Catalyst Type Effects on Structure/Property Relations of Polypropylene Random Copolymers

Abstract

Polypropylene (PP) random copolymers are an important class of commercial materials that can be tuned for a wide range of different applications. The structure-property relations are mainly discussed in this article focusing on two major influencing factors, the catalyst system and the type and amount of comonomer. Ziegler-Natta (ZN) catalyst systems still dominate the production of polypropylene and todays sixth-generation ZN catalysts are based on postphthalate donor systems. Metallocene (MC) catalysts offer possibilities to exactly control the microstructure of the polymer even better. Mostly, ethylene is used as comonomer being randomly distributed for up to 7.3 mol% when using ZN catalysts. For single site catalysts, homogenous (single phase) materials can be achieved up to ethylene contents of 20.8 mol%. The incorporated comonomer reduces the crystallization speed and the lamellar thickness of the polymer thus affording soft and highly transparent materials. Random copolymers and terpolymers with higher 𝜶-olefins only play a minor role but offer an additional possibility for property adjustments. PP random copolymers can also be varied in their performance through multistage polymerizations, altering the comonomer content and or the molecular weight in the different polymerization reactors.

Assessing the Downstream Contamination of Chemically Recycled Ethylene Feed Streams on the Kinetic Behavior of Ziegler‐Natta Catalysts and Microstructural Properties of HDPE and LLDPE

“…[ 19 ] Ziegler‐Natta catalysts (most commonly fourth generation) consist of a solid metal‐halide TiCl 4 species on MgCl 2 ‐support. [ 20,21 ] Upon activation with an aluminum alkyl (most commonly triethylaluminum, TEA), the active catalyst species are formed, characterized by coordinatively unsaturated Ti‐complex sites. It is agreed that four to six different site types are present in a Ziegler‐Natta catalyst, hence their common classification of multisite catalysts.…”

Polymerization in the Borstar Polypropylene Hybrid Process: Combining Technology and Catalyst for Optimized Product Performance

“…One of the main advantages of using the combination of a liquid bulk loop reactor and a fluidized gas-phase reactor (GPR) in series for producing homopolymers and random copolymers with C2 or higher α-olefins like 1-butene (C4) or 1-hexene (C6) is the higher difference in average molecular weight and comonomer content values that can be achieved between the two fractions [ 77 , 78 ]. The use of bi- or multimodality for broadening the MWD with the target of increasing flow-induced crystallization and stiffness [ 79 ] is based on the role of longer molecules in the formation of the stable nuclei and shish-kebab structures mostly studied in solution or extruder blends [ 80 ] and found to increase modulus significantly [ 81 ].…”

“…Bimodal homopolymers with a significant MFR difference between the loop reactor and GPR were among the first innovative products from the Borstar ® PP process (the importance of excellent homogenization for utilizing the enhanced rheological performance has just been highlighted recently again [ 78 ]). Combining increased polydispersity with high isotacticity and selective nucleation gave advantages not only in stiffness, but also in properties otherwise requiring massive orientation in processing like the water vapour impermeability of films [ 73 ].…”

“…Shortly afterward, this design principle was also applied to produce advanced random copolymers [ 83 , 84 , 85 ] in the loop/GPR design. PP homopolymers and C2C3 random copolymers are generally miscible, as long as the comonomer content does not exceed ~8 wt.% for most ZN catalyst types, and as long as the molecular weight difference between the two components is not too high [ 78 , 86 ], resulting in a single-phase structure allowing high transparency and low haze.…”

Thermomechanical Degradation of Polypropylene – Polystyrene Blends During Extrusion‐Based Melt Blending – A First Survey of Shear‐Induced Molecular Architecture Changes

“…[1] PP is a very important commodity plastic and concurrently, it contributes substantially to polymer waste streams. PP is complex concerning to its molecular architecture, in terms of molecular weight and chain irregularity distribution, leading to a broad structure-property spectrum, [4][5][6][7] which can be extended by blending PP with PS, which is further dependent on the specific compatibilization strategy applied. [1,8] Especially, in the field of additive manufacturing, i.e., in filament production for fused deposition modeling (FDM), PP/PS blends improve the flexibility of the filaments and allow tailoring processing properties.…”