POSS-modified supported Ziegler-Natta catalyst and its ethylene /1-hexene copolymerization

doi:10.11949/0438-1157.20201036

Abstract

Abstract:

Macroporous SiO₂ (Macro-SiO₂) with an open framework structure and MgCl₂ are used to form a composite carrier, and polysilsesquioxane (POSS) is introduced to form a spatially separated POSS/ MgCl₂ nano-aggregate, which is prepared after loading TiCl₄ modified Ziegler-Natta catalyst. The catalytic structure of POSS-free and modified catalysts was investigated by FTIR, TG, CO low-temperature IR spectroscopy, SEM and particle size analysis. The incorporated POSS contributed the formation of defect Mg_4c²⁺ sites and Lewis acidic sites, where the more defect Mg sites facilitated the effective loading of TiCl₄. The POSS-modified Ziegler-Natta catalyst exhibited exceptional activity reaching 1.03×10⁶ g?(mol·h)^-1 in ethylene/1-hexene copolymerization. Simultaneously, the ethylene-hexene copolymer with much higher comonomer contents (3.79%) and narrowed molecular weight distribution (MWD=3—6) was synthesized in the POSS modified catalyst.

Key words: Ziegler-Natta catalyst, Macro-SiO₂, POSS, ethylene, 1-hexene, copolymerization

摘要：

采用具有开放型骨架结构的大孔SiO₂（Macro-SiO₂）与MgCl₂形成复合载体，同时引入聚倍半硅氧烷（POSS）形成具有空间分隔作用的POSS/MgCl₂纳米团聚体，负载TiCl₄后制备得到改性Ziegler-Natta催化剂。采用红外分析、热重分析、CO低温吸附红外、扫描电镜、粒径分析等手段对POSS改性前后催化剂的结构进行表征，发现POSS的引入能诱导MgCl₂形成更多Mg_4c²⁺缺陷位点，并促进了Lewis酸性位点的形成，有利于TiCl₄有效活性中心的负载。乙烯/1-己烯共聚结果表明，POSS改性催化剂活性较高，最高可达1.03×10⁶ g?（mol?h）^-1，同时具有更高的共聚能力，共聚产物中共聚单体摩尔分数可达3.79%，且聚合产物具有较窄的分子量分布（MWD=3~6）。

关键词: Ziegler-Natta催化剂, 大孔SiO₂, 聚倍半硅氧烷, 乙烯, 1-己烯, 共聚

CLC Number:

TQ 322.2

WANG Ning, HUI Lei, CHEN Mei, LI Wei, ZHOU Qi. POSS-modified supported Ziegler-Natta catalyst and its ethylene /1-hexene copolymerization[J]. CIESC Journal, 2021, 72(4): 2102-2112.

王宁, 惠磊, 陈美, 历伟, 周琦. POSS改性负载型Ziegler-Natta催化剂及其乙烯/1-己烯共聚反应[J]. 化工学报, 2021, 72(4): 2102-2112.

Figures/Tables 13

Fig.1 FTIR spectra of the materials, supports and catalysts

Fig.2 Thermal analysis of the supports

Fig.3 CO low-temperature adsorption DRIFT spectra for catalysts

Fig.4 SEM images[(a),(c)], Ti element EDX[(b),(d)], and TEM images[(e),(f)] of the catalysts before and after modified by POSS

Fig.5 Pore size distribution of the catalysts

Table 1 The structure parameters of catalysts

Run	Cat.	Ti^①/%(mass)	Specific surface area^②/(m³·g^-1)	Pore size/nm
1	Cat-POSS-0	6.9	120	10.2
2	Cat-POSS-10	8.0	135.6	10.4
3	Cat-POSS-20	7.7	135.7	10.8
4	Cat-POSS-30	7.3	83.8	8.2
5	Cat-POSS-50	7.5	50.5	7.2

Fig.6 Kinetics curves of ethylene polymerization

Table 2 The ethylene/1-hexene copolymerization results of different catalysts

Cat.	1-Hexene/ %(vol)	1-Hexene content^①/%(mol)	Activity/ (g·(mol?h)^-1)	PE yield/g	$T m 2$ ^②/℃	$X m 2$ ^②/%	Weight-average molecular weight, $M w$	Molecular weight distribution, MWD
Cat-POSS-0	0	—	2.9×10⁵	3.2	136.4	46.6	172.7×10⁴	7.2
	3	0	3.4×10⁵	4.3	129.2	45.7	134.8×10⁴	8.0
	5	0	3.8×10⁵	4.0	127.5	43.8	129.5×10⁴	6.0
	9	4.3	4.2×10⁵	4.7	125.6	40.5	109.1×10⁴	7.6
	17	8.7	3.1×10⁵	3.5	122.5	34.8	88.7×10⁴	7.3
Cat-POSS-20	0	—	3.3×10⁵	4.5	137.6	48.6	94.8×10⁴	3.8
	3	0.1	7.2×10⁵	9.7	131.7	32.1	91.2×10⁴	4.6
	5	0.7	7.3×10⁵	9.8	130.6	33.1	88.7×10⁴	4.7
	9	3.5	9.9×10⁵	13.3	128.7	32.4	84.3×10⁴	4.8
	17	18.9	10.3×10⁵	13.8	126.2	29.6	74.4×10⁴	6.1

Table 2 The ethylene/1-hexene copolymerization results of different catalysts

Cat.	1-Hexene/ %(vol)	1-Hexene content^①/%(mol)	Activity/ (g·(mol?h)^-1)	PE yield/g	$T m 2$ ^②/℃	$X m 2$ ^②/%	Weight-average molecular weight, $M w$	Molecular weight distribution, MWD
Cat-POSS-0	0	—	2.9×10⁵	3.2	136.4	46.6	172.7×10⁴	7.2
	3	0	3.4×10⁵	4.3	129.2	45.7	134.8×10⁴	8.0
	5	0	3.8×10⁵	4.0	127.5	43.8	129.5×10⁴	6.0
	9	4.3	4.2×10⁵	4.7	125.6	40.5	109.1×10⁴	7.6
	17	8.7	3.1×10⁵	3.5	122.5	34.8	88.7×10⁴	7.3
Cat-POSS-20	0	—	3.3×10⁵	4.5	137.6	48.6	94.8×10⁴	3.8
	3	0.1	7.2×10⁵	9.7	131.7	32.1	91.2×10⁴	4.6
	5	0.7	7.3×10⁵	9.8	130.6	33.1	88.7×10⁴	4.7
	9	3.5	9.9×10⁵	13.3	128.7	32.4	84.3×10⁴	4.8
	17	18.9	10.3×10⁵	13.8	126.2	29.6	74.4×10⁴	6.1

Fig.7 The GPC and WMD of ethylene/1-hexene copolymer

Fig.8 FTIR spectra of polyethylene and ethylene/1-hexene copolymers

Fig.9 The 13C NMR of copolymer

Table 3 Chemical shift of copolymer of ethylene and 1-hexene

No. of peak	Monomer sequence	Chemical shift
No. of peak	Monomer sequence	Theoretical	Experimental
1	EHE	37.78	37.82
2	EHEE	34.54	34.48
3	EHE	34.14	34.26
4	HEEE	30.47	30.28
5	EEE	30.00	29.96
6	EHE	29.34	29.42
7	HHEE	27.09	27.22
8	EHE+HHE+HHH	23.37	23.20
9	EHE+HHE+HHH	14.12	14.02

Fig.10 DSC curves of the obtained polyethylene

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