The Experts below are selected from a list of 21042 Experts worldwide ranked by ideXlab platform
Gerhard Erker - One of the best experts on this subject based on the ideXlab platform.
-
Bio-Organometallic Chemistry, ansa-Metallocenes, and Frustrated Lewis Pairs: Functional Group Chemistry at the Group 4 Bent Metallocenes
Organometallics, 2011Co-Authors: Gerhard ErkerAbstract:Functional group chemistry at the group 4 bent Metallocenes is still a challenge, due to the special features of these early-metal systems. Nevertheless, an increasing number of reactions and protocols is being developed for attaching organic functional groups at the bent-Metallocene frameworks and for carrying out reactions with them. Here some bio-organometallic bent Metallocene systems are discussed. Chemical transformations are presented and discussed, including olefin metathesis and even variants of the Mannich reaction. It is shown that intramolecular [2 + 2] cycloaddition reactions between alkenyl substituents at the Cp or indenyl rings under dynamic topochemical reaction control can lead to ansa-Metallocenes. Frustrated Lewis pair chemistry provides tools, for example, for reduction reactions under very mild conditions.
-
ansa Metallocenes by intramolecular ring closure reactions syntheses and applications
Macromolecular Symposia, 2006Co-Authors: Gerhard ErkerAbstract:Examples of a functional group chemistry at the Group 4 bent Metallocene frameworks are presented and discussed that allow for the preparation of ansa-Metallocenes at the stage of the intact organometallic complexes. These examples include ansa-Metallocene formation by means of intramolecular olefin metathesis reactions, by photochemical [2+2] cycloadditions of pendant olefinic moieties and even of a Mannich-type carbon carbon coupling reaction of enamino substituents attached at the Cp-rings. Many of the resulting ansa-Metallocene systems were employed as components of reactive homogeneous Ziegler-Natta olefin polymerization and copolymerization catalysts. The Mannich coupling reaction was also used in [3] ferrocenophane chemistry, eventually leading to novel chelate ligand systems that were employed in catalytic asymmetric polyketone formation.
-
Ansa‐Metallocenes by Intramolecular Ring Closure Reactions – Syntheses and Applications
Macromolecular Symposia, 2006Co-Authors: Gerhard ErkerAbstract:Examples of a functional group chemistry at the Group 4 bent Metallocene frameworks are presented and discussed that allow for the preparation of ansa-Metallocenes at the stage of the intact organometallic complexes. These examples include ansa-Metallocene formation by means of intramolecular olefin metathesis reactions, by photochemical [2+2] cycloadditions of pendant olefinic moieties and even of a Mannich-type carbon carbon coupling reaction of enamino substituents attached at the Cp-rings. Many of the resulting ansa-Metallocene systems were employed as components of reactive homogeneous Ziegler-Natta olefin polymerization and copolymerization catalysts. The Mannich coupling reaction was also used in [3] ferrocenophane chemistry, eventually leading to novel chelate ligand systems that were employed in catalytic asymmetric polyketone formation.
-
group 4 bent Metallocenes and functional groups finding convenient pathways in a difficult terrain
Coordination Chemistry Reviews, 2006Co-Authors: Gerhard Erker, Gerald Kehr, Roland FröhlichAbstract:Abstract Current approaches toward the development of functional group chemistry with sensitive Group 4 bent Metallocenes are discussed. This includes polymerization reactions of functionalized olefins, electrophilic attack at the Metallocene Cp-rings, the introduction of functional groups via fulvene routes, the reactions of pendant functional groups, including CH-activation reactions, Mannich-type carbon–carbon coupling reactions, olefin metathesis reactions and photochemical [2 + 2] cycloadditions. The formation of chelate–PR 2 -bridged metal–metal bonded early–late heterobimetallic bent Metallocene derivatives is presented and some of their reactions are discussed.
