Laura Boggioni

Influence of the Polymer Microstructure on the Thermal Properties of Cycloolefin Copolymers with High Norbornene Contents

This study involves research on possible relationships between the composition of ethylene/norbornene copolymers and their thermal properties. The copolymers were fully characterised by differential scanning calorimetry (DSC), 13 C NMR spectroscopy, Fourier transformation infra-red (FTIR) and Raman spectroscopy. The results of this study show that there is no linear correlation between the amount of norbornene incorporated in copolymers and thermal behaviour when copolymers containing high norbornene content and different microstructures are considered. The latter of which was found to be extremely sensitive to the catalyst used in its preparation.

Cyclic olefin polymerization and relationships between addition and ring opening metathesis polymerization

Abstract Results of our work concerning: (i) the elucidation of the role of the ionic species [Cp2Ti13CH3]+[Cl·MAO]− and of precursors of alkylidene Cp2TiCH2 species in addition alkene polymerization, (ii) the synthetical strategies for converting the living active titanacyclobutanes into σ-titanocene complexes, and (iii) the evidence for the synthesis of polyethylene polynorbornene di-block copolymer are briefly summarized. 13 C NMR spectra of ethylene–norbornene copolymers, prepared with addition catalysts based on ansa-zirconocenes and methylaluminoxane as cocatalyst, and assignments of comonomer pentads in ethylene–norbornene (EN) copolymers are reported.

Facing Unexpected Reactivity Paths with ZrIV–Pyridylamido Polymerization Catalysts

This work provides original insights to the better understanding of the complex structure-activity relationship of Zr(IV)-pyridylamido-based olefin polymerization catalysts and highlights the importance of the metal-precursor choice (Zr(NMe(2))(4) vs. Zr(Bn)(4)) to prepare precatalysts of unambiguous identity. A temperature-controlled and reversible σ-bond metathesis/protonolysis reaction is found to take place on the Zr(IV)-amido complexes in the 298-383 K temperature range, changing the metal coordination sphere dramatically (from a five-coordinated tris-amido species stabilized by bidentate monoanionic {N,N(-)} ligands to a six-coordinated bis-amido-mono-amino complexes featured by tridentate dianionic {N(-),N,C(-)} ligands). Well-defined neutral Zr(IV)-pyridylamido complexes have been prepared from Zr(Bn)(4) as metal source. Their cationic derivatives [Zr(IV) N(-),N,C(-)}Bn](+)[B(C(6)F(5))(4)](-) have been successfully applied to the room-temperature polymerization of 1-hexene with productivities up to one order of magnitude higher than those reported for the related Hf(IV) state-of-the-art systems. Most importantly, a linear increase of the poly(1-hexene) M(n) values (30-250 kg mol(-1)) has been observed upon catalyst aging. According to that, the major active species (responsible for the increased M(n) polymer values) in the aged catalyst solution, has been identified.

Novel aluminum based cocatalysts for metallocene catalyzed olefin polymerization

Abstract The ethylene polymerization activity of rac -Et(indenyl) 2 ZrCl 2 /AlR 3 /modifier was studied. Modifiers were added to β-branched trialkylaluminum Al( i -Bu) 3 (TIBA), and Al( i -Oct) 3 (TIOA), and to their aluminoxanes, TIBAO and TIOAO, respectively, with the aim of obtaining new cocatalysts that operate at low aluminum/transition metal ratios. The modifiers selected contain hetero-atoms and aryl or alkyl groups bearing electron withdrawing substituents or sterically encumbered groups: C 6 F 5 OH, C 6 Cl 5 OH, C 6 F 4 (OH) 2 C 6 F 5 NH 2 , 2,5-(C 6 H 5 ) 2 C 6 H 3 OH, (CF 3 ) 2 CHOH. The in situ reaction between aluminum compounds and modifiers such as C 6 F 5 OH yields new modified aluminum alkyl and aluminoxane cocatalysts bearing one alkoxy or aryloxy group. The simultaneous effect of electron withdrawing substituents on the aryloxy group and of steric hindrance due to β-alkyl substituted alkyls on aluminum leads to good activation of metallocenes at Al/Zr molar ratios as low as 200/1, in conditions in which methylaluminoxane and β-branched alkylaluminoxanes are inactive. NMR studies of the reactions between C 5 Me 5 ZrCl 2 with TIOA, TIOA/C 6 F 5 OH, TIOAO and TIOAO/C 6 F 5 OH demonstrated that in contrast to TIOAO-C 6 F 5 OH, TIOA-C 6 F 5 OH allows the formation of an active alkylated ion pair, thus qualitatively allowing us to understand the polymerization activity of C 5 Me 5 ZrCl 2 based systems.

Late-Transition Metal Complexes with Mixed NO, NS, NP Chelating Ligands for Olefin Polymerization Catalysis

Mixed chelating ligands which contain a nitrogen donor atom in combination with P, O, or S are a novel class of frameworks for generating complexes of unusual reactivity. Complexes of group X metals (Ni and Pd) supported by these ligands are currently exploited as homogeneous catalysts for: olefin polymerization, copolymerization of olefins with functionalized monomers, olefin polymerization in uncommon solvent such as water. This chapter covers the literature on the subject.

