Exceptionally high molecular weight linear polyethylene by using N,N,N′‐Co catalysts appended with a N′‐2,6‐bis{di(4‐fluorophenyl)methyl}‐4‐nitrophenyl group

Abstract

The bis(arylimino)pyridines, 2‐[CMeN{2,6‐{(4‐FC6H4)2CH}2–4‐NO2}]‐6‐(CMeNAr)C5H3N (Ar = 2,6‐Me2C6H3 L1, 2,6‐Et2C6H3 L2, 2,6‐i‐Pr2C6H3 L3, 2,4,6‐Me3C6H2 L4, 2,6‐Et2–4‐MeC6H2 L5), each containing one N′‐2,6‐bis{di(4‐fluorophenyl)methyl}‐4‐nitrophenyl group, have been synthesized by two successive condensation reactions from 2,6‐diacetylpyridine. Their subsequent treatment with anhydrous cobalt (II) chloride gave the corresponding N,N,N′‐CoCl2 chelates, Co1 – Co5, in excellent yield. All five complexes have been characterized by 1H/19F NMR and IR spectroscopy as well as by elemental analysis. In addition, the molecular structures of Co1 and Co3 have been determined and help to emphasize the differences in steric properties imposed by the inequivalent N‐aryl groups; distorted square pyramidal geometries are adopted by each complex. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), precatalyts Co1 – Co5 collectively exhibited very high activities for ethylene polymerization with 2,6‐dimethyl‐substituted Co1 the most active (up to 1.1 × 107 g (PE) mol−1 (Co) h−1); the MAO systems were generally more productive. Linear polyethylenes of exceptionally high molecular weight (Mw up to 1.3 × 106 g mol−1) were obtained in all cases with the range in dispersities exhibited using MAO as co‐catalyst noticeably narrower than with MMAO [Mw/Mn: 3.55–4.77 (Co1 – Co5/MAO) vs. 2.85–12.85 (Co1 – Co5/MMAO)]. Significantly, the molecular weights of the polymers generated using this class of cobalt catalyst are higher than any literature values reported to date using related N,N,N‐bis (arylimino)pyridine‐cobalt catalysts.

Adjusting Ortho-Cycloalkyl Ring Size in a Cycloheptyl-Fused N,N,N-Iron Catalyst as Means to Control Catalytic Activity and Polyethylene Properties

“…As highlighted in Table 3 and Table 4, the melting points displayed by the polyethylenes fell between 126.4 and 135.1 °C, which is characteristic of linear polyethylene [32,35,37]. To confirm this assertion and gather more information about the end group composition and likely chain transfer 4); MAO used as the co-catalyst in each case.…”

“…The microanalytical data for all five complexes were consistent with compositions based on the general formula LFeCl 2 . In addition, their IR spectra revealed ν(C=N) imine-stretching frequencies at around 1600 cm −1 , wavenumbers that are typical for that seen in similar N,N,N-iron complexes [3][4][5][6][7][8][19][20][21][22][23][24][31][32][33][34].…”

“…In previous studies, precatalysts A-E (Scheme 1) exhibited their optimum performance for ethylene polymerization when activated with either modified methylaluminoxane (MMAO) or methylaluminoxane (MAO) [31][32][33]35]. Hence, this work is concerned with using both of these co-catalysts with Fe2 chosen as the test precatalyst to permit an optimization of the reaction parameters.…”

“…Hence, this work is concerned with using both of these co-catalysts with Fe2 chosen as the test precatalyst to permit an optimization of the reaction parameters. Changes to the run temperature, Al:Fe molar ratio, run time, and pressure will be independently undertaken for both Fe2/MMAO and Fe2/MAO before extending the corresponding set of optimized conditions to the remaining precatalysts, Fe1, Fe3, Fe4, and Fe5 [19][20][21][22][23][24]28,[31][32][33][34]. Typically, the polymerization runs will be performed in toluene at an ethylene pressure of 10 bar over a 30 min run time; the full set of data are collected in Tables 3 and 4.…”

Enhancing Ethylene Polymerization of NNN-Cobalt(II) Precatalysts Adorned with a Fluoro-substituent

“… 3 , 4 , 13 , 14 , 39 , 40 Therefore, our research group and others investigated the introduction of a range of steric hindrances and controlled the steric and electronic effects on the N-aryl group to improve the catalytic performance, as well as on the polymer properties. 6 , 8 , 10 − 12 , 17 Focusing on the cobalt precatalysts bearing unsymmetrical ligands incorporating double ortho -benzhydryl and a range of para-X groups (X = Me 6 , Cl 9 , NO 2 13 ) ( Chart 1 B ), as well as a single ortho -benzhydryl ( Chart 1 C ), 12 the modified precatalysts performed higher activities than prototypal precatalysts ( Chart 1 A ). 4 , 5 , 50 , 51 However, the cobalt precatalysts did not have good thermal stability.…”