Metallocene Supported on Porous and Nonporous Polyurethane Particles for Ethylene Polymerization
Metallocene Supported on Porous and Nonporous Polyurethane Particles for Ethylene Polymerization
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DOI：
10.1002/pola.27026
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发表时间：
2014-02-15
影响因子：
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通讯作者：
Muellen, Klaus
中科院分区：
文献类型：
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作者：
Dorresteijn, Robert;Nietzel, Sven;Muellen, Klaus
引言聚烯烃与三烷基铝氧烷的组合开辟了生产具有定制性能的聚烯烃的新时代。与齐格勒-纳塔体系相比，茂金属催化的新奇在于活性物质的单中心特征，其产生具有窄的单峰弗洛里粒度分布的聚合物。通过调整聚烯烃的配体，可以通过控制立构规整度和引入离散比例的共聚单体来生产具有特定性能的聚烯烃。3、4尽管有这些优异的性能，但是，它们在工业应用中在均相条件下在低于熔点的聚合温度下的使用遇到一些问题，例如产物的低堆积密度、非常大量的甲基铝氧烷（MAO）作为助催化剂、缺乏形态控制和反应器结垢。由均相烯烃聚合经由异烯烃生产的聚合物仅以不适合于工业应用的粉尘或团块形式获得。为了获得更好的加工性能，需要一种可流动的粉末，这种粉末只能通过将金属茂负载在固体载体上来生产。这种非均相方法提供了更好的形态控制和获得的颗粒的更高的堆积密度，防止反应器结垢。载体材料的适当选择是一个重要因素：6-11（i）载体材料应该由微米级球形颗粒组成，以避免粉尘形成，并具有高表面积、明确的孔径和均匀的粒度分布;（ii）在整个聚合过程中，载体材料应可破碎成纳米尺寸的颗粒，以获得高密度的产物并避免最终产物中的光散射;以及（iii）载体的活性位点应是均相的。
INTRODUCTION The combination of metallocenes with trialkylaluminoxane has opened a new era of producing polyolefins with tailor-made properties. 1, 2 The novelty of metallocene catalysis, in contrast to Ziegler–Natta systems, is the single-site character of the active species which generates polymers with narrow, monomodal Flory-size distributions. By tailoring the ligands of the metallocenes, polyolefins with specific properties can be produced through the control of tacticity and the incorporation of discrete ratios of comonomers. 3, 4 Despite these outstanding properties, however, their use in industrial applications under homogeneous conditions at polymerization temperature below the melt point encounters some problems such as low bulk density of the product, a very large amount of methylaluminoxane (MAO) as co-catalyst, lack of morphology control, and reactor-fouling. The polymers produced from homogeneous olefin polymerization via metallocenes are obtained only in dust or lump form which is not suitable for industrial applications. For better processability, a flowable powder is required which can only be produced by supporting metallocenes on solid carriers. 5 Such a heterogeneous approach provides better morphology control and higher bulk densities of the obtained particles, prevents reactor-fouling. Additionally, the use of a supporting material is the only way to run metallocene polymerizations without a solvent in a gas phase reactor.The proper choice of supporting materials is an important factor: 6–11 (i) The supporting material should consist of micrometer-sized spherical particles to avoid dust formation and possess a high surface area, well-defined pore diameters, and uniform size distributions;(ii) the supporting material should be fragmentable into nanometer-sized particles throughout the polymerization process to achieve a high density product and to avoid light scattering in the final product; and (iii) the active sites of the supports should be homogene-