Dialkoxy-Substituted, C1-Symmetric Metallocenes: Synthesis and Catalytic Behavior in the Propylene Polymerization Reaction

The synthesis of a series of C1-symmetric metallocene complexes rac-[1-(5,6-dialkoxy-2-methyl- 1-η5-indenyl)-2-(9-η5-fluorenyl)ethane]zirconium dichlorides (alkyl: n-butyl, n-hexyl, n-octyl, n-decyl) is described. These complexes are versatile catalysts in the polymerization of propylene after in situ activation with triisobutylaluminum (TIBA) and Ph3C[B(C6F5)4] in toluene and heptane solution. All catalysts show higher solubility and improved polymerization properties in industrially used hydrocarbon solvents (e.g. heptane). However, the molecular weights and isotacticity values of the resulting polypropylene materials are decreased compared to the ethoxy-bridged analogue rac- [1-(5,6-ethylenedioxy-2-methyl-η5-indenyl)-2-(9-η5-fluorenyl)ethane]zirconium dichloride. A possible explanation is based on enhanced interaction of the active catalyst centers with Al(III) scavenger molecules even at low Al : Zr ratios, leading to reversible chain transfer.

Download Full-text

Reversible Chain Transfer Catalyzed Polymerization of Methyl Methacrylate with In-Situ Formed Alkyl Iodide Initiator

Australian Journal of Chemistry ◽

10.1071/ch09229 ◽

2009 ◽

Vol 62 (11) ◽

pp. 1492 ◽

Cited By ~ 9

Author(s):

Atsushi Goto ◽

Koji Nagasawa ◽

Ayaka Shinjo ◽

Yoshinobu Tsujii ◽

Takeshi Fukuda

Keyword(s):

Methyl Methacrylate ◽

Chain Transfer ◽

Alkyl Iodide ◽

Nitrogen And Phosphorus ◽

Molecular Weights ◽

Living Radical Polymerizations ◽

Low Mass ◽

Reversible Chain Transfer ◽

Catalyzed Polymerization

A method utilizing generation of an alkyl iodide (low-mass dormant species) in situ formed in polymerization was adopted to reversible chain transfer catalyzed polymerizations (RTCP) (living radical polymerizations) with several nitrogen and phosphorus catalysts. The polymerization of methyl methacrylate afforded low-polydispersity polymers (Mw/Mn ~1.2–1.4), with Mn values predicted to high conversions; where Mn and Mw are the number- and weight-average molecular weights respectively. This method is robust and would enhance the utility of RTCP.

Download Full-text

Reversible Chain Transfer Catalyzed Polymerization with Alkyl Iodides Generated from Alkyl Bromides by in Situ Halogen Exchange

Chinese Journal of Polymer Science ◽

10.1007/s10118-021-2611-2 ◽

2021 ◽

Author(s):

Dan-Ni Gao ◽

Yu-Lai Zhao ◽

Jing-Yu Cai ◽

Lin-Xi Hou ◽

Long-Qiang Xiao

Keyword(s):

Chain Transfer ◽

Alkyl Bromides ◽

Halogen Exchange ◽

Reversible Chain Transfer ◽

Alkyl Iodides ◽

Catalyzed Polymerization

Download Full-text

Synthesis of Poly(3-vinylpyridine)-Block-Polystyrene Diblock Copolymers via Surfactant-Free RAFT Emulsion Polymerization

Materials ◽

10.3390/ma12193145 ◽

2019 ◽

Vol 12 (19) ◽

pp. 3145 ◽

Cited By ~ 4

Author(s):

Katharina Nieswandt ◽

Prokopios Georgopanos ◽

Clarissa Abetz ◽

Volkan Filiz ◽

Volker Abetz

Keyword(s):

Emulsion Polymerization ◽

Self Assembly ◽

Diblock Copolymers ◽

Chain Transfer ◽

Raft Polymerization ◽

Free Water ◽

Monomer Conversion ◽

Molecular Weights ◽

Reversible Addition

In this work, we present a novel synthetic route to diblock copolymers based on styrene and 3-vinylpyridine monomers. Surfactant-free water-based reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization of styrene in the presence of the macroRAFT agent poly(3-vinylpyridine) (P3VP) is used to synthesize diblock copolymers with molecular weights of around 60 kDa. The proposed mechanism for the poly(3-vinylpyridine)-block-poly(styrene) (P3VP-b-PS) synthesis is the polymerization-induced self-assembly (PISA) which involves the in situ formation of well-defined micellar nanoscale objects consisting of a PS core and a stabilizing P3VP macroRAFT agent corona. The presented approach shows a well-controlled RAFT polymerization, allowing for the synthesis of diblock copolymers with high monomer conversion. The obtained diblock copolymers display microphase-separated structures according to their composition.

