Styrene Polymerization Behavior of Phenoxy−Imine Ligated Ti Complexes/MAO: Formation of Highly Isotactic and Syndiotactic PS

Abstract

Unique styrene polymerization behavior of bis(phenoxy-imine) Ti complexes (Ti-FI catalysts) combined with dried MAO (DMAO) was revealed. Upon activation with DMAO at 20 °C, non-fluorinated Ti-FI catalysts 1 and 2 produce highly syndiotactic polystyrene (sPS, T m 275 °C (1), 279 °C (2)), whereas fluorinated Ti-FI catalysts 3 and 4 form highly isotactic PS (iPS, T m 224 °C (3), 213 °C (4)). Interestingly, the fluorinated Ti-FI catalysts can produce an iPS/sPS mixture by varying polymerization conditions.

Stereospecific Styrene Polymerization by Methylalumoxane‐Activated Ti (IV) N‐Trimethylsilylamido Complexes Bearing the N‐Biphenyl or N‐(6‐(2‐(Diethylboryl)phenyl)‐Pyrid‐2‐yl) Motif

“…The aminoborane‐free complexes 7 / MAO and 8 / MAO showed much better performance in terms of catalytic activity than the 3 / MAO and 4 / MAO systems. Nonetheless, all systems 3 , 4 , 7 , and 8 by far outperform the more recently reported Ti‐phenoxyimine‐based pre‐catalysts and rival Kaminsky's (2‐methylbenz[e]indenyl)TiCl 3 /MAO system both in terms of molecular weights and PDIs . Thus, the observed number‐average molecular weights () of the resulting st‐ PS derived from non‐bridged half‐titanocenes increased in the order of 8 > 4 > 7 > 3 .…”

Stereospecific Styrene Polymerization by Methylalumoxane‐Activated Ti (IV) N‐Trimethylsilylamido Complexes Bearing the N‐Biphenyl or N‐(6‐(2‐(Diethylboryl)phenyl)‐Pyrid‐2‐yl) Motif

“…The aminoborane‐free complexes 7 / MAO and 8 / MAO showed much better performance in terms of catalytic activity than the 3 / MAO and 4 / MAO systems. Nonetheless, all systems 3 , 4 , 7 , and 8 by far outperform the more recently reported Ti‐phenoxyimine‐based pre‐catalysts and rival Kaminsky's (2‐methylbenz[e]indenyl)TiCl 3 /MAO system both in terms of molecular weights and PDIs . Thus, the observed number‐average molecular weights () of the resulting st‐ PS derived from non‐bridged half‐titanocenes increased in the order of 8 > 4 > 7 > 3 .…”

Mechanism of Isotactic Styrene Polymerization with a C6F5-Substituted Bis(phenoxyimine) Titanium System

“…The acquisition time of the 13 C NMR spectrum of Figure is 4 days. This long acquisition time allowed us to detect the resonances relative to the chain-end groups and to the stereoerrors which were below the NMR detection level in the 13 C NMR spectrum previously reported . The more detailed 13 C NMR spectrum reveals main resonances diagnostic of the iPS monomer units ( e.g ., a and b in Figure ), and additional less intense resonances attributable, according to the literature, , to unsaturated chain-end groups such as trans 1,3-diphenyl-1-butenyl group (Figure S1 of Supporting Information).…”

Bis(phenoxy-azo)titanium(IV) Complexes: Synthesis, Structure, and Catalytic Activity in Styrene Polymerization

“…When dry methylaluminoxane (DMAO) was mixed with 3b before the addition of styrene, the polymerization activity was greatly increased (Table , entries 2–4). The produced polystyrene was mainly syndiotactic, showing the same stereoselectivity for 3a , b as for the related phenoxy-imine complex 1b . However, a small amount of isotactic sequence was also observed by 1 H NMR when using 3b (entries 2 and 3), which was not obtained from 1b and 3a under the premix conditions (entries 1 and 5).…”

“…The produced polystyrene was mainly syndiotactic, showing the same stereoselectivity for 3a,b as for the related phenoxy-imine complex 1b. 13 However, a small amount of isotactic sequence was also observed by 1 H NMR when using 3b (entries 2 and 3), which was not obtained from 1b and 3a under the premix conditions (entries 1 and 5). 1 H NMR analysis of the mixture of 3b and 50 equiv of DMAO in toluene-d 8 showed broad signals with a single set of downfieldshifted ligand signals, indicating that both phenoxyazo aluminum and low-oxidation-state titanium complexes were generated.…”

Stereospecific Styrene Polymerization by Methylalumoxane‐Activated Ti (IV) N‐Trimethylsilylamido Complexes Bearing the N‐Biphenyl or N‐(6‐(2‐(Diethylboryl)phenyl)‐Pyrid‐2‐yl) Motif

