Isobutene polymerization and isobutene-isoprene copolymerization catalyzed by cationic zirconocene hydride complexes

Shaun Garratt; Andrew G. Carr; Gerhard Langstein; Manfred Bochmann

doi:10.1021/ma034320p

Isobutene polymerization and isobutene-isoprene copolymerization catalyzed by cationic zirconocene hydride complexes

Shaun Garratt, Andrew G. Carr, Gerhard Langstein, Manfred Bochmann

Research output: Contribution to journal › Article › peer-review

49 Citations (Scopus)

Abstract

The cationic zirconocene trihydrides [Cp‘₄Zr₂H(µ-H)₂]⁺X^-, generated from [Cp‘₂ZrH₂]₂ with various trityl salts of weakly coordinating anions, are powerful initiators for the polymerization of isobutene (IB) and its copolymerization with isoprene (IP) (Cp‘ = C₅H₄SiMe₃). This study is concerned with the quantification of the effects of the counteranion and of trace moisture on IB/IP copolymers and the nature of the initiating species. Polymer molecular weights increase with decreasing anion nucleophilicity in the order X = [B(C₆F₅)₄] ˜ [H₂N{B(C₆F₅)₃}₂] > [CN{B(C₆F₅)₃}₂]. Using [Cp‘₄Zr₂H₃]⁺ [CN{B(C₆F₅)₃}₂]^-, high copolymer molecular weights are found (M_w ˜ 5 × 10⁵ g/mol at -35 °C). There is little reduction in either rate or molecular weight on addition of isoprene. Polymer molecular weights are substantially higher than with the Et₂AlCl/^tBuCl initiator system under identical conditions. Water was shown to be an important chain-transfer agent; substoichiometric quantities of water reduced activity, and copolymer molecular weights decreased linearly with increasing [H₂O]. Mechanistic studies suggest that [Cp‘₄Zr₂H(µ-H)₂]⁺ does not itself act as a cationic initiator but is transformed into one or more other binuclear (polynuclear?) species, accompanied by alkene insertion into the Zr-H bond and a monomer hydrogenation step. Tentative structures for these reactive intermediates are suggested.

Original language	English
Pages (from-to)	4276-4287
Number of pages	12
Journal	Macromolecules
Volume	36
Issue number	12
DOIs	https://doi.org/10.1021/ma034320p
Publication status	Published - 14 May 2003

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10.1021/ma034320p

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@article{e8e285162ad04c758f19222e0c858311,

title = "Isobutene polymerization and isobutene-isoprene copolymerization catalyzed by cationic zirconocene hydride complexes",

abstract = "The cationic zirconocene trihydrides [Cp{\textquoteleft}4Zr2H(µ-H)2]+X-, generated from [Cp{\textquoteleft}2ZrH2]2 with various trityl salts of weakly coordinating anions, are powerful initiators for the polymerization of isobutene (IB) and its copolymerization with isoprene (IP) (Cp{\textquoteleft} = C5H4SiMe3). This study is concerned with the quantification of the effects of the counteranion and of trace moisture on IB/IP copolymers and the nature of the initiating species. Polymer molecular weights increase with decreasing anion nucleophilicity in the order X = [B(C6F5)4] ˜ [H2N{B(C6F5)3}2] > [CN{B(C6F5)3}2]. Using [Cp{\textquoteleft}4Zr2H3]+ [CN{B(C6F5)3}2]-, high copolymer molecular weights are found (Mw ˜ 5 × 105 g/mol at -35 °C). There is little reduction in either rate or molecular weight on addition of isoprene. Polymer molecular weights are substantially higher than with the Et2AlCl/tBuCl initiator system under identical conditions. Water was shown to be an important chain-transfer agent; substoichiometric quantities of water reduced activity, and copolymer molecular weights decreased linearly with increasing [H2O]. Mechanistic studies suggest that [Cp{\textquoteleft}4Zr2H(µ-H)2]+ does not itself act as a cationic initiator but is transformed into one or more other binuclear (polynuclear?) species, accompanied by alkene insertion into the Zr-H bond and a monomer hydrogenation step. Tentative structures for these reactive intermediates are suggested.",

