Chain Transfer to Solvent in Propene Polymerization with Ti Cp-phosphinimide Catalysts: Evidence for Chain Termination via Ti–C Bond Homolysis

Ehm, Christian; Cipullo, Roberta; Passaro, M; Zaccaria, Francesco; Budzelaar, Peter H. M.; Busico, Vincenzo

doi:10.1021/acscatal.6b02738

Cited by 31 publications

(48 citation statements)

References 32 publications

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“…However, we noted that capture can lead to different β‐agostic olefin complexes, depending on the catalyst, and their role will be explained in the following. The chosen protocol has been benchmarked for polymerization related problems and has been shown to reproduce different experimental problems as for example absolute propagation barriers, (g) the copolymerization factor r e , chain transfer to solvent, and metal carbon bond strengths under polymerization conditions …”

Section: Resultsmentioning

confidence: 99%

Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity

Zaccaria

Cipullo

Budzelaar

et al. 2017

J. Polym. Sci. Part A: Polym. Chem.

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Available exptl. data for several metallocenes indicate that the ethene/propene copolymn. ratio rc can be much more temp. dependent than would be expected if competing insertion transition states (TS) are rate limiting. Detailed exploration of the reaction paths reveals in several cases the existence of a "capture-like" transition state before the actual insertion, with free energies close to the insertion TS. Movement around these transition states does not just involve monomer and chain, but also clear distortion of the ligand skeleton to allow entry of the monomer. Taking these addnl. TSs into account leads to much improved agreement with expt. for a series of metallocenes and a constrained geometry catalyst system. Depending on catalyst and temp., selectivity is detd. by competing insertion/insertion, capture/insertion or capture/capture. It seems likely that this is a common situation esp. for highly efficient catalysts, complicating (but not preventing) prediction of copolymn. performance

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Section: Resultsmentioning

confidence: 99%

Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity

Zaccaria

Cipullo

Budzelaar

et al. 2017

J. Polym. Sci. Part A: Polym. Chem.

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“…Transition states were located by direct optimization from a suitable initial geometry. Both energies and structures were calculated at the M06‐2X level of theory . Solvent effects including contributions of non‐electrostatic terms have been estimated in single point calculations on the gas‐phase optimized structures, based on the polarizable continuous solvation model PCM, default keyword SCRF=(Solvent=Toluene) in Gaussian 09.…”

Section: Methodsmentioning

confidence: 99%

Internal Donors in Ziegler–Natta Systems: is Reduction by AlR₃ a Requirement for Donor Clean‐Up?

et al. 2018

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Alkyl benzoates, phthalates, and succinates are used as “internal donors” (ID) to modify the surface of MgCl2‐supported Ziegler–Natta (ZN) catalysts for polypropylene production. Phthalates, in particular, are the working horses of this catalysis, but a REACH ban of these compounds for other applications has generated a desire from the market for phthalate‐free ZN catalysts, which has in turn triggered a search for alternatives and revamped research in the area. It has been reported that under polymerization conditions certain ID classes undergo an extensive exchange with alkoxysilane “external donors” (ED), which represents an important opportunity for surface fine‐tuning. ID clean‐up has been attributed to ester group reduction by the AlR3 cocatalyst. We have now measured the activation parameters for the reactions of ethyl benzoate (EB), dibutyl phthalate (DBP), and diethyl 2,3‐diisobutylsuccinate (DiBS) with AlEt3 in toluene solution by means of variable‐temperature 1H NMR spectroscopy. Reduction is fast for EB and DBP, whereas it is slow for DiBS. Results of DFT calculations are in line with the observed reactivity. Therefore, we conclude that an irreversible reaction with AlEt3 is not the only option for ID/ED exchange. Possible alternatives are discussed.

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“…[12] To date, the only chain transfer to toluene was reported by Busico group in 2016 for propylene polymerization using Cp-phosphinimide Ti catalysts. [13] The chain transfer follows radical mechanism: homolysis of TiÀC bond arouses polypropenyl radical to abstract benzylic proton; the obtained benzyl radical combines with Ti cationic species to initiate propylene coordination polymerization. Thus, chain transfer to solvent in coordination polymerization is still an open research area.…”

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confidence: 99%

Chain Transfer to Toluene in Styrene Coordination Polymerization

et al. 2020

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The chain‐transfer reaction is rather important in coordination polymerization regarding catalytic efficiency, adjustment of molecular weight, and control of chain structure. To date, chain transfer to H2 and Al, Mg, and Zn alkyl compounds and β‐H elimination are the commonly encountered modes. Now a novel chain transfer to toluene is reported. By introducing fluorine atoms into the β‐diketimine ligands, an inert catalytic system for styrene (St) coordination polymerization was transferred into the highly active one. The activity increased with an increase in the number of fluorines in the ligands. Surprisingly, the molecular weights of resultant polystyrenes are very low (Mn=2000–6600 Da) despite of St loadings, corresponding up to 121 chains per active species. The mechanisms were investigated by DFT simulation, MALDI‐TOF MS, isotope tracing experiment and 2D NMR spectrum analyses, which revealed that the fluorine activated the polymerization and directed chain transfer to toluene.

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Chain Transfer to Solvent in Propene Polymerization with Ti Cp-phosphinimide Catalysts: Evidence for Chain Termination via Ti–C Bond Homolysis

Cited by 31 publications

References 32 publications

Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity

Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity

Internal Donors in Ziegler–Natta Systems: is Reduction by AlR₃ a Requirement for Donor Clean‐Up?

Chain Transfer to Toluene in Styrene Coordination Polymerization

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Chain Transfer to Solvent in Propene Polymerization with Ti Cp-phosphinimide Catalysts: Evidence for Chain Termination via Ti–C Bond Homolysis

Cited by 31 publications

References 32 publications

Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity

Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity

Internal Donors in Ziegler–Natta Systems: is Reduction by AlR3 a Requirement for Donor Clean‐Up?

Chain Transfer to Toluene in Styrene Coordination Polymerization

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Internal Donors in Ziegler–Natta Systems: is Reduction by AlR₃ a Requirement for Donor Clean‐Up?