Scientific publications

Poly(propylene-co-ethylene) Produced with a Conventional and a Self-Supported Ziegler–Natta Catalyst: Effect of Ethylene and Hydrogen Concentration on Activity and Polymer Structure

2012, Torvald Vestberg, Matthew Parkinson, Isa Fonseca, Carl-Eric Wilen.

Poly(propylene-co-ethylene) Produced with a Conventional and a Self-Supported Ziegler–Natta Catalyst: Effect of Ethylene and Hydrogen Concentration on Activity and Polymer Structure
Journal of Applied Polymer Science, 124 (-), 2012, 4889-4896

A novel self-supported emulsion-based catalyst and a conventional MgCl2-supported Ziegler–Natta catalyst were used in the copolymerization of propylene and ethylene under industrial conditions using triethyl aluminium as cocatalyst and dicyclopentyl dimethoxy silane as external donor. The effects of the concentration of ethylene and hydrogen on the polymerization behaviors and polymer properties were investigated. The combined effect of both ethylene and hydrogen increased the relative activity of the novel catalyst more than for the conventional catalyst. This trend was consistent with our earlier observed higher degree of dormancy, due to 2,1 insertions, found with the novel catalyst. More importantly, the work has uncovered that the self-supported catalyst incorporates ethylene in a more random fashion and produces copolymers with relatively narrow molecular weight distribution (MWD). These results in combination with polymer microstructure studies using Fourier transform infrared spectroscopy, 13C-NMR spectroscopy, and differential scanning calorimetry all indicated that the novel catalyst has a narrower distribution of active site types than the conventional reference catalyst. The narrow composition of active site structures, the narrow MWD, and the random incorporation of ethylene into the polymer chain indicated that the emulsion-based catalyst possesses features that to a certain degree tend to be more indicative for a single-sitelike catalyst structure and behavior.

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Thin Film Structure of Block Copolymer−Surfactant Complexes: Strongly Ionic Bonding Polymer Systems

2012, Jingbo Wang, Wim H. de Jeu, Paul Müller, Martin Möller, Ahmed Mourran.

Thin Film Structure of Block Copolymer−Surfactant Complexes: Strongly Ionic Bonding Polymer Systems
Macromolecules, 45 (-), 2012, 974−985

We present a structural investigation of thin films of diblock copolymers PS−P4VP in which 4VP forms an ionic bond with a sterically demanding surfactant, bis (2-ethylhexyl) sulfosuccinate acid (AOT). The results depend strongly on the interplay between microphase separation and surfactant ordering. Protonation of the P4VP homopolymer or diblock PS-b-P4VP with AOT leads to a multilayer structure in which the surfactant determines the layer thickness. In thin films of the protonated block copolymer, the segregation between the blocks generates nanostructures with an inplane periodicity defined by the molecular masse of the copolymer and the stoichiometry of the complex. Variation of the composition of the blocks and the molar ratio AOT/pyridine leads to structural transitions: cylinders of (AOT/P4VP) → lamellae → cylinders of PS. Remarkably, regardless of the morphology, the bcp microdomain structure remains orthogonal to the air substrate interface. Finally, we show that hydrolysis of AOT results in the formation of pores with a variable geometry useful for templating two-dimensional inorganic structures.

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Structure-Property Relationships in Biaxially Oriented Polypropylene Processing

2012, Dietrich Gloger, Martina Sandholzer, Gottfried Kandioller.

Structure-Property Relationships in Biaxially Oriented Polypropylene Processing
POLYCHAR 20 World Forum on Advanced Materials, 26-30 March 2012 Dubrovnik, HR, - (-), 2012, -