Download Full-text

Enhanced ‘in situ’ catalysis via microwave selective heating: catalytic chain transfer polymerisation

RSC Advances ◽

10.1039/c4ra00907j ◽

2014 ◽

Vol 4 (31) ◽

pp. 16172-16180 ◽

Cited By ~ 5

Author(s):

Kevin Adlington ◽

Robert McSweeney ◽

Georgios Dimitrakis ◽

Samuel W. Kingman ◽

John P. Robinson ◽

...

Keyword(s):

Microwave Heating ◽

Chain Transfer ◽

Active Catalyst ◽

Selective Heating ◽

Catalytic Chain Transfer ◽

Synthesis Methodology ◽

In Situ Catalysis

The formation of a CCTP active catalyst, which is promoted by adopting microwave heating and an “in situ” synthesis methodology.

Download Full-text

In-situ Titration of Initiator-Consuming Impurities in Solution Anionic Polymerization

Rubber Chemistry and Technology ◽

10.5254/1.3538331 ◽

1993 ◽

Vol 66 (4) ◽

pp. 588-593 ◽

Cited By ~ 10

Author(s):

V. M. Monroy ◽

G. Guevara ◽

I. Leon ◽

A. Correa ◽

R. Herrera

Keyword(s):

Anionic Polymerization ◽

Polymerization Reaction ◽

Molecular Weights

Abstract An in situ titration of initiator-consuming impurities in amonic polymerizations, using 1,10-phenantroline as an indicator, was developed. The results show that even when impurities are present, it is possible to destroy them prior to the initiation of the polymerization reaction and achieve a better control of molecular weights by adding accurate known quantities of initiator.

Download Full-text

Preparation of High-Purity Ammonium Tetrakis(pentafluorophenyl)borate for the Activation of Olefin Polymerization Catalysts

Molecules ◽

10.3390/molecules26092827 ◽

2021 ◽

Vol 26 (9) ◽

pp. 2827

Author(s):

Hyun-Ju Lee ◽

Jun-Won Baek ◽

Yeong-Hyun Seo ◽

Hong-Cheol Lee ◽

Sun-Mi Jeong ◽

...

Keyword(s):

Type Species ◽

Olefin Polymerization ◽

Bulk Polymerization ◽

Aliphatic Hydrocarbon ◽

Polymerization Catalysts ◽

Co Catalyst ◽

Co Catalysts ◽

Hydrocarbon Solvents ◽

In Situ Activation

Homogeneous olefin polymerization catalysts are activated in situ with a co-catalyst ([PhN(Me)2-H]+[B(C6F5)4]− or [Ph3C]+[B(C6F5)4]−) in bulk polymerization media. These co-catalysts are insoluble in hydrocarbon solvents, requiring excess co-catalyst (>3 eq). Feeding the activated species as a solution in an aliphatic hydrocarbon solvent may be advantageous over the in situ activation method. In this study, highly pure and soluble ammonium tetrakis(pentafluorophenyl)borates ([Me(C18H37)2N-H]+[B(C6F5)4]− and [(C18H37)2NH2]+[B(C6F5)4]−) containing neither water nor Cl− salt impurities were prepared easily via the acid–base reaction of [PhN(Me)2-H]+[B(C6F5)4]− and the corresponding amine. Using the prepared ammonium salts, the activation reactions of commercial-process-relevant metallocene (rac-[ethylenebis(tetrahydroindenyl)]Zr(Me)2 (1-ZrMe2), [Ph2C(Cp)(3,6-tBu2Flu)]Hf(Me)2 (3-HfMe2), [Ph2C(Cp)(2,7-tBu2Flu)]Hf(Me)2 (4-HfMe2)) and half-metallocene complexes ([(h5-Me4C5)Si(Me)2(k-NtBu)]Ti(Me)2 (5-TiMe2), [(h5-Me4C5)(C9H9(k-N))]Ti(Me)2 (6-TiMe2), and [(h5-Me3C7H1S)(C10H11(k-N))]Ti(Me)2 (7-TiMe2)) were monitored in C6D12 with 1H NMR spectroscopy. Stable [L-M(Me)(NMe(C18H37)2)]+[B(C6F5)4]− species were cleanly generated from 1-ZrMe2, 3-HfMe2, and 4-HfMe2, while the species types generated from 5-TiMe2, 6-TiMe2, and 7-TiMe2 were unstable for subsequent transformation to other species (presumably, [L-Ti(CH2N(C18H37)2)]+[B(C6F5)4]−-type species). [L-TiCl(N(H)(C18H37)2)]+[B(C6F5)4]−-type species were also prepared from 5-TiCl(Me) and 6-TiCl(Me), which were newly prepared in this study. The prepared [L-M(Me)(NMe(C18H37)2)]+[B(C6F5)4]−-, [L-Ti(CH2N(C18H37)2)]+[B(C6F5)4]−-, and [L-TiCl(N(H)(C18H37)2)]+[B(C6F5)4]−-type species, which are soluble and stable in aliphatic hydrocarbon solvents, were highly active in ethylene/1-octene copolymerization performed in aliphatic hydrocarbon solvents.

