Morphology Evolution in the Early Stages of Olefin Polymerization

Abstract

Summary:The olefin polymerizations were carried out by using silica supported metallocene/MAO catalysts and MgCl 2 supported Ziegler-Natta catalysts under mild reaction conditions and stopped at very low yield. The surface and cross sectional morphology of the polymer particles were characterized by using scanning electron microscopy (SEM). A homogeneous distribution of (co)catalyst on the support material is a prerequisite condition to get a homogeneous fragmentation and uniform polymer particle morphology. In the present work the catalysts show two different fragmentation behaviors. They can gradually fragment from the outer to the inner surface of the catalyst particle, or instantaneously break up into a large amount of small sub-particles at the beginning of the polymerization. The incorporation of comonomer does not change the general catalyst fragmentation scheme but delays the catalysts break-up progress.

Ethylene/1‐Hexene Copolymers Produced with MAO/(nBuCp)2ZrCl2 Supported on SBA‐15 Materials with Different Pore Sizes

“…[44,45] It is also possible that the copolymer made at higher comonomer concentrations could be too ''soft'' to break the support particles effectively, failing to expose the less accessible active sites and reducing the apparent catalytic activity. [46] Figure 5 demonstrates that the carrier pore size has a strong influence on the ethylene polymerization kinetics. In homopolymerization (Figure 5a), the catalyst made with the SBA-15 support with the largest pore size shows a buildup polymerization rate curve with no apparent catalyst deactivation, while the support with the smallest pore size, which could imply a greater steric hindrance, had a decay type profile, with initial high catalytic activity followed by a steadily polymerization rate decrease.…”

Uma revisão sobre polimerização de olefinas usando catalisadores Ziegler-Natta heterogêneos

“…O grau de resistência (relacionada às características mecânicas do suporte) às forças exercidas pelas moléculas de polímero em crescimento e a acessibilidade dos sítios ativos (relacionada ao volume de poro, à área específica e à distribuição de tamanho dos poros) são fatores críticos para processo de ruptura. [54] Além disso, cada estrutura de suporte catalítico requer uma análise particular em termos de seus parâmetros físicos e de suas propriedades estruturais [55,56] . A forma exata dos fragmentos da estrutura original do catalisador geralmente pode ser determinada por fatores tais como as propriedades físicas do suporte catalítico, a atividade do catalisador e as fases presentes no reator [30] .…”

Polymerization on Molecular Catalysts

“…Since many industrial catalysts are in fact prepolymerized under milder conditions in a separate reactor before being fed to the polymerization reactor, this should not be seen as limitation of the [213,214] covers these questions and some alternative models. According to Loos and coworkers [30,[217][218][219], these investigations show that there are basically two different ways by which the catalyst particles can break up in the case of MgCl 2 -supported Ziegler-Natta catalysts as in the case of silica-supported metallocene/MAO catalysts. 0.8-1.4 g polymer g −1 cat ), respectively [30,200,215,216].…”

“…According to Loos and coworkers [30,[217][218][219], these investigations show that there are basically two different ways by which the catalyst particles can break up in the case of MgCl 2 -supported Ziegler-Natta catalysts as in the case of silica-supported metallocene/MAO catalysts. Several parameters influence the fragmentation during the early stages of polymerization: the physical properties and the active site distribution, the polymerization rate (related to the catalyst activity and the polymerization conditions applied, such as monomer pressure and reaction temperature) and mass and heat transport (related to reactor design, the porosity of the particles and the crystallinity of the polymer formed) [217,219]. As an example, Fig.…”