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Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path

Copolymerization of ethylene (E) with 5-vinyl-2-norbornene (VNB) catalyzed by ansa-metallocenes allows the precise control of essential polymeric properties such as comonomer incorporation, molecular weight (M(w)), and polydispersity (Đ). Significant efforts have been devoted to synthesizing and dev...

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Autores principales: Ali, Amjad, Naveed, Ahmad, Shehzad, Khurram, Aziz, Tariq, Rasheed, Tahir, Moradian, Jamile Mohammadi, Hassan, Mobashar, Rahman, Abdul, Zhiqiang, Fan, Guo, Li
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Royal Society of Chemistry 2022
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9118019/
https://www.ncbi.nlm.nih.gov/pubmed/35693231
http://dx.doi.org/10.1039/d2ra01264b
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author Ali, Amjad
Naveed, Ahmad
Shehzad, Khurram
Aziz, Tariq
Rasheed, Tahir
Moradian, Jamile Mohammadi
Hassan, Mobashar
Rahman, Abdul
Zhiqiang, Fan
Guo, Li
author_facet Ali, Amjad
Naveed, Ahmad
Shehzad, Khurram
Aziz, Tariq
Rasheed, Tahir
Moradian, Jamile Mohammadi
Hassan, Mobashar
Rahman, Abdul
Zhiqiang, Fan
Guo, Li
author_sort Ali, Amjad
collection PubMed
description Copolymerization of ethylene (E) with 5-vinyl-2-norbornene (VNB) catalyzed by ansa-metallocenes allows the precise control of essential polymeric properties such as comonomer incorporation, molecular weight (M(w)), and polydispersity (Đ). Significant efforts have been devoted to synthesizing and developing novel catalysts, cocatalysts, and activators, although the fundamental elements of catalytic processes remain unclear. For example, it is questionable how polymeric catalysts are divided across dormant and active sites and how this distribution affects the order of monomers for the propagation rate, which widely vary in the literature. Furthermore, although the empirical correlation between the monomers and average M(w) has been established in many systems, the fundamental processes of chain termination remain unknown. Furthermore, the involvement of ion-pairing in metallocene-catalyzed polymerization and the termination mechanisms are also contentious issues. In this study, we describe the use of a quenched-labeling technique based on acyl chloride to selectively quench the zirconium metal–polymeric bond, which can be used to study the kinetics, active site [Zr][C*] counting, copolymer microstructure, and molecular weight distribution (MWD) to determine the rate laws for chain initiation, chain propagation rate (R(p)), propagation rate constant (k(p)) and chain termination. In addition, we also predict previously unknown chemical characteristics of E/bicyclic copolymerization processes, where either a cis-endocyclic double bond with steric properties or a vinyl exocyclic double bond affects the activity, i.e., [Zr]/[*C], (R(p)) and (k(p)). All these properties require the implementation of a particular kinetic mechanism that assumes the low activity of the building copolymer chains incorporating a single ethylene/VNB unit, i.e., the Cp(2)Zr–C(2)H(5) group, in the ethylene addition process in the Cp(2)Zr–C bond. Due to β-agostic stabilization, the Cp(2)Zr–C(2)H(5) group exhibits a distinct feature. These effects were confirmed experimentally, such as the E/VNB co-polymer activity and VNB mol%, propagation rate decrease in the polymerization time (t(p)) of 120 s to 1800 s, crystalline properties, and significant increase in molecular weight. The active center [Zr]/[*C] fraction considerably increased in the initial (t(p)) 840 s, and subsequently tended to the steady stage of 33%, which is lower than previously reported E homo- and E/P copolymerization. The lower [C*]/[Zr] in both the early and stable stages, decrease in VNB mol%, and R(p) with t(p) can be associated with the more significant fraction of Cp(2)Zr–CH(2)CH(3)-type dormant site by the β-agostic hydrogen interaction with the Cp(2)Zr metal. The t(p)versus R(p)E, R(p)VNB, k(p)E, k(p)VNB, and [Zr]/[C*] count could be fitted to a model that invokes deactivation of the growing polymer chains. In the case of the thermal behavior of the copolymers (melting temperature (T(m)) and crystalline temperature (ΔH(m))), T(m) varied from 101 °C to 121 °C, while ΔH(m) varied from 9 to 16 (J g(−1)).
