Polypropylene reactor mixture obtained with homogeneous and supported catalysts

Propylene polymerizations were performed with homogeneous ?₂C(Flu)(Cp)ZrCl₂ and SiMe₂(Ind)₂ZrCl₂ catalyst mixtures and with mixtures supported on the zeolite acid mordenite. The polymerizations were performed in toluene and hexane/triisobutylaluminum at different temperatures and Al(MAO)/Zr concentration ratios. The effects of these variables on the catalyst activity were investigated with statistical experimental planning. The average molecular weights, molecular weight distributions, melting temperatures, and crystallinities of the obtained polymers were examined. The results showed lower activities for the homogeneous catalyst mixture than for the isolated systems. On the other hand, high activities were obtained for the syndiospecific heterogeneous system, but very low values were obtained for the supported isospecific metallocene, although both catalysts were prepared under the same conditions. The supported binary system showed intermediary catalyst activity in comparison with the syndiospecific and isospecific supported catalysts. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 263–272, 2005     

Polypropylene fractions produced by binary metallocene catalysts

Because of the great economic interest in propylene‐based polymers and the possibility of designing materials with desired properties with metallocene catalyst mixtures, we investigated the characteristics of polypropylenes produced by mixtures of SiMe₂Ind₂ZrCl₂: dimethylsilane‐bis(indenyl) zirconocene ( 1 ) and Et(Flu)(Cp)ZrCl₂: ethylidene (fluorenyl cyclopentadienyl) zirconocene ( 2 ) in different proportions. The polymers were fractionated with solvents, and the fractions were characterized. We observed that the polymers produced by the different mixed systems showed lower weight‐average molecular weights and only slightly broader molecular weight distributions than polypropylenes synthesized by the individual catalysts. We concluded that catalyst 1 acted independently of catalyst 2 , producing polymers with the same isotacticity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1478–1485, 2003     

Copolymerization of 3‐buten‐1‐ol and propylene with an isospecific zirconocene/methylaluminoxane catalyst

The copolymerization of propylene and 3‐buten‐1‐ol protected with alkylaluminum [trimethylaluminum (TMA) or triisobutylaluminum] was conducted with an isospecific zirconocene catalyst [rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride], combined with methylaluminoxane as a cocatalyst, in the presence of additional TMA or H₂ as the chain‐transfer reagent if necessary. The results indicated that end‐hydroxylated polypropylene was obtained in the presence of the chain‐transfer reagents because of the formation of dormant species after the insertion of the 3‐buten‐1‐ol‐based monomer followed by chain‐transfer reactions. The selectivity of the chain‐transfer reactions was influenced by the alkylaluminum protecting the comonomer and the catalyst structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5600–5607, 2004     

Alumina as support for metallocene catalyst in ethylene polymerization

Aluminas thermally and/or chemically treated were used as support for Cp₂ZrCl₂ and evaluated in ethylene polymerization at constant reaction conditions. Two different calcination temperatures were employed, and the metallocene was fixed either directly or after support pretreatment with MAO, TMA, or NaOH solutions. The obtained alumina‐supported catalysts showed activities comparable to the homogeneous precursor. It was noticed that the textural properties of the supports strongly influenced the catalyst performance. The direct fixation of the metallocene on alumina produced catalysts presenting lower activities in comparison to the ones obtained from the chemically treated supports. The chemical pretreatment of hydrated alumina with TMA originated catalysts whose activities were superior to those obtained by pretreatment with MAO. The pretreatment with NaOH produced the more active catalyst and generated branched polymer. The molecular weight of the PE produced by the supported catalysts was higher than the ones obtained with the homogeneous system. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 9–21, 2004     

Synthesis and microstructural study of stereoblock elastomeric polypropylenes from metallocene catalyst (2‐PhInd)2ZrCl2 activated with cocatalyst mixtures

