Enhancement on Nickel-Mediated Ethylene Polymerization by Concerted Steric Hindrance and Fluorine Effect

doi:10.6023/A22020066

Abstract

Olefin polymerization is one of the most important chemical reactions in industry. Transition metal catalysts are the key to the development of olefin polymerization. Neutral salicylaldiminato nickel catalyst stands out due to the nature of both functional-group tolerance and cocatalyst-free. Either sterically hindered effect or fluorine effect has extensively been reported over the past decades to improve properties of neutral and single-component salicylaldiminato nickel catalyst; however, combination of these two effects to generate a concerted strategy is much less studied. In this work, both para-sterically hindered substituents including phenyl, 1-naphthyl or 9-anthracenyl group and ortho-fluorine substituents are concurrently installed into salicylaldimine ligands, and thus five salicylaldiminato nickel catalysts have been synthesized and fully identified by ¹H and ¹³C NMR spectroscopy, elemental analysis and X-ray diffraction technique if possible. Without the addition of any activator, these single-component nickel catalysts are used to ethylene polymerization. Influence of sterically hindered effect, fluorine effect, reaction temperature and reaction time on catalytic activity, polymer molecular weight, and branching density of polymer is comprehensively investigated. ortho-Fluorine substituents particularly elevate catalytic activity, lifetime of catalyst species, and polymer molecular weight, while decreases branching density of polymer. Enhancement of catalytic activity and polymer molecular weight reaches two orders of magnitude and 36 times, respectively; and linear structure (5 branches/1000 carbon) of polyethylene can be accessible. This should originate from the inhibition of both chain transfer and chain walking pathways. The bulk of para-sterically hindered substituents can be designed according to the required catalytic activity and molecular weight, and notably it has a minor influence on branching density of polymer. The concerted combination of fluorine effect and steric shielding effect enables the formation of linear ultrahigh molecular weight polyethylene (UHMWPE). This work develops a new strategy for the efficient design of salicylaldiminato nickel olefin polymerization catalyst.

Key words: olefin polymerization, fluorine effect, steric hindrance, nickel catalyst, salicylaldimine

Cite this article

Yuyin Wang, Xiaoqiang Hu, Hongliang Mu, Yan Xia, Yue Chi, Zhongbao Jian. Enhancement on Nickel-Mediated Ethylene Polymerization by Concerted Steric Hindrance and Fluorine Effect[J]. Acta Chimica Sinica, 2022, 80(6): 741-747.

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Entry	Cat.	T/℃	Yield/g	Act.^b/(×10⁶)	M_n ^c/(×10⁴)	M_w^c/(×10⁴)	M_w/M_n ^c	Brs ^d	T_m^e/℃	Chain/[Ni]
1	Ni1	30	2.31	9.24	44.4	81.1	1.83	2	133.8	10.4
2	Ni1	40	3.59	14.36	15.3	35.5	2.32	3	131.1	46.9
3	Ni1	50	9.40	37.60	6.6	18.7	2.85	9	130.8	284.8
4	Ni2	30	1.39	5.56	64.2	131.3	2.04	3	133.3	4.3
5	Ni2	40	2.45	9.80	29.7	65.2	2.19	4	133.6	16.5
6	Ni2	50	5.56	22.24	8.5	21.5	2.52	5	128.6	130.8
7	Ni3	30	3.61	14.44	53.7	114.6	2.13	3	133.7	13.4
8	Ni3	40	4.61	18.44	21.3	41.9	2.06	4	133.1	43.3
9	Ni3	50	5.76	23.04	8.8	21.5	2.44	8	129.7	130.9
10	Ni4	30	3.63	14.52	54.2	112.4	2.07	5	133.3	13.4
11	Ni4	40	1.59	6.36	22.3	53.2	2.39	5	133.5	14.3
12	Ni4	50	1.29	5.16	10.2	22.5	2.21	7	128.1	25.3
13	Ni4'	30	0.05	0.20	1.5	3.8	2.52	26	106.3	6.7
14	Ni4'	40	0.01	0.05	0.8	1.9	2.33	34	103.3	2.5
15	Ni4'	50	trace	—	—	—	—	—	—	—

Entry	Cat.	T/℃	Yield/g	Act.^b/(×10⁶)	M_n ^c/(×10⁴)	M_w^c/(×10⁴)	M_w/M_n ^c	Brs ^d	T_m^e/℃	Chain/[Ni]
1	Ni1	30	2.31	9.24	44.4	81.1	1.83	2	133.8	10.4
2	Ni1	40	3.59	14.36	15.3	35.5	2.32	3	131.1	46.9
3	Ni1	50	9.40	37.60	6.6	18.7	2.85	9	130.8	284.8
4	Ni2	30	1.39	5.56	64.2	131.3	2.04	3	133.3	4.3
5	Ni2	40	2.45	9.80	29.7	65.2	2.19	4	133.6	16.5
6	Ni2	50	5.56	22.24	8.5	21.5	2.52	5	128.6	130.8
7	Ni3	30	3.61	14.44	53.7	114.6	2.13	3	133.7	13.4
8	Ni3	40	4.61	18.44	21.3	41.9	2.06	4	133.1	43.3
9	Ni3	50	5.76	23.04	8.8	21.5	2.44	8	129.7	130.9
10	Ni4	30	3.63	14.52	54.2	112.4	2.07	5	133.3	13.4
11	Ni4	40	1.59	6.36	22.3	53.2	2.39	5	133.5	14.3
12	Ni4	50	1.29	5.16	10.2	22.5	2.21	7	128.1	25.3
13	Ni4'	30	0.05	0.20	1.5	3.8	2.52	26	106.3	6.7
14	Ni4'	40	0.01	0.05	0.8	1.9	2.33	34	103.3	2.5
15	Ni4'	50	trace	—	—	—	—	—	—	—

Entry	Cat.	t/min	Yield/g	Act.^b/×10⁶	M_n^c/10⁴	M_w/M_n^c	Brs ^d	T_m^e/℃
1	Ni2	15	0.89	3.56	20.8	2.27	4	131.0
2	Ni2	30	2.01	4.02	26.2	2.00	5	131.5
3	Ni2	60	2.42	2.42	30.0	2.19	4	132.6
4	Ni4	15	0.92	3.68	9.5	2.13	7	127.0
5	Ni4	30	2.42	4.84	13.7	1.96	6	128.1
6	Ni4	60	2.97	2.97	19.9	1.82	6	130.9
7^f	Ni4'	15	0.19	0.15	1.1	2.28	35	102.7
8^f	Ni4'	30	0.25	0.10	1.1	2.44	35	102.0
9^f	Ni4'	60	0.27	0.05	1.1	2.22	36	103.9

Entry	Cat.	t/min	Yield/g	Act.^b/×10⁶	M_n^c/10⁴	M_w/M_n^c	Brs ^d	T_m^e/℃
1	Ni2	15	0.89	3.56	20.8	2.27	4	131.0
2	Ni2	30	2.01	4.02	26.2	2.00	5	131.5
3	Ni2	60	2.42	2.42	30.0	2.19	4	132.6
4	Ni4	15	0.92	3.68	9.5	2.13	7	127.0
5	Ni4	30	2.42	4.84	13.7	1.96	6	128.1
6	Ni4	60	2.97	2.97	19.9	1.82	6	130.9
7^f	Ni4'	15	0.19	0.15	1.1	2.28	35	102.7
8^f	Ni4'	30	0.25	0.10	1.1	2.44	35	102.0
9^f	Ni4'	60	0.27	0.05	1.1	2.22	36	103.9

空间位阻与氟效应协同增强镍系乙烯聚合