-
(Butadiene)Metallocene/B(C6F5)3 Pathway to Catalyst Systems for Stereoselective Methyl Methacrylate Polymerization: Evidence for an Anion Dependent Metallocene Catalyzed Polymerization Process
Journal of the American Chemical Society, 2004Co-Authors: Joachim W Strauch, Roland Fröhlich, Gerald Kehr, Jeanluc Faure, Stephane Bredeau, Cun Wang, Heinrich Luftmann, Gerhard ErkerAbstract:The ansa-zirconocene dichlorides [Me2Si(C5H4)(3-R-C5H3)]ZrCl2 7a−e (R = H, CH3, cyclohexyl, −CHMe2, −CMe3) were reacted with butadiene−magnesium to yield the respective (η4-butadiene)Metallocenes 17a−e. The chiral examples give a mixture of two s-cis and two s-trans diastereomers. The strong Lewis acid B(C6F5)3 adds selectively to a terminal butadiene carbon atom to yield the (butadiene)Metallocene/B(C6F5)3 betaine complexes 18a−e. Initially, the formation of the Z-18 isomers is preferred. These consecutively rearrange to the thermodynamically favored isomers E-18. The dipolar systems 18 are active single component Metallocene catalysts for the stereospecific polymerization of methyl methacrylate. With increasing steric bulk of the attached single alkyl substituent an increasingly isotactic poly(methyl methacrylate) is obtained. A similar trend is observed in the methyl methacrylate polymerization at the [Me2Si(C5H4)(3-R-C5H3)]ZrCH3+ catalysts (9a−e) that were conventionally prepared by methyl abstraction...
Franco M Rabagliati - One of the best experts on this subject based on the ideXlab platform.
-
HOMO- AND COPOLYMERIZATION OF STYRENE AND STYRENE RELATED MONOMERS. SYNTHESIS AND CHARACTERIZATION
Journal of The Chilean Chemical Society, 2016Co-Authors: Franco M Rabagliati, Rodrigo A. Cancino, M. Verónica Cuevas, Héctor E. Muñoz, Gonzalo A Mardones, Marcela Saavedra, Francisco J. Rodriguez, Monica A Perez, M. Vidal, Lisa MuñozAbstract:Systems including diphenylzinc, Metallocene, and methylaluminoxane, at various combinations has been attempted, as initiating systems for homo- and copolymerization of styrene and various styrene related comonomers including : substituted styrenes, styrene derivatives, α-olefins, dienes and more recently cycohexenes including norbornene. The used Metallocenes were those containing titanium, zirconium and for comparatives reasons hafnium. The Metallocene efficiency towards syndiotactic polystyrene polymerization showed the order : titanocene > zirconocene > hafnocene. While the polymerization as well the copolymerization of Styrene with related to styrene compounds resulted to be much influenced by both electrical and steric hindrance effect. For styrene substituted derivative those group or element having I+ inductive effect depending its position at styrene’s its phenyl ring favours homopolymerization as well their copolymerization with styrene. The steric hindrance also showed a determinant influence on reactivity, so methyl and tert-butyl group, having a I+ effect, when at para -position improve activity and stereoregularity of their polymerization processes. But when placing at orto- position showed a very low capacity to polymerize. The present and previous results indicate that polymerization processes are initiated by monomer coordination to active metal species either of the binary Metallocene-MAO or of the ternary Ph2Zn-Metallocene-MAO.
-
styrene styrene derivative copolymerization by ph2zn Metallocene mao systems homo and copolymerization of a methylstyrene with styrene
Journal of The Chilean Chemical Society, 2010Co-Authors: Franco M Rabagliati, Héctor E. Muñoz, Gonzalo A MardonesAbstract:The copolymerization of styrene with α-methylstyrene has been tested using combined Metallocene-MAO initiator systems with and without diphenylzinc. The Metallocenes used were biscyclopentadienyltitanium dichloride, Cp 2 TiCl 2 , bis(n-butylcyclopentadienyl)titanium dichloride, (n-BuCp) 2 TiCl 2 , and the halfsandwich Metallocene indenyltitanium trichloride, IndTiCl 3 . The results indicate that both binary Metallocene-MAO, and ternary Ph 2 Zn-Metallocene-MAO systems are capable of polymerizing α-methylstyrene to poly(α-methylstyrene) as well of its copolymerization with styrene. These initiator systems also show that despite the I+ inductive effect of the methyl group, which enhances electron density at the vinyl double bond of styrene, the steric consequence of vinyl substitution hinders monomer coordination to active species, causing a decrease in conversion of either α-MeS to homopolymer or S/α-MeS to the corresponding copolymer. The nature and structure of the Metallocene included in the initiator system are determinant of the initiator system’s efficiency. For the Metallocenes used the efficiency follows the order IndTiCl 3 > Cp 2 TiCl 2 > (n-BuCp) 2 TiCl 2 , with the half-sandwich Metallocene IndTiCl 3 showing greater efficiency than the true Metallocenes.
