Design of Ziegler-Natta catalyst modified with pore structure and preparation of UHMWPE with high impact resistance and low entanglement

doi:10.11949/0438-1157.20221460

Abstract

Abstract:

From the perspective of SiO₂ carrier channel modification, polystyrene (PS) and polysilsesquioxane (POSS) were simultaneously introduced into the multi-level channel to form a functional composite carrier, which was used to load TiCl₄ to prepare SiO₂/PS/POSS/TiCl₄ supported catalyst. Thermal gravimetric analysis, N₂ isothermal adsorption and desorption, scanning electron microscopy, and diffuse reflectance infrared spectroscopy were used to characterize the structures of the catalysts before and after the modification. It was found that it was possible to use in-situ polymerization of styrene to introduce PS into SiO₂ multistage pores, especially into the micropores, and that the swelling behavior of PS chain segments within the pores led to an increase in ethylene mass transfer resistance and a decrease in polymerization activity during polymerization. After introducing POSS into the SiO₂ multistage pore channel, it could only enter the SiO₂ macropores due to the sterichindrance of POSS molecules, where the reduction effect to the entanglenets of nascent of polyethylene was limited. A benign synergy for reducing the chain entanglements of nascent polyethylene was generated owing to the successive introduction of PS and POSS into the catalyst pores. The impact strength of the synthesized polyethylene was greatly enhanced. Finally, the catalyst active center was further diluted through reducing the loading of TiCl₄ in the pore channel, where the untwining process of the propagated polyethylene chain was further strengthened. The optimum polymerization activity, the highest impact strength of the synthesized polyethylene were achieved when the titanium content was reduced to 2.65%.

Key words: Ziegler-Natta catalyst, polyethylene, impact properties, chain entanglement, process intensification

摘要：

从SiO₂载体孔道修饰的角度出发，向多级孔道中同时引入聚苯乙烯（PS）和聚倍半硅氧烷（POSS），形成功能化复合载体，并用于负载TiCl₄，制备SiO₂/PS/POSS/TiCl₄负载型催化剂。采用热重分析、N₂等温吸附脱附、扫描电镜、漫反射红外光谱等手段对修饰前后催化剂的结构进行表征，发现利用苯乙烯的原位聚合能够向SiO₂多级孔道，尤其是微孔中引入PS，孔道内 PS链段的溶胀行为导致聚合时乙烯传质阻力增大，聚合活性降低。向SiO₂多级孔道中引入POSS，由于POSS分子的空间位阻，其只能进入SiO₂大孔中，初生态聚乙烯分子链缠结程度降低有限。而将PS与POSS共同引入催化剂各级孔道中，PS与POSS能够产生良性协同作用，能够以高活性制备低缠结的超高分子量聚乙烯，显著提升了产品的抗冲击强度。最后通过降低孔道内TiCl₄的负载量，进一步稀释催化剂活性中心，实现聚乙烯活性链解缠结的过程强化。当钛含量降至2.65%时，聚合活性、抗冲击强度和链缠结程度均达到最佳。

关键词: Ziegler-Natta催化剂, 聚乙烯, 冲击性能, 链缠结, 过程强化

CLC Number:

TQ 322.2

Qian LIU, Yu CAO, Qi ZHOU, Jingshan MU, Wei LI. Design of Ziegler-Natta catalyst modified with pore structure and preparation of UHMWPE with high impact resistance and low entanglement[J]. CIESC Journal, 2023, 74(3): 1092-1101.

刘倩, 曹禹, 周琦, 穆景山, 历伟. 孔道结构修饰的Ziegler-Natta催化剂设计与高抗冲低缠结UHMWPE的制备[J]. 化工学报, 2023, 74(3): 1092-1101.

Figures/Tables 11

Fig.1 The mass loss curve，the N2 adsorption isotherms，the pore size distribution， and the FTIR spectra of supports

Table 1 Pore size parameters of composite supporters

Supports	Pore size /nm	Surface area /（cm²·g^-1）	Pore volume /（cm³·g^-1）
SiO₂	24.99	204.12	1.74
SiO₂/PS	23.77	201.28	1.51
SiO₂/POSS	20.67	206.24	1.23
SiO₂/PS/POSS	19.26	202.61	1.10

Fig.2 The SEM images of SiO2, SiO2/PS, SiO2/POSS and SiO2/PS/POSS support

Table 2 XPS analysis results of catalysts modified by PS or POSS

Catalyst	Ti(Ⅳ) 2p_1/2		Ti(Ⅳ) 2p_3/2		Mg 2p
Catalyst	BE/eV	FWHM/eV	BE/eV	FWHM/eV	BE/eV	FWHM/eV
SiO₂/TiCl₄	464.27	3.32	459.21	2.92	51.06	2.88
SiO₂/POSS/TiCl₄	465.03	3.21	459.35	2.83	51.15	2.72
SiO₂/PS/TiCl₄	464.39	3.33	459.25	2.97	51.08	2.89
SiO₂/PS/POSS/TiCl₄	465.07	3.14	459.39	2.78	51.20	2.69

