel compounds were then used in association with methylaluminoxane (MAO) for the polymerization of 1,3-butadiene, and their behavior was compared with that exhibited in the polymerization of the same monomer by the systems CoCl2(PPrPh2)2/MAO and CoCl2(PPh3)2/MAO. Some significant differences were observed depending on the MAO/Co ratio used, and a plausible interpretation for such a different behavior is proposed.

Recently, the research activity in the field of the stereospecific polymerization of conjugated dienes has focused on the use of catalysts based on organometallic complexes having a well-defined structure and containing ligands of various types (e.g., phosphines, bis-imines, and pyridylimines), since it has been observed that the nature of the ligand, as expected on the basis of the diene polymerization mechanism proposed several years ago by Porri, is able to exert a strong influence on the polymerization regio- and stereoselectivity, on the polymer molecular weights and their distribution, and in some cases to impart a living feature to the catalysts themselves. In this Perspective we highlight the most recent results obtained in this field and discuss possible future developments in this area.

Diene-based polymers, specifically cis-1,4 polybutadiene and cis-1,4 polyisoprene, have found and still find main application in the preparation of elastomeric compounds for the production of tires. In order to broaden and diversify the application spectrum of the conjugated diene polymers, it would be desirable to be able to rely on polymeric materials having features different from those of the simple elastomer. The recent discovery and introduction, inspired by Porri's 1,3-dienes polymerization mechanism [1], of a new generation of catalysts based on transition metal and lanthanide complexes having a well defined structure and containing ligands with P and/or N and/or O as donor atoms [2], able to i) afford polymers with different structures from different monomers, ii) exhibit living features, iii) modify their type of selectivity during polymerization while maintaining the living nature, resulted to be extremely useful for this purpose. The strategies adopted to modify the selectivity during the polymerization runs are of different type, ranging from adding a specific ligand to changing the cocatalyst (i.e., different type of aluminum alkyl), from varying the Al/Mt molar ratio to modifying the polymerization temperature. We are reporting in the present communication on two synthetic routes for the synthesis of stereoregular di-block polybutadienes [3] consisting of two stereoregular polymer blocks having different structures and properties: a first block with a highly cis-1,4 structure, amorphous, with a Tg value below -100°C, and a second block with a syndiotactic 1,2 structure, crystalline, with Tm in the range 60-140°C. According to the first synthetic procedure (Figure 1), butadiene is first polymerized with a catalytic system obtained by combining a cobalt complex with ligands (L1) (e.g., PtBu3, PtBu2Me), characterized by a cis-type selectivity, with formation of an amorphous cis-1,4 polybutadiene block. Figure 1. Scheme of formation of stereoregular di-block polybutadienes with cis-1,4/1,2 structure (L1 = PtBu2Me or PtBu3; L2 = PRPh2, R = Me, Et, nPr, iPr, tBu, Cy) 3. Subsequently a second ligand L2 is introduced (generally an aromatic phosphine of the type PRPh2, in which R = alkyl or cycloalkyl group) which replaces L1 on the cobalt atom, causing a drastic change of the catalytic selectivity, from cis-1,4 to syndiotactic 1,2, with the formation of a second block of crystalline polybutadiene with a 1,2 syndiotactic structure (the syndiotacticity degree and therefore the crystallinity vary according to the nature of the R group on the phosphorus atom). Having the initial catalytic system "living features", and being these characteristics maintained even after the addition of the ligand L2, the two polymeric blocks result joined together through a single junction point, thus allowing to have within the same polymer chain the characteristics of both an elastomeric and thermoplastic material, with a considerable advantage for the ultimate properties of the polymer obtained. Completely analogous stereoregular diblock polybutadienes can also be obtained following a second synthetic way, in which butadiene is polymerized with a catalyst obtained by combining a cobalt complex supported by a mixed P&O ligand with MAO; the change in selectivity is in this case obtained by varying the MAO/Co molar ratio during polymerization (Figure 2). Figure 2. Polymerization of 1,3-butadiene with Co(P&O) based catalysts The presence of an oxygen donor atom within the phosphine ligand structure, associated to an increase of the concentration of MAO up to MAO/Co = 1000, likely causes the whole phosphine to migrate on the aluminum atoms, with generation of a cis-1,4 specific catalytic center, quite similar to the one obtained by reacting naked CoCl2 with MAO, a well-known cis-specific catalyst. All the polybutadienes obtained were analyzed by different analytical techniques (FT-IR, NMR, DSC, GPC, RX, AFM, DMA) which clearly supported the effective formation of stereoregular di-block polymers and pointed out the improved properties of these new thermoplastic elastomers with respect to commercial butadiene rubber (BR).

La presentazione vuole rappresentare un ricordo della carriera scientifica dei Prof. Lido Porri e Giuseppe Allegra del Politecnico di Milano, scomparsi nell'autunno del 2019.

L'articolo rappresenta un ricordo dell'attività di ricerca portata avanti nel corso della sua carriera scientifica dal Prof. Lido Porri, scomparso nel novembre 2019