Biaxially oriented polypropylene (BOPP) is an important material and is used as packaging film and for certain speciality applications. The biaxial orientation process to generate a BOPP film from isotactic polypropylene (iPP) is a three-stage process. The first stage concerns the casting of an initial film, in the second stage this cast film is then subsequently drawn in the direction of casting, the so-called machine direction (MD), creating a machine direction orientated (MDO) film. In the final stage the MDO film is stretched in the transverse direction (TD) creating the final thin BOPP film. Such BOPP films are characterised by a fibroid crystalline morphology created from the original spherulitic morphology present in the cast film. As the biaxial orientation process is demanding, a specific rheological and thermal behaviour of the polymer is required. The response of the polymer to such conversion defines the properties of final BOPP film and hence its performance in the final application. To better control end use properties, an indepth understanding of the link between polymer and final properties is desired. iPPs produced using Borealis’ proprietary Borstar® process were subjected to pilot scale BOPP stretching experiments. The processing conditions in terms of temperature settings of the cast film extrusion and the transversal stretching temperature were varied according to Design of Experiments (DoE) principles. Samples of the cast film, the MDO film and the final BOPP film produced with different thermal history were collected and studied. The morphology was characterised by wide-angle x-ray scattering (WAXS), tensile testing and density measurements. This enabled the study of changes in morphology along the conversion process. Structure property processing relationships could be established.

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Nouvel Non-Linear Rheological Parameters for Polyolefin Quality Control

2012, Anh Tuan Tran, Susana Filipe, Katja Klimke.

Nouvel Non-Linear Rheological Parameters for Polyolefin Quality Control
SPE ANTEC Conference 2012 April 2 – 4th, Orlando – Florida, USA, - (-), 2012, -

The continuous demand of high performance materials with key properties requires the optimization of polymerization and post-reactor treatment processes. A multiscale characterization approach including techniques such as rheology, fractionation and NMR has proven to be essential to understand the links between polymerization conditions, molecular structural properties and end performance. Rheology is a preferred candidate for analytical characterization, since its use provides combined knowledge on molecular characteristics and processability. A key parameter for the performance of materials during processing is the so-called LCB. Rheology, in particular methods exploring the longest relaxation mechanisms, is known to provide a significant insight into the type and amount of longer chains incorporated during polymerization. Most of the existing rheological parameters used by Industry and Academia, to correlate molecular structure and processability, are based on techniques that are often time consuming and which, for most of the cases, are only applicable to a given class of materials. The increasing need to reduce “time to market” requires the development of more sophisticated and efficient characterization tools. The combination of different non-linear viscoelastic methods presented within this work will provide further insight into the links between molecular structural properties and polymerization conditions. The use of the Large Amplitude Oscillatory Shear (LAOS) together with uniaxial extensional flow measurements can bring new understanding on the nature of the non-linear viscoelastic response of LCB materials and its correlation with molecular characteristics.

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Formation of Self-Assembled Organosilicon-Functionalized Quinquethiophene Monolayers by Fast Processing Techniques

2012, Elena V. Agina, Ivan A. Usov, Oleg V. Bourshchev, Jingbo Wang, Ahmed Mourran, Maxim A. Shcherbina, Artem V. Bakirov, Souren Grigorian, Martin Moeller, Sergei N. Chvalun, Sergei A. Ponomarenko.

Formation of Self-Assembled Organosilicon-Functionalized Quinquethiophene Monolayers by Fast Processing Techniques
Langmuir, 28 (-), 2012, 16186-16195

Different techniques for a relatively fast self-assembled monolayer film formation such as Langmuir−Blodgett (LB), spincoating, and dip-coating methods have been compared using chloro[11-(5′′′′-ethyl-2,2′:5′,2″:5‴,2‴:5‴,2′′′′-quinquethiophene-5-yl)undecyl]dimethylsilane as a reactive precursor. It was shown that both spin-coating and LB techniques are very promising methods for preparation of highly ordered monolayer films of organosiliconfunctionalized quinquethiophene with vertical orientation of oligothiophene fragments, while dip-coating gives only partial coverage. Optimal conditions for complete filling out the substrate surface by the quinquethiophene-containing monolayer by spin-coating and LB methods have been found. Grazing incidence X-ray diffraction measurements confirmed formation of in-plane crystalline order within the monolayer film. Changes in the layer structure were established by X-ray reflectivity and grazing incidence X-ray diffraction methods.

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