Silyl-Terminated Ethylene-co-Norbornene Copolymers by Organotitanium-Based Catalysts

Ethylene (E) and norbornene (N) were copolymerized in the presence of PhSiH(3) as chain-transfer agent with [Ti(η(5) :η(1) -C(5) Me(4) SiMe(2) NBu(t) )(η(1) -Me)(2) ] precatalyst combined with [Ph(3) C][B(C(6) F(5) )(4) ]. The silane was introduced at chain-ends of E-co-N copolymers with concomitant reinitiation of the growing polymer chain. The concentrations of the silane and polymer molecular weight are inversely correlated. The characteristic signals of SiH(2) Ph chain-ends were observed by (1) H NMR. The Si heteroatom is predominantly adjacent to ethylene units in E-co-N copolymers with high N content.

Polyolefins with Cyclic Comonomers

Highly active metallocenes and other single-site catalysts have opened up the possibility to polymerize cycloolefins or to copolymerize them with ethene or propene. The polymers obtained show interesting structures and properties. The cycloolefins such as cyclopentene, norbornene, and their substituted derivatives are incorporated into the polymer chain either by addition or metathesis. An overview of copolymers obtained via addition copolymerization is here given. Materials with elastomeric properties or tactic polymers with high glass transitions and melting points can be obtained, depending on the wide range of different microstructures. Cycloolefin copolymers and homo- and copolymers of norbornene, in particula, are of great academic and industrial interest because of their properties and applications in optoelectronics, lenses, and coatings.

Copolymer Microstructures of Ethylene Norbornene Copolymers Prepared with Homogeneous Metallocene Based Catalysts

Series of ethylene-norbornene copolymers were synthesized in the presence of zirconocenes with different symmetries and ligand patterns and at different norbornene/ethylene ratios. Copolymers were characterized by 13C NMR spectroscopy; Inadequate NMR sequences were used also. The comparison of 13C NMR spectra of copolymers prepared with different norbornene content and the correlation between 13C NMR chemical shifts and conformational structures of the chain on the basis of molecular mechanics calculations were performed. Preliminary assignments were revised and new comonomer sequences such as ENNE which contain meso and racemo NN dyads were assigned.

Propene Polymerization with C1-Symmetric Fluorenyl-Metallocene Catalysts

Propene homopolymers have been produced by employing three C1-symmetric metallocene molecules (1, 2 and 3), each having t-butyl substituent(s) on the Cp, on the fluorenyl or on both aromatic moieties activated with methylaluminoxane at different polymerization temperatures and monomer concentrations. Polymers’ microstructures determined by 13C NMR spectroscopy suggest that the otherwise dominant alternating mechanism governed by the chain migratory insertion is largely replaced by the competing site epimerization mechanism, as a direct result of the imposing steric bulk of the t-butyl substituent on one of the distal positions of the Cp moiety. This phenomenon is more pronounced with 3 when a second t-butyl is present in the same half-space of the molecule making the site epimerization mandatory. The lower activity of catalyst 3 with respect to catalyst 2 is also in line with the necessity for the polymer chain to back-skip (or the site to epimerize) to its original position before the subsequent monomer insertion. Chain end group analyses by 1H NMR spectroscopy have revealed that the formation of vinylidene end groups, either via β-H elimination or as a result of direct chain transfer to the monomer after an ordinary 1,2-insertion is the prevailing chain termination route. A correlation between the relative concentrations of vinylidene end groups of polypropene (PP) polymers produced with each catalyst and the corresponding polypropenes’ molar masses was found, indicating the lower the relative concentrations of vinylidene end groups, the higher the molar masses.

Terpolymerization of Substituted Cycloolefin with Ethylene and Norbornene by Transition Metal Catalyst

Ethylene-norbornene terpolymerization experiments using 5-alkyl-substituted norbornenes (5-pentyl-2-norbornene (C5N) and 5-octyl-2-norbornene (C8N)) or dicyclopentadiene (DCPD) were conducted with two ansa-metallocenes, [Zr{(η5-C9H6)2C2H4}Cl2] (1) and [Zr{(η5-2,5-Me2C5H2)2CHEt}Cl2] (2), activated by methylaluminoxane (MAO). The terpolymers obtained were investigated in detail by determining the microstructure and termonomer contents by 13C NMR, molar masses and thermal properties. Results were compared to those of ethylene (E)-norbornene (N) terpolymerizations with 1-octene. 2, with lower steric hindrance and a shorter bridge, gave the best activities, termonomer incorporation and molar masses. The size of the substituent in 5-alkyl substituted norbornene also plays a role. C8N gives the highest activities and molar masses, while DCPD terpolymers have the highest cycloolefin content. Terpolymers are random; their molar masses, much higher than those in 1-octene terpolymers, are in a range useful for industrial applications. Finally, Tg values up to 152 °C were obtained. For similar N content, poly(E-ter-N-ter-C8N)s and poly(E-ter-N-ter-DCPD)s have the lowest and the highest Tg values, respectively. Thus, the presence of an eight-carbon atom pendant chain in C8N increases the flexibility of the polymer chain more than a five-carbon atom pendant chain in C5N. The higher rigidity of C5N may lead to lower activities and to increasing probability of σ-bond metathesis and chain termination, as evidenced by chain-end group analysis.