-
further studies on styrene styrene derivative copolymerizations using combined diphenylzinc additive initiator systems
Polymer International, 2005Co-Authors: Franco M Rabagliati, Carlos J Caro, Francisco J. Rodriguez, Monica A Perez, Nicolas CrispelAbstract:A combination of diphenylzinc, a Metallocene and methylaluminoxane (Ph2Zn-Metallocene-MAO) is a suitable initiator system for the polymerization of styrene and for its copolymerization with para-alkyl substituted styrenes. This paper reports new experimental results which reinforce our previous findings indicating that polymerization processes are initiated by monomer coordination to active species resulting from these particular combined systems. Polymerization propagates by a cationic pathway. Further to our previous observation that the I+ inductive effect of para-substituents in styrene improves conversion to polymer, we now find that methyl substitution on the vinyl double bond of styrene, in spite of the I+ inductive effect and as a result of increased steric hindrance, makes the polymerization process difficult. On the other hand, the replacement of titanocenes by zirconocenes or hafnocenes generates Ph2Zn-Metallocene-MAO initiator systems which are also able to induce homo- and copolymerization, but with lower yields and producing practically amorphous polymers. The efficiency of our Ph2Zn-Metallocene-MAO initiator systems follows the order titanocene > zirconocene > hafnocene, at least for the studied Metallocenes. Copyright © 2004 Society of Chemical Industry
-
Further studies on styrene/styrene derivative copolymerizations using combined diphenylzinc-additive initiator systems †
Polymer International, 2004Co-Authors: Franco M Rabagliati, Carlos J Caro, Francisco J. Rodriguez, Monica A Perez, Nicolas CrispelAbstract:A combination of diphenylzinc, a Metallocene and methylaluminoxane (Ph2Zn-Metallocene-MAO) is a suitable initiator system for the polymerization of styrene and for its copolymerization with para-alkyl substituted styrenes. This paper reports new experimental results which reinforce our previous findings indicating that polymerization processes are initiated by monomer coordination to active species resulting from these particular combined systems. Polymerization propagates by a cationic pathway. Further to our previous observation that the I+ inductive effect of para-substituents in styrene improves conversion to polymer, we now find that methyl substitution on the vinyl double bond of styrene, in spite of the I+ inductive effect and as a result of increased steric hindrance, makes the polymerization process difficult. On the other hand, the replacement of titanocenes by zirconocenes or hafnocenes generates Ph2Zn-Metallocene-MAO initiator systems which are also able to induce homo- and copolymerization, but with lower yields and producing practically amorphous polymers. The efficiency of our Ph2Zn-Metallocene-MAO initiator systems follows the order titanocene > zirconocene > hafnocene, at least for the studied Metallocenes. Copyright © 2004 Society of Chemical Industry
-
copolymerization of styrene by diphenylzinc additive systems i copolymerization of styrene p tert butylstyrene by ph2zn Metallocene mao systems
European Polymer Journal, 2001Co-Authors: Franco M Rabagliati, Antxon Martínez De Ilarduya, Monica A Perez, Marcelo A Soto, Sebastian MunozguerraAbstract:Abstract Copolymerization of styrene (S) and p - tert -butylstyrene ( p -Bu t S) was carried out at 60°C using diphenylzinc–Metallocene–MAO systems. Metallocenes bisindenylzirconium dichloride, bis( n -butylcyclopentadienyl) titanium dichloride and cyclopentadienyltitanium trichloride were tried, the latter giving the largest conversion. Copolymers obtained with this system were analyzed by NMR and showed to be syndiotactic in nature and slightly richer in p -Bu t S than the initial feed from which they were formed.
Monica A Perez - One of the best experts on this subject based on the ideXlab platform.