Table 3 The results of ethylene polymerization

Samples	Ti/ %(mass)	Act/ (10⁶ g PE⋅ (mol Ti·h)^-1)	Bulk density/ (g·cm^-3)	$T m 1 / ℃$	$T m 2 / ℃$	$X c 1 / %$	$X c 2 / %$	M_η / (10⁶ g·mol^-1)	MWD	M_w/ (10⁶ g·mol^-1)
PE-SiO₂/TiCl₄	5.43	2.83	0.30	144.38	137.85	69.12	56.51	1.84	2.5	0.53
PE-SiO₂/POSS/TiCl₄	4.82	3.03	0.31	144.01	137.68	68.35	57.32	2.09	2.6	0.64
PE-SiO₂/PS/TiCl₄	5.31	2.47	0.33	144.31	137.51	67.26	58.41	2.72	2.8	0.82
PE-SiO₂/PS/POSS/TiCl₄	4.54	3.28	0.32	145.08	138.16	70.12	59.02	3.47	3.0	1.25
PE-SiO₂/PS/POSS/TiCl₄-reduce the loading content
Cat-TiCl₄-10 ml	4.54	3.28	0.32	145.08	138.16	70.12	59.02	3.47	3.0	1.25
Cat-TiCl₄-8 ml	3.66	4.77	0.35	144.78	137.91	71.95	61.3	3.48	3.0	1.27
Cat-TiCl₄-6 ml	2.65	5.39	0.37	144.80	137.04	71.20	60.05	3.64	3.1	1.32
Cat-TiCl₄-4 ml	1.68	3.70	0.33	144.54	137.79	70.05	58.95	3.50	3.1	1.28
UHMWPE	—	—	0.33	144.43	137.32	58.26	45.01	3.50	2.9	1.31

Table 3 The results of ethylene polymerization

Samples	Ti/ %(mass)	Act/ (10⁶ g PE⋅ (mol Ti·h)^-1)	Bulk density/ (g·cm^-3)	$T m 1 / ℃$	$T m 2 / ℃$	$X c 1 / %$	$X c 2 / %$	M_η / (10⁶ g·mol^-1)	MWD	M_w/ (10⁶ g·mol^-1)
PE-SiO₂/TiCl₄	5.43	2.83	0.30	144.38	137.85	69.12	56.51	1.84	2.5	0.53
PE-SiO₂/POSS/TiCl₄	4.82	3.03	0.31	144.01	137.68	68.35	57.32	2.09	2.6	0.64
PE-SiO₂/PS/TiCl₄	5.31	2.47	0.33	144.31	137.51	67.26	58.41	2.72	2.8	0.82
PE-SiO₂/PS/POSS/TiCl₄	4.54	3.28	0.32	145.08	138.16	70.12	59.02	3.47	3.0	1.25
PE-SiO₂/PS/POSS/TiCl₄-reduce the loading content
Cat-TiCl₄-10 ml	4.54	3.28	0.32	145.08	138.16	70.12	59.02	3.47	3.0	1.25
Cat-TiCl₄-8 ml	3.66	4.77	0.35	144.78	137.91	71.95	61.3	3.48	3.0	1.27
Cat-TiCl₄-6 ml	2.65	5.39	0.37	144.80	137.04	71.20	60.05	3.64	3.1	1.32
Cat-TiCl₄-4 ml	1.68	3.70	0.33	144.54	137.79	70.05	58.95	3.50	3.1	1.28
UHMWPE	—	—	0.33	144.43	137.32	58.26	45.01	3.50	2.9	1.31

Fig.3 Products characterization of catalysts modified by PS and POSS

Table 4 XPS analysis results of catalysts with different titanium contents

Ti content/%	Ti(Ⅳ) 2p_1/2		Ti(Ⅳ) 2p_3/2		Mg 2p
Ti content/%	BE/ eV	FWHM/eV	BE/ eV	FWHM/eV	BE/ eV	FWHM/eV
4.27	465.15	3.02	459.35	2.51	51.30	2.48
3.66	465.15	2.97	459.37	2.48	51.50	2.33
2.65	465.24	2.78	459.39	2.31	51.69	2.28
1.68	465.13	2.67	459.35	2.29	51.19	2.18

Fig.4 XPS analysis results of catalysts with different titanium contents

Fig.5 The SEM images of polyethylene products with different catalysts

Table 5 Mechanical properties of disentanglement polyethylene

Ti content/%	F_max^①/MPa	YM^②/MPa	ε^③/%	Izod^④/(kJ·m^-2)
4.27	27.5±2.6	386.7±46.0	569.7±73.0	108.0±0.8
3.66	27.2±0.9	394.5±62.0	535.8±52.0	110.2±2.2
2.65	31.0±1.5	385.2±47.0	474.3±44.0	116.6±5.5
1.68	32.0±2.2	365.2±47.0	444.3±44.0	108.6±5.5

Fig.6 Characterization of catalyst products with different Ti contents

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