author = "Shaun Garratt and Carr, {Andrew G.} and Gerhard Langstein and Manfred Bochmann",

year = "2003",

month = may,

day = "14",

doi = "10.1021/ma034320p",

language = "English",

volume = "36",

pages = "4276--4287",

journal = "Macromolecules",

issn = "0024-9297",

publisher = "American Chemical Society",

number = "12",

}

TY - JOUR

T1 - Isobutene polymerization and isobutene-isoprene copolymerization catalyzed by cationic zirconocene hydride complexes

AU - Garratt, Shaun

AU - Carr, Andrew G.

AU - Langstein, Gerhard

AU - Bochmann, Manfred

PY - 2003/5/14

Y1 - 2003/5/14

N2 - The cationic zirconocene trihydrides [Cp‘4Zr2H(µ-H)2]+X-, generated from [Cp‘2ZrH2]2 with various trityl salts of weakly coordinating anions, are powerful initiators for the polymerization of isobutene (IB) and its copolymerization with isoprene (IP) (Cp‘ = C5H4SiMe3). This study is concerned with the quantification of the effects of the counteranion and of trace moisture on IB/IP copolymers and the nature of the initiating species. Polymer molecular weights increase with decreasing anion nucleophilicity in the order X = [B(C6F5)4] ˜ [H2N{B(C6F5)3}2] > [CN{B(C6F5)3}2]. Using [Cp‘4Zr2H3]+ [CN{B(C6F5)3}2]-, high copolymer molecular weights are found (Mw ˜ 5 × 105 g/mol at -35 °C). There is little reduction in either rate or molecular weight on addition of isoprene. Polymer molecular weights are substantially higher than with the Et2AlCl/tBuCl initiator system under identical conditions. Water was shown to be an important chain-transfer agent; substoichiometric quantities of water reduced activity, and copolymer molecular weights decreased linearly with increasing [H2O]. Mechanistic studies suggest that [Cp‘4Zr2H(µ-H)2]+ does not itself act as a cationic initiator but is transformed into one or more other binuclear (polynuclear?) species, accompanied by alkene insertion into the Zr-H bond and a monomer hydrogenation step. Tentative structures for these reactive intermediates are suggested.

AB - The cationic zirconocene trihydrides [Cp‘4Zr2H(µ-H)2]+X-, generated from [Cp‘2ZrH2]2 with various trityl salts of weakly coordinating anions, are powerful initiators for the polymerization of isobutene (IB) and its copolymerization with isoprene (IP) (Cp‘ = C5H4SiMe3). This study is concerned with the quantification of the effects of the counteranion and of trace moisture on IB/IP copolymers and the nature of the initiating species. Polymer molecular weights increase with decreasing anion nucleophilicity in the order X = [B(C6F5)4] ˜ [H2N{B(C6F5)3}2] > [CN{B(C6F5)3}2]. Using [Cp‘4Zr2H3]+ [CN{B(C6F5)3}2]-, high copolymer molecular weights are found (Mw ˜ 5 × 105 g/mol at -35 °C). There is little reduction in either rate or molecular weight on addition of isoprene. Polymer molecular weights are substantially higher than with the Et2AlCl/tBuCl initiator system under identical conditions. Water was shown to be an important chain-transfer agent; substoichiometric quantities of water reduced activity, and copolymer molecular weights decreased linearly with increasing [H2O]. Mechanistic studies suggest that [Cp‘4Zr2H(µ-H)2]+ does not itself act as a cationic initiator but is transformed into one or more other binuclear (polynuclear?) species, accompanied by alkene insertion into the Zr-H bond and a monomer hydrogenation step. Tentative structures for these reactive intermediates are suggested.

U2 - 10.1021/ma034320p

DO - 10.1021/ma034320p

M3 - Article

VL - 36

SP - 4276

EP - 4287

JO - Macromolecules

JF - Macromolecules

SN - 0024-9297

IS - 12

ER -