-
HOMO- AND COPOLYMERIZATION OF STYRENE AND STYRENE RELATED MONOMERS. SYNTHESIS AND CHARACTERIZATION
Journal of The Chilean Chemical Society, 2016Co-Authors: Franco M Rabagliati, Rodrigo A. Cancino, M. Verónica Cuevas, Héctor E. Muñoz, Gonzalo A Mardones, Marcela Saavedra, Francisco J. Rodriguez, Monica A Perez, M. Vidal, Lisa MuñozAbstract:Systems including diphenylzinc, Metallocene, and methylaluminoxane, at various combinations has been attempted, as initiating systems for homo- and copolymerization of styrene and various styrene related comonomers including : substituted styrenes, styrene derivatives, α-olefins, dienes and more recently cycohexenes including norbornene. The used Metallocenes were those containing titanium, zirconium and for comparatives reasons hafnium. The Metallocene efficiency towards syndiotactic polystyrene polymerization showed the order : titanocene > zirconocene > hafnocene. While the polymerization as well the copolymerization of Styrene with related to styrene compounds resulted to be much influenced by both electrical and steric hindrance effect. For styrene substituted derivative those group or element having I+ inductive effect depending its position at styrene’s its phenyl ring favours homopolymerization as well their copolymerization with styrene. The steric hindrance also showed a determinant influence on reactivity, so methyl and tert-butyl group, having a I+ effect, when at para -position improve activity and stereoregularity of their polymerization processes. But when placing at orto- position showed a very low capacity to polymerize. The present and previous results indicate that polymerization processes are initiated by monomer coordination to active metal species either of the binary Metallocene-MAO or of the ternary Ph2Zn-Metallocene-MAO.
-
further studies on styrene styrene derivative copolymerizations using combined diphenylzinc additive initiator systems
Polymer International, 2005Co-Authors: Franco M Rabagliati, Carlos J Caro, Francisco J. Rodriguez, Monica A Perez, Nicolas CrispelAbstract:A combination of diphenylzinc, a Metallocene and methylaluminoxane (Ph2Zn-Metallocene-MAO) is a suitable initiator system for the polymerization of styrene and for its copolymerization with para-alkyl substituted styrenes. This paper reports new experimental results which reinforce our previous findings indicating that polymerization processes are initiated by monomer coordination to active species resulting from these particular combined systems. Polymerization propagates by a cationic pathway. Further to our previous observation that the I+ inductive effect of para-substituents in styrene improves conversion to polymer, we now find that methyl substitution on the vinyl double bond of styrene, in spite of the I+ inductive effect and as a result of increased steric hindrance, makes the polymerization process difficult. On the other hand, the replacement of titanocenes by zirconocenes or hafnocenes generates Ph2Zn-Metallocene-MAO initiator systems which are also able to induce homo- and copolymerization, but with lower yields and producing practically amorphous polymers. The efficiency of our Ph2Zn-Metallocene-MAO initiator systems follows the order titanocene > zirconocene > hafnocene, at least for the studied Metallocenes. Copyright © 2004 Society of Chemical Industry
-
Further studies on styrene/styrene derivative copolymerizations using combined diphenylzinc-additive initiator systems †
Polymer International, 2004Co-Authors: Franco M Rabagliati, Carlos J Caro, Francisco J. Rodriguez, Monica A Perez, Nicolas CrispelAbstract:A combination of diphenylzinc, a Metallocene and methylaluminoxane (Ph2Zn-Metallocene-MAO) is a suitable initiator system for the polymerization of styrene and for its copolymerization with para-alkyl substituted styrenes. This paper reports new experimental results which reinforce our previous findings indicating that polymerization processes are initiated by monomer coordination to active species resulting from these particular combined systems. Polymerization propagates by a cationic pathway. Further to our previous observation that the I+ inductive effect of para-substituents in styrene improves conversion to polymer, we now find that methyl substitution on the vinyl double bond of styrene, in spite of the I+ inductive effect and as a result of increased steric hindrance, makes the polymerization process difficult. On the other hand, the replacement of titanocenes by zirconocenes or hafnocenes generates Ph2Zn-Metallocene-MAO initiator systems which are also able to induce homo- and copolymerization, but with lower yields and producing practically amorphous polymers. The efficiency of our Ph2Zn-Metallocene-MAO initiator systems follows the order titanocene > zirconocene > hafnocene, at least for the studied Metallocenes. Copyright © 2004 Society of Chemical Industry
-
Ph_2Zn-Metallocene-MAO initiator systems in the homo- and copolymerization of styrene/p-alkylstyrene
Polymer Bulletin, 2003Co-Authors: Monica A Perez, Rodrigo A. Cancino, Carlos J Caro, F M RabagliatiAbstract:The homo- and copolymerization of styrene (S) with p-methylstyrene (p-MeS) and p-tert-butylstyrene (p-Bu^tS) has been tested using initiator systems of the Ph_2Zn-Metallocene-MAO type. The Metallocenes used were CpTiCl_3, IndTiCI_3, (n-BuCp)_2TiCl_2, Ind_2ZrCl_2 and Et(Ind)_2ZrCl_2. The Ph_2Zn-Metallocene-MAO systems homopolymerize styrene, p-methylstyrene and p-tert-butylstyrene, producing syndiotactic polymers in the case of the titanocenes and amorphous polymers in the case of the zirconocenes. The S/p-MeS and S/p-Bu^tS copolymers obtained with the Ph_2Zn-titanocene-MAO systems are enriched in the comonomer with respect to the initial feed.