Various elastomeric polypropylenes (PPs) are synthesized through homogeneous propylene polymerization with metallocene catalyst (2‐PhInd)₂ZrCl₂ in the presence of different cocatalyst mixtures: triethylaluminum (TEA)/methylaluminoxane (MAO) or triisobutylaluminum (TIBA)/MAO in the range of Al_AlR3/Al_MAO = 0.0–0.9. The cocatalyst formulation impacts the resultant polymer microstructure and the thermal and dynamic mechanical properties of the produced PPs. ¹³C NMR analysis of the polymers reveals essentially atactic PP, with mmmm = 7.9%, when Al_AlR3/Al_MAO = 0.0. The mmmm pentad content is maximized when Al_AlR3/Al_MAO = 0.8; for TIBA, mmmm = 23.5%; and for TEA, mmmm = 17.6%. Differential scanning calorimetry analysis and dynamic mechanical thermal analysis corroborate these findings. Specifically, T_m, ΔH_m, and T_g are essentially maximized under these conditions, and the minimum damping is observed for Al_AlR3/Al_MAO = 0.6–0.8. ¹H NMR analysis of the mixtures of catalyst and cocatalysts (without monomer) shows very minor differences for [Zr]:Al_AlR3 in the range of 1:1–1:5. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Titanium complexes bearing carbamato ligands as catalytic precursors for propylene polymerization reactions

This report describes propylene polymerization reactions with titanium complexes bearing carbamato ligands, Ti(O₂CNMe₂)Cl₂ ( I ) and Ti(O₂CR₂)₄ [R₂ = NMe₂ ( II ), NEt₂ ( III ) and ( IV )]. Combinations of these complexes and MAO form catalysts for the synthesis of atactic polypropylene, as confirmed by FT‐IR, DSC and ¹³C NMR analysis. Effects of main reaction parameters on the catalyst activity were studied including the type of complex, solvent, temperature, and the [Al]/[Ti] molar ratio. The highest activity was observed when chlorobenzene was used as a solvent and AlMe₃‐depleted MAO was employed as a cocatalyst. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4095–4102     

The relationship between catalyst precursors and chain end groups in homogeneous propene polymerization catalysis

The chain transfer to monomer reactions promoted by primary and secondary growing chains in the propene polymerization promoted by ansa‐zirconocenes and postmetallocene precursors are studied by using DFT methods. From the theoretical results it comes out that the prevalence of propene insertion over β‐hydrogen transfer to the monomer decreases drastically in the presence of a secondary chain. Furthermore, we explained the reason why C₂‐symmetric metallocene catalysts promote the selective formation of cis but‐2‐enyls end group after a 2,1 inserted unit whereas for octahedral bis(phenoxy‐imine)titanium‐based catalysts, chain release promotes exclusively the formation of allyl terminated chain end. These results might be useful to design ligand precursors able to obtain not only high M_n PP polymers but also tuned chain end groups to build new polymer architectures. Overall, a more general picture of the enantioselectivity of the chain transfer to monomer processes is reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 699–708, 2010     

Copolymerization of propylene and disubstituted diallylsilanes involving intramolecular cyclization with stereoselective zirconocene catalysts

The copolymerization of propylene and disubstituted diallylsilanes [(CH₂ ?CH? CH₂? )₂R₂Si (R = CH₃ or C₆H₅)] was investigated with isoselective and syndioselective zirconocene catalysts with methylaluminoxane as a cocatalyst. The syndioselective catalyst showed a higher reactivity for disubstituted diallylsilanes than the isoselective catalysts. Diallyldimethylsilane was incorporated into the polymer chain via cyclization insertion preferentially and formed 3,5‐disubstituted dimethylsilacyclohexane units in the polypropylene main chain. In the copolymerization with diallyldiphenylsilane, diallyldiphenylsilane was copolymerized via both cyclization insertion and 1,2‐insertion, which formed a pendant allyl group. The structures of isolated silacyclohexane units, determined by ¹³C NMR and distortionless enhancement by polarization transfer spectroscopy, proved that the 1,2‐insertion of diallylsilanes proceeded with enantiomorphic site control; however, the diastereoselectivity of the cyclization reaction was independent of the stereoselectivity of the catalysts used, and cis‐silacyclohexane units were mainly formed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6083–6093, 2006     

Propylene polymerizations with a binary metallocene system—Chain shuttling caused by trimethylaluminium between active catalyst centers

Propylene was polymerized at varying trimethylaluminium (TMA) concentration with a homogeneous binary metallocene catalyst system activated by methylaluminoxane (MAO) in an attempt to better understand interactions between active catalyst sites and to clarify the role of the TMA as a chain shuttling agent. TMA‐free polymerization conditions were obtained by chemical treatment of MAO solution with 2,6‐di‐tert‐butyl‐4‐methylphenol (BHT). A binary catalyst system consisting of catalyst precursors diphenylmethyl(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride ( 1 ) producing high M_w syndiotactic polypropylene and rac‐dimethylsilylbis(4‐tert‐butyl‐2‐methyl‐cyclopentadienyl)zirconium dichloride ( 2 ) producing low M_w isotactic polypropylene was investigated. At the studied polymerization conditions, chain shuttling between the active catalysts caused by TMA was confirmed. The chain shuttling reactions caused changes in catalyst activity, molecular weights, melting behavior, and polymer microstructure. We propose that TMA is capable to transfer a growing polymer chain from catalyst 2 to catalyst 1 , and a stereoblock copolymer is formed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1364–1376, 2007     