“…The aminoborane‐free complexes 7 / MAO and 8 / MAO showed much better performance in terms of catalytic activity than the 3 / MAO and 4 / MAO systems. Nonetheless, all systems 3 , 4 , 7 , and 8 by far outperform the more recently reported Ti‐phenoxyimine‐based pre‐catalysts and rival Kaminsky's (2‐methylbenz[e]indenyl)TiCl 3 /MAO system both in terms of molecular weights and PDIs . Thus, the observed number‐average molecular weights () of the resulting st‐ PS derived from non‐bridged half‐titanocenes increased in the order of 8 > 4 > 7 > 3 .…”

Mechanism of Isotactic Styrene Polymerization with a C6F5-Substituted Bis(phenoxyimine) Titanium System

“…The acquisition time of the 13 C NMR spectrum of Figure is 4 days. This long acquisition time allowed us to detect the resonances relative to the chain-end groups and to the stereoerrors which were below the NMR detection level in the 13 C NMR spectrum previously reported . The more detailed 13 C NMR spectrum reveals main resonances diagnostic of the iPS monomer units ( e.g ., a and b in Figure ), and additional less intense resonances attributable, according to the literature, , to unsaturated chain-end groups such as trans 1,3-diphenyl-1-butenyl group (Figure S1 of Supporting Information).…”

Bis(phenoxy-azo)titanium(IV) Complexes: Synthesis, Structure, and Catalytic Activity in Styrene Polymerization

“…When dry methylaluminoxane (DMAO) was mixed with 3b before the addition of styrene, the polymerization activity was greatly increased (Table , entries 2–4). The produced polystyrene was mainly syndiotactic, showing the same stereoselectivity for 3a , b as for the related phenoxy-imine complex 1b . However, a small amount of isotactic sequence was also observed by 1 H NMR when using 3b (entries 2 and 3), which was not obtained from 1b and 3a under the premix conditions (entries 1 and 5).…”

“…The produced polystyrene was mainly syndiotactic, showing the same stereoselectivity for 3a,b as for the related phenoxy-imine complex 1b. 13 However, a small amount of isotactic sequence was also observed by 1 H NMR when using 3b (entries 2 and 3), which was not obtained from 1b and 3a under the premix conditions (entries 1 and 5). 1 H NMR analysis of the mixture of 3b and 50 equiv of DMAO in toluene-d 8 showed broad signals with a single set of downfieldshifted ligand signals, indicating that both phenoxyazo aluminum and low-oxidation-state titanium complexes were generated.…”

Stereospecific Styrene Polymerization by Methylalumoxane‐Activated Ti (IV) N‐Trimethylsilylamido Complexes Bearing the N‐Biphenyl or N‐(6‐(2‐(Diethylboryl)phenyl)‐Pyrid‐2‐yl) Motif

“…The aminoborane‐free complexes 7 / MAO and 8 / MAO showed much better performance in terms of catalytic activity than the 3 / MAO and 4 / MAO systems. Nonetheless, all systems 3 , 4 , 7 , and 8 by far outperform the more recently reported Ti‐phenoxyimine‐based pre‐catalysts and rival Kaminsky's (2‐methylbenz[e]indenyl)TiCl 3 /MAO system both in terms of molecular weights and PDIs . Thus, the observed number‐average molecular weights () of the resulting st‐ PS derived from non‐bridged half‐titanocenes increased in the order of 8 > 4 > 7 > 3 .…”

Mechanism of Isotactic Styrene Polymerization with a C6F5-Substituted Bis(phenoxyimine) Titanium System

“…The acquisition time of the 13 C NMR spectrum of Figure is 4 days. This long acquisition time allowed us to detect the resonances relative to the chain-end groups and to the stereoerrors which were below the NMR detection level in the 13 C NMR spectrum previously reported . The more detailed 13 C NMR spectrum reveals main resonances diagnostic of the iPS monomer units ( e.g ., a and b in Figure ), and additional less intense resonances attributable, according to the literature, , to unsaturated chain-end groups such as trans 1,3-diphenyl-1-butenyl group (Figure S1 of Supporting Information).…”

Bis(phenoxy-azo)titanium(IV) Complexes: Synthesis, Structure, and Catalytic Activity in Styrene Polymerization

“…When dry methylaluminoxane (DMAO) was mixed with 3b before the addition of styrene, the polymerization activity was greatly increased (Table , entries 2–4). The produced polystyrene was mainly syndiotactic, showing the same stereoselectivity for 3a , b as for the related phenoxy-imine complex 1b . However, a small amount of isotactic sequence was also observed by 1 H NMR when using 3b (entries 2 and 3), which was not obtained from 1b and 3a under the premix conditions (entries 1 and 5).…”

“…The produced polystyrene was mainly syndiotactic, showing the same stereoselectivity for 3a,b as for the related phenoxy-imine complex 1b. 13 However, a small amount of isotactic sequence was also observed by 1 H NMR when using 3b (entries 2 and 3), which was not obtained from 1b and 3a under the premix conditions (entries 1 and 5). 1 H NMR analysis of the mixture of 3b and 50 equiv of DMAO in toluene-d 8 showed broad signals with a single set of downfieldshifted ligand signals, indicating that both phenoxyazo aluminum and low-oxidation-state titanium complexes were generated.…”