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spelling pubmed-91180192022-06-10 Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path Ali, Amjad Naveed, Ahmad Shehzad, Khurram Aziz, Tariq Rasheed, Tahir Moradian, Jamile Mohammadi Hassan, Mobashar Rahman, Abdul Zhiqiang, Fan Guo, Li RSC Adv Chemistry Copolymerization of ethylene (E) with 5-vinyl-2-norbornene (VNB) catalyzed by ansa-metallocenes allows the precise control of essential polymeric properties such as comonomer incorporation, molecular weight (M(w)), and polydispersity (Đ). Significant efforts have been devoted to synthesizing and developing novel catalysts, cocatalysts, and activators, although the fundamental elements of catalytic processes remain unclear. For example, it is questionable how polymeric catalysts are divided across dormant and active sites and how this distribution affects the order of monomers for the propagation rate, which widely vary in the literature. Furthermore, although the empirical correlation between the monomers and average M(w) has been established in many systems, the fundamental processes of chain termination remain unknown. Furthermore, the involvement of ion-pairing in metallocene-catalyzed polymerization and the termination mechanisms are also contentious issues. In this study, we describe the use of a quenched-labeling technique based on acyl chloride to selectively quench the zirconium metal–polymeric bond, which can be used to study the kinetics, active site [Zr][C*] counting, copolymer microstructure, and molecular weight distribution (MWD) to determine the rate laws for chain initiation, chain propagation rate (R(p)), propagation rate constant (k(p)) and chain termination. In addition, we also predict previously unknown chemical characteristics of E/bicyclic copolymerization processes, where either a cis-endocyclic double bond with steric properties or a vinyl exocyclic double bond affects the activity, i.e., [Zr]/[*C], (R(p)) and (k(p)). All these properties require the implementation of a particular kinetic mechanism that assumes the low activity of the building copolymer chains incorporating a single ethylene/VNB unit, i.e., the Cp(2)Zr–C(2)H(5) group, in the ethylene addition process in the Cp(2)Zr–C bond. Due to β-agostic stabilization, the Cp(2)Zr–C(2)H(5) group exhibits a distinct feature. These effects were confirmed experimentally, such as the E/VNB co-polymer activity and VNB mol%, propagation rate decrease in the polymerization time (t(p)) of 120 s to 1800 s, crystalline properties, and significant increase in molecular weight. The active center [Zr]/[*C] fraction considerably increased in the initial (t(p)) 840 s, and subsequently tended to the steady stage of 33%, which is lower than previously reported E homo- and E/P copolymerization. The lower [C*]/[Zr] in both the early and stable stages, decrease in VNB mol%, and R(p) with t(p) can be associated with the more significant fraction of Cp(2)Zr–CH(2)CH(3)-type dormant site by the β-agostic hydrogen interaction with the Cp(2)Zr metal. The t(p)versus R(p)E, R(p)VNB, k(p)E, k(p)VNB, and [Zr]/[C*] count could be fitted to a model that invokes deactivation of the growing polymer chains. In the case of the thermal behavior of the copolymers (melting temperature (T(m)) and crystalline temperature (ΔH(m))), T(m) varied from 101 °C to 121 °C, while ΔH(m) varied from 9 to 16 (J g(−1)). The Royal Society of Chemistry 2022-05-19 /pmc/articles/PMC9118019/ /pubmed/35693231 http://dx.doi.org/10.1039/d2ra01264b Text en This journal is © The Royal Society of Chemistry https://creativecommons.org/licenses/by-nc/3.0/
spellingShingle Chemistry
Ali, Amjad
Naveed, Ahmad
Shehzad, Khurram
Aziz, Tariq
Rasheed, Tahir
Moradian, Jamile Mohammadi
Hassan, Mobashar
Rahman, Abdul
Zhiqiang, Fan
Guo, Li
Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path
title Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path
title_full Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path
title_fullStr Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path
title_full_unstemmed Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path
title_short Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path
title_sort polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9118019/
https://www.ncbi.nlm.nih.gov/pubmed/35693231
http://dx.doi.org/10.1039/d2ra01264b
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