The degree of crystallinity of monoclinic isotactic poly(propylene)

The degree of crystallinity of a set of monoclinic (alpha) isotactic poly(propylenes), prepared by a metallocene‐type catalyst, were determined at room temperature. Three different methods were used: density, enthalpy of fusion, and wide‐angle X‐ray scattering, and the results compared. The relation between the heat of fusion and the specific volume of these poly(propylenes) was found to be nonlinear, thus precluding any linear extrapolation to obtain the heat of fusion of the pure crystal (ΔH_u). The value of ΔH_u obtained from depression of the melting temperature by diluents is used. Based on the unit cell density of monoclinic crystals formed from a low defected fraction, the density obtained crystallinity levels were found to be between 0.l5–0.25 higher than those calculated from the heat of fusion. This relatively large difference holds for the isothermally crystallized and quenched isotactic poly(propylenes), and reflects the contribution of the interphase to the density determined crystallinity, which does not contribute to the heat of fusion. Paralleling results found in other systems, the crystallinity levels obtained from wide‐angle X‐ray scattering agree with those obtained from density, indicating a significant contribution of the partially ordered phase to the total diffraction. Emphasis is given on the need to account for the large differences in the crystallinities of poly(propylene) measured by different techniques when evaluating the dependence of properties on this quantity. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 323–334, 1999     

Efficient and tailored polymerization of olefins and styrene by metallocene catalysts

Different optimised new c_s-symmetric ansa zirconocenes were used for the homopolymerization of propene - activated by methylaluminoxane (MAO) with an Al : Zr molar ratio of 2000. In a series of experiments, the polymerisation temperature was varied in a range from 0 to 60°C. The obtained syndiotactic polypropenes show highly isotacticities up to rrrr pentads of 98% and melting points of 150°C. Stereoselectivities are sensitive to the monomer concentration, showing decreasing syndiotacticities with decreasing propene concentration due to increasing amount of skipped insertion which is demonstrated for the zirconium catalyst.     

13C NMR determination of the microstructure of polypropylene obtained with the DADNi(NCS)2/methylaluminoxane catalyst system

A complete ¹³C NMR characterization of a polymer synthesized with a new Ni‐diimine complex [DADNi(NCS)₂, where DAD = 2,6‐iPr? C₆H₃? N?C(Me)? C(Me)? N? 2,6‐iPr? C₆H₃] activated by methylaluminoxane by homopolymerization of propylene is presented. The amorphous material was made up mainly of blocks of syndiotactic polypropylene and ethylene–propylene copolymer. Some degree of propylene inversion (<1.2 mol %) and of long isobutyl and 2‐methyl hexyl branching (<1 mol %) were assigned and quantified. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2171–2178, 2004     

Copolymerization of Propene and 5‐Vinyl‐2‐Norbornene: A Simple Route to Polar Poly(propylene)s

Summary: The metallocenes rac‐C₂H₄(Ind)₂ZrCl₂ ( 1 ), rac‐Me₂Si(Ind)₂ZrCl₂ ( 2 ), and rac‐Me₂Si(2‐Me‐benz[e]Ind)₂ZrCl₂ ( 3 ) efficiently copolymerize propene and 5‐vinyl‐2‐norbornene (VNB). 1 and 2 give a high VNB content and high productivities, whereas 3 gives moderate incorporation. Surprisingly, precatalysts 1 and 2 , which have very closely related structures, showed very different reactivities toward VNB, with 1 having a greater affinity for VNB than for propene. The copolymers are quantitatively converted into polyolefins with polar functionalities.