Download Full-text

Controlled (Co)Polymerization of Methacrylates Using a Novel Symmetrical Trithiocarbonate RAFT Agent Bearing Diphenylmethyl Groups

Molecules ◽

10.3390/molecules26154618 ◽

2021 ◽

Vol 26 (15) ◽

pp. 4618

Author(s):

Alvaro Leonel Robles Grana ◽

Hortensia Maldonado-Textle ◽

José Román Torres-Lubián ◽

Claude St Thomas ◽

Ramón Díaz de León ◽

...

Keyword(s):

Molecular Weight ◽

Chain Transfer ◽

Polymerization Process ◽

Polymerization Reaction ◽

Molecular Weights ◽

Molar Ratios ◽

Efficient Control ◽

Raft Agent ◽

Methacrylic Monomers ◽

Leaving Groups

Herein, we report a novel type of symmetrical trithiocarbonate chain transfer agent (CTA) based diphenylmethyl as R groups. The utilization of this CTA in the Reversible Addition-Fragmentation chain Transfer (RAFT) process reveals an efficient control in the polymerization of methacrylic monomers and the preparation of block copolymers. The latter are obtained by the (co)polymerization of styrene or butyl acrylate using a functionalized macro-CTA polymethyl methacrylate (PMMA) previously synthesized. Data show low molecular weight dispersity values (Đ < 1.5) particularly in the polymerization of methacrylic monomers. Considering a typical RAFT mechanism, the leaving groups (R) from the fragmentation of CTA should be able to re-initiate the polymerization (formation of growth chains) allowing an efficient control of the process. Nevertheless, in the case of the polymerization of MMA in the presence of this symmetrical CTA, the polymerization process displays an atypical behavior that requires high [initiator]/[CTA] molar ratios for accessing predictable molecular weights without affecting the Đ. Some evidence suggests that this does not completely behave as a common RAFT agent as it is not completely consumed during the polymerization reaction, and it needs atypical high molar ratios [initiator]/[CTA] to be closer to the predicted molecular weight without affecting the Đ. This work demonstrates that MMA and other methacrylic monomers can be polymerized in a controlled way, and with “living” characteristics, using certain symmetrical trithiocarbonates.

Download Full-text

A Photoactivatable α5β1-Specific Integrin Ligand

10.26434/chemrxiv.6097688 ◽

2018 ◽

Author(s):

Roshna Vakkeel ◽

Aleeza Farrukh ◽

Aranzazu del Campo

Keyword(s):

Cellular Response ◽

Light Exposure ◽

Matrix Composition ◽

Cellular Behavior ◽

Dynamic Variations ◽

In Situ Activation ◽

Controlled Exposure ◽

Cellular Behaviour ◽

Integrin Ligand

In order to study how dynamic changes of α5β1 integrin engagement affect cellular behaviour, photoactivatable derivatives of α5β1 specific ligands are presented in this article. The presence of the photoremovable protecting group (PRPG) introduced at a relevant position for integrin recognition, temporally inhibits ligand bioactivity. Light exposure at cell-compatible dose efficiently cleaves the PRPG and restores functionality. Selective cell response (attachment, spreading, migration) to the activated ligand on the surface is achieved upon controlled exposure. Spatial and temporal control of the cellular response is demonstrated, including the possibility to in situ activation. Photoactivatable integrin-selective ligands in model microenvironments will allow the study of cellular behavior in response to changes in the activation of individual integrins as consequence of dynamic variations of matrix composition.

Download Full-text