Giuseppe Leone

Living copolymerization of ethylene with 4-methyl-1-pentene by an α-diimine Ni(II)/Et2AlCl catalyst: synthesis of diblock copolymers via sequential monomer addition

Living copolymerization of ethylene (E) with 4-methyl-1-pentene (4M1P) by an α-diimine Ni(II) complex and Et2AlCl as an activator is reported. The living nature of the polymerization was exploited to prepare poly(E-co-4M1P)-block-poly(1-hexene) with low polydispersity index (Mw/Mn ≈ 1.20) and qualitatively good elastomeric properties.

In situ synthesis of fluorescent poly(norbornene)/oxazine-1 dye loaded fluoromica hybrids: supramolecular control over dye arrangement

We report on the in situ synthesis of fluorescent poly(norbornene)/oxazine-1 (Ox1) dye loaded fluoromica mineral Somasif (SME) hybrid materials. SME acts as host for supramolecular arrangement of Ox1 molecules in their 2D interlayer region. The dye arrangement is easily tuned by modulating the dye loading as well as by competitive intercalation with an ammonium surfactant. The dye molecules bend at most by 30° with respect to the SME layer surface increasing the dye loading up to 69% of the clay cation exchange capacity (CEC). This Ox1 state provides accessible interlayer voids which in turn facilitate the entry of polymerizable monomers (i.e., norbornene and ethylene) and the in situgrowth of the polymer. In this way a highly processable polymer hybrid, in which the dye molecules are highly oriented in the inorganic framework, is formed. The optical spectroscopy shows unique J-band characteristics along with the Ox1 monomer features. The formation of the J-aggregates is likely induced by the interlayer segregated poorly polar norbornene phase that forces the Ox1 molecules to increase the head-to-tail interaction between them. These features strongly encourage the technical application of these materials for fabricating functional devices with unique photoluminescence properties.

Ethylene–4-methyl-1-pentene copolymers of complex chain architecture using α-diimine Ni(II) catalysts: synthesis, 13C NMR assignment and understanding the chain-walking mechanism

Ethylene (E) and 4-methyl-1-pentene (4M1P) are copolymerized using an α-diimine Ni(II) catalyst with MAO (methylaluminoxane) or Et2AlCl (diethylaluminium chloride) as the cocatalyst. A series of copolymers with a 4M1P comonomer content ranging from 0.94 to 36.73 mol% are obtained. A detailed 13C NMR assignment is presented and this thorough analysis has opened up the first full description of this interesting family of copolymers. Manifold branched copolymers are obtained with no noticeable differences in the branching distribution by using MAO or Et2AlCl. The resonance assignments are correlated with the chain-walking mechanism: branching analysis shows that the total amount of 2,1 insertion of the comonomer, followed by backward migration of the nickel active species along the polymer chain, is higher than that of 1,2 inserted 4M1P.

Copolymerization of ethylene with α-olefins and cyclic olefins catalyzed by a Ti(IV) diisopropoxy complex bearing a tridentate [O−,S,O−]-type bis(phenolato) ligand

Ethylene (E) was copolymerized with some α-olefins [1-pentene (PEN), 1-hexene (HEX), and 4-methyl-1-pentene (4M1P)] and cyclic olefins [cyclopentene (CPE), norbornene (NB), and dicyclopentadiene (DCPD)] using the Ti(IV) thiobis(phenolate) complex [2,2′-S(4-Me,6-tBuC6H2O)2]Ti(OiPr)2 in combination with methylaluminoxane (MAO). The catalyst exhibited excellent activities (up to 106 g molTi−1 h−1). Crystalline E/α-olefin copolymers with a strong tendency for comonomer alternation were obtained with good comonomer incorporation (about 15 mol% for [Y]/[E] = 8; Y = comonomer) decreasing in the order HEX > PEN > 4M1P. Random copolymers with NB and DCPD were obtained with efficient comonomer incorporation (from 10 to 40 mol%) even for the Y/E molar ratio = 1 to 2, while the catalyst gave poor CPE incorporation. In order to collect information on the comonomer distribution in the copolymers, boiling solvent extraction was carried out and all the fractions were characterized by DSC, XRD, SEC, and NMR.