     

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

Poly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C₂‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units ( 1,4‐BD ) and 1,2‐inserted units ( 1,2‐BD ) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (M_n) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI₆/SnMe₄/propyl acetate catalyst system. The ¹H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007     

The discovery of isotactic polypropylene and its impact on pure and applied science

This article recalls some aspects of the fascinating history of the discovery by Giulio Natta and his research group of the stereoselective polymerization of propylene and the understanding of the relationships between structure and properties of semicrystalline polymers. The impact of the discovery of isotactic polypropylene and stereoregular polymers on pure and applied science is briefly outlined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 391–395, 2004     

A Novel Synthetic Procedure for Stereoblock Poly(propylene) with a Living Polymerization System

Summary: Propylene polymerization was conducted at 0 °C in heptane or chlorobenzene (CB) by an ansa‐fluorenylamidodimethyltitanium complex combined with dried, modified methylaluminoxane that had been treated by dilution with heptane and successively repeatedly vacuum dried to remove any free trialkylaluminiums. The post‐polymerizations testified that the living polymerization proceeded irrespective of the solvent used. The heptane system gave the syndiotactic poly(propylene)s (PPs), whereas the CB system gave almost atactic PPs. After the first polymerization in heptane had been completed, the same amounts of propylene and CB were added for the second polymerization. This procedure gave the syndiotactic‐atactic stereoblock PP with narrow molecular‐weight distributions.

Structure of the ansa‐fluorenylamidodimethyltitanium complex and its application to the synthesis of syndiotactic‐atactic stereoblock poly(propylene)s reported here.     

Derivatization of propene/methyloctadiene copolymers: A flexible approach to side‐chain‐functionalized polypropenes

The copolymerization of propene with 7‐methyl‐1,6‐octadiene (MOD) catalyzed by Cp*TiMe₃/B(C₆F₅)₃ ( A ) and rac‐C₂H₄(Ind)₂ZrCl₂/methylaluminoxane ( B ) in toluene under 1 bar propene gave copolymers with unsaturated side chains. Under these conditions, catalyst A produced copolymers with an atactic backbone structure of type 1 , with 3.5–19.6 mol % MOD incorporation and weight‐average molecular weight = 0.7–2.7 × 10⁵. Using catalyst B , copolymers 2 with 0.4–3.8 mol % MOD incorporation were prepared. The comonomer incorporation was a linear function of the feed ratio. The titanium catalyst A had a significantly higher affinity for MOD than the sterically more hindered zirconocene B . Postpolymerization modification of the side‐chain C?C bond allowed the facile introduction of a wide variety of functional groups. Epoxidation and especially ozonolysis of the C?C bond, to give ? CHO and ? COOH functionalized copolymers, proved to be very facile routes to functionalized polypropenes. According to monitoring by NMR, most of these transformations proceed in an essentially quantitative conversion. As an example of potential applications of such polymers, polypropenes with covalently attached dyes were prepared that are suitable for blending. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1484–1497, 2002     

Stereospecific polymerization of methacrylates by metallocene and related catalysts

Stereospecific—isospecific, syndiospecific, and diastereospecific—polymerizations of methacrylates using group 4 metallocene and related catalysts produce polymethacrylates with controlled stereo‐microstructures. The versatility and stereospecificity of these cat‐ alysts for methyl methacrylate polymerization were demonstrated not only in solution‐phase polymerization, but also in polymerizations on silica surfaces and inside silicate nanogalleries. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3395–3403, 2004     

New architecture of supported metallocene catalysts for alkene polymerization

We report the synthesis of a supported metallocene catalyst that exhibits the same activity as a homogeneous catalyst for ethylene polymerization reactions. The key to this new catalytic system is a hybrid organic–inorganic polymer obtained by the cocondensation of an organotrialkoxysilane (OTAS; 40 mol %) with tetraethoxysilane (TEOS; 60 mol %). The particular organic group of OTAS enabled us to avoid gelation when the hydrolytic condensation was performed with a thermal cycle attaining 150 °C. The resulting product [soluble functionalized silica (SFS)] was a glass at room temperature that was soluble in several organic solvents such as tetrahydrofuran and toluene. The ²⁹Si NMR spectrum of SFS showed that the OTAS units were fully condensed (T₃ species), whereas the TEOS units were mainly present as tricondensed (Q₃) and tetracondensed (Q₄) units. SFS was grafted onto activated silica through a reaction of silanol groups. The metallocene [(nBuCp)₂ZrCl₂] was covalently bonded to the SFS‐modified support. The polymerization of ethylene was carried out in toluene in the presence of methylaluminoxane. The activity of the supported catalyst was similar to that of the metallocene catalyst in solution. The simplest explanation accounting for this fact is that most of the metallocene was grafted to SFS species issuing from the surface of the support through a reaction with their silanol groups. This improved the accessibility of the monomer to the reaction sites. Specific interactions of the metallocene species with neighboring organic branches of SFS might also affect the catalytic activity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5480–5486, 2007