-
copolymerization of styrene by diphenylzinc additive systems i copolymerization of styrene p tert butylstyrene by ph2zn Metallocene mao systems
European Polymer Journal, 2001Co-Authors: Franco M Rabagliati, Antxon Martínez De Ilarduya, Monica A Perez, Marcelo A Soto, Sebastian MunozguerraAbstract:Abstract Copolymerization of styrene (S) and p - tert -butylstyrene ( p -Bu t S) was carried out at 60°C using diphenylzinc–Metallocene–MAO systems. Metallocenes bisindenylzirconium dichloride, bis( n -butylcyclopentadienyl) titanium dichloride and cyclopentadienyltitanium trichloride were tried, the latter giving the largest conversion. Copolymers obtained with this system were analyzed by NMR and showed to be syndiotactic in nature and slightly richer in p -Bu t S than the initial feed from which they were formed.
Roland Fröhlich - One of the best experts on this subject based on the ideXlab platform.
-
group 4 bent Metallocenes and functional groups finding convenient pathways in a difficult terrain
Coordination Chemistry Reviews, 2006Co-Authors: Gerhard Erker, Gerald Kehr, Roland FröhlichAbstract:Abstract Current approaches toward the development of functional group chemistry with sensitive Group 4 bent Metallocenes are discussed. This includes polymerization reactions of functionalized olefins, electrophilic attack at the Metallocene Cp-rings, the introduction of functional groups via fulvene routes, the reactions of pendant functional groups, including CH-activation reactions, Mannich-type carbon–carbon coupling reactions, olefin metathesis reactions and photochemical [2 + 2] cycloadditions. The formation of chelate–PR 2 -bridged metal–metal bonded early–late heterobimetallic bent Metallocene derivatives is presented and some of their reactions are discussed.
-
(Butadiene)Metallocene/B(C6F5)3 Pathway to Catalyst Systems for Stereoselective Methyl Methacrylate Polymerization: Evidence for an Anion Dependent Metallocene Catalyzed Polymerization Process
Journal of the American Chemical Society, 2004Co-Authors: Joachim W Strauch, Roland Fröhlich, Gerald Kehr, Jeanluc Faure, Stephane Bredeau, Cun Wang, Heinrich Luftmann, Gerhard ErkerAbstract:The ansa-zirconocene dichlorides [Me2Si(C5H4)(3-R-C5H3)]ZrCl2 7a−e (R = H, CH3, cyclohexyl, −CHMe2, −CMe3) were reacted with butadiene−magnesium to yield the respective (η4-butadiene)Metallocenes 17a−e. The chiral examples give a mixture of two s-cis and two s-trans diastereomers. The strong Lewis acid B(C6F5)3 adds selectively to a terminal butadiene carbon atom to yield the (butadiene)Metallocene/B(C6F5)3 betaine complexes 18a−e. Initially, the formation of the Z-18 isomers is preferred. These consecutively rearrange to the thermodynamically favored isomers E-18. The dipolar systems 18 are active single component Metallocene catalysts for the stereospecific polymerization of methyl methacrylate. With increasing steric bulk of the attached single alkyl substituent an increasingly isotactic poly(methyl methacrylate) is obtained. A similar trend is observed in the methyl methacrylate polymerization at the [Me2Si(C5H4)(3-R-C5H3)]ZrCH3+ catalysts (9a−e) that were conventionally prepared by methyl abstraction...