Encapsulation of a Rhodamine Dye within a Bile Acid Binding Protein: Toward Water Processable Functional Bio Host–Guest Materials

New strategies are requested for the preparation of bioinspired host-guest complexes to be employed in technologically relevant applications, as sensors and optoelectronic devices. We report here a new approach employing a single monomeric protein as host for the strongly fluorescent rhodamine dye. The selected protein, belonging to the intracellular lipid binding protein family, fully encapsulates one rhodamine molecule inside its cavity forming a host-guest complex stabilized by H and π-hydrogen bonds, a salt bridge, and favorable hydrophobic contacts, as revealed by the NMR derived structural model. The protein-dye solutions are easily processable and form homogeneous thin films exhibiting excellent photophysical and morphological properties, as derived from photoluminescence and AFM data. The obtained results represent the proof of concept of the viability of this bio host-guest system for the development of bioinspired optoelectronic devices.

Chirality, entropy and crystallization in polymers: isotactic poly(3-methyl-1-pentene) as an example of influence of chirality and entropy on the crystal structure

We report the synthesis and the crystal structure of isotactic poly((R,S)-3-methyl-1-pentene) (iP(R,S)3MP). A purely random achiral copolymer of two enantiomeric (R) and (S) 3-methyl-1-pentene monomers cannot be obtained by polymerization of the racemic mixture of the (R) and (S) monomers but has been obtained by stereospecific polymerization of 3-methyl-1,3-pentadiene to isotactic 1,2-poly(3-methyl-1,3-pentadiene) (iP3MPD12) and successive hydrogenation. The crystal structures of achiral iP(R,S)3MP and chiral poly((S)-3-methyl-1-pentene) (iP(S)3MP) are different, indicating that crystal structures of polymers may be driven by different entropic effects related to chirality and type of crystal disorder. The conformational disorder of the chiral lateral groups prevails in chiral iP(S)3MP, inducing crystallization of chains of one helical chirality, whereas the entropic effect due to the statistical substitution of chains of different helical chirality in the sites of the lattice prevails in achiral iP(R,S)3MP.

Hierarchically structured, blue-emitting polymer hybrids through surface-initiated nitroxide-mediated polymerization and water templated assembly

A facile and robust approach for fabricating structured, blue-emitting polymer hybrids is explored by grafting poly(styrene) incorporating π-conjugated oligo(fluorene) side-chains, to fluoromica silicate layers through surface-initiated nitroxide-mediated polymerization (SI-NMP). It is expected that the polymer intercalation can effectively reduce π-stacking, chain–chain interactions, twists and bends, and interfacial effects, leading to significant difference in the electronic/optoelectronic properties, and improved optical, thermal and chemical stability of the materials. The experimental results indicate that the bottom-up strategy is rational and efficacious. The hybrids exhibit a blue photoluminescence quantum yield (PL-QY) as high as 0.90, even in the solid, which makes the materials appealing for polymer light-emitting devices (PLEDs). The materials also show significantly enhanced thermal, and chemical stabilities with respect to the organic precursors. If processed under specific controlled conditions, the hybrids spontaneously assemble into highly ordered microporous films, where an organization of matter at different length scales is obtained. Since the introduction of surface patterning in the active layer could enhance the extraction of light generated in the device, this hierarchical organization is a promising tool for the further development of optimized hybrid PLEDs.

Poly(styrene)/oligo(fluorene)-intercalated fluoromica hybrids: synthesis, characterization and self-assembly.

Summary We report on the intercalation of a cationic fluorescent oligo(fluorene) in between the 2D interlayer region of a fluoromica type silicate. The formation of intercalated structures with different fluorophore contents is observed in powders by synchrotron radiation XRD. Successively, the hybrids are dispersed in poly(styrene) through in situ polymerization. Such a procedure allows us to synthesize the materials from solution, to achieve solid films, and to characterize them by optical and morphologic techniques. The polymeric films with homogeneous distribution of the hybrids exhibit ultraviolet–blue photoluminescence with a significantly enhanced photostability compared to the bare oligo(fluorene)s. Finally, under specific conditions, the polymer hybrid with higher oligo(fluorene) content spontaneously assembles into highly ordered microporous films.

Isotactic and Syndiotactic Alternating Ethylene/Propylene Copolymers Obtained Through Non-Catalytic Hydrogenation of Highly Stereoregular cis-1,4 Poly(1,3-diene)s

The homogeneous non-catalytic hydrogenation of cis-1,4 poly(isoprene), isotactic cis-1,4 poly(1,3-pentadiene) and syndiotactic cis-1,4 poly(1,3-pentadiene) with diimide, formed by thermal decomposition of para-toluenesulfonylhydrazide, is examined. Perfectly alternating ethylene/propylene copolymers having different tacticity (i.e., isotactic and syndiotactic), which are difficult to synthesize by stereospecific copolymerization of the corresponding monomers, are obtained. Both isotactic and syndiotactic alternating ethylene/propylene copolymers are amorphous, with very low glass transition temperatures.