-
butadiene Metallocene b c6f5 3 pathway to catalyst systems for stereoselective methyl methacrylate polymerization evidence for an anion dependent Metallocene catalyzed polymerization process
Journal of the American Chemical Society, 2004Co-Authors: Joachim W Strauch, Roland Fröhlich, Gerald Kehr, Jeanluc Faure, Stephane Bredeau, Cun Wang, Heinrich Luftmann, Gerhard ErkerAbstract:The ansa-zirconocene dichlorides [Me2Si(C5H4)(3-R-C5H3)]ZrCl2 7a−e (R = H, CH3, cyclohexyl, −CHMe2, −CMe3) were reacted with butadiene−magnesium to yield the respective (η4-butadiene)Metallocenes 17a−e. The chiral examples give a mixture of two s-cis and two s-trans diastereomers. The strong Lewis acid B(C6F5)3 adds selectively to a terminal butadiene carbon atom to yield the (butadiene)Metallocene/B(C6F5)3 betaine complexes 18a−e. Initially, the formation of the Z-18 isomers is preferred. These consecutively rearrange to the thermodynamically favored isomers E-18. The dipolar systems 18 are active single component Metallocene catalysts for the stereospecific polymerization of methyl methacrylate. With increasing steric bulk of the attached single alkyl substituent an increasingly isotactic poly(methyl methacrylate) is obtained. A similar trend is observed in the methyl methacrylate polymerization at the [Me2Si(C5H4)(3-R-C5H3)]ZrCH3+ catalysts (9a−e) that were conventionally prepared by methyl abstraction...
-
Organic Transformations at a Group 4 Metallocene Framework: Formation of a Rigid ansa-Metallocene by Mannich-type Carbon–Carbon Coupling
Angewandte Chemie International Edition, 1999Co-Authors: Stephanie Knüppel, Gerhard Erker, Roland FröhlichAbstract:New Metallocene Ziegler catalysts are generated by activation of the rigid ansa-Metallocenes 2 with methylalumoxane. Complexes 2 are formed by application of an acid-catalyzed Mannich reaction—a classical reaction from the synthetic organic repertoire—of complexes 1, which are readily available by means of a fulvene route.
Nicolas Crispel - One of the best experts on this subject based on the ideXlab platform.
-
further studies on styrene styrene derivative copolymerizations using combined diphenylzinc additive initiator systems
Polymer International, 2005Co-Authors: Franco M Rabagliati, Carlos J Caro, Francisco J. Rodriguez, Monica A Perez, Nicolas CrispelAbstract:A combination of diphenylzinc, a Metallocene and methylaluminoxane (Ph2Zn-Metallocene-MAO) is a suitable initiator system for the polymerization of styrene and for its copolymerization with para-alkyl substituted styrenes. This paper reports new experimental results which reinforce our previous findings indicating that polymerization processes are initiated by monomer coordination to active species resulting from these particular combined systems. Polymerization propagates by a cationic pathway. Further to our previous observation that the I+ inductive effect of para-substituents in styrene improves conversion to polymer, we now find that methyl substitution on the vinyl double bond of styrene, in spite of the I+ inductive effect and as a result of increased steric hindrance, makes the polymerization process difficult. On the other hand, the replacement of titanocenes by zirconocenes or hafnocenes generates Ph2Zn-Metallocene-MAO initiator systems which are also able to induce homo- and copolymerization, but with lower yields and producing practically amorphous polymers. The efficiency of our Ph2Zn-Metallocene-MAO initiator systems follows the order titanocene > zirconocene > hafnocene, at least for the studied Metallocenes. Copyright © 2004 Society of Chemical Industry
-
Further studies on styrene/styrene derivative copolymerizations using combined diphenylzinc-additive initiator systems †
Polymer International, 2004Co-Authors: Franco M Rabagliati, Carlos J Caro, Francisco J. Rodriguez, Monica A Perez, Nicolas CrispelAbstract:A combination of diphenylzinc, a Metallocene and methylaluminoxane (Ph2Zn-Metallocene-MAO) is a suitable initiator system for the polymerization of styrene and for its copolymerization with para-alkyl substituted styrenes. This paper reports new experimental results which reinforce our previous findings indicating that polymerization processes are initiated by monomer coordination to active species resulting from these particular combined systems. Polymerization propagates by a cationic pathway. Further to our previous observation that the I+ inductive effect of para-substituents in styrene improves conversion to polymer, we now find that methyl substitution on the vinyl double bond of styrene, in spite of the I+ inductive effect and as a result of increased steric hindrance, makes the polymerization process difficult. On the other hand, the replacement of titanocenes by zirconocenes or hafnocenes generates Ph2Zn-Metallocene-MAO initiator systems which are also able to induce homo- and copolymerization, but with lower yields and producing practically amorphous polymers. The efficiency of our Ph2Zn-Metallocene-MAO initiator systems follows the order titanocene > zirconocene > hafnocene, at least for the studied Metallocenes. Copyright © 2004 Society of Chemical Industry
