Research > Projects
Detailed study of free-radical polymerization steps

Propagation and termination rate coefficients for homo- and copolymerization reactions in wide ranges of temperature, pressure and monomer conversion are being determined using laser-assisted techniques. The resulting rate coefficients are used to simulate conversion vs. time curves in polymerization reactions and to assess the relationship between reaction conditions and the properties of the polymeric product. Measured rate coefficients also serve for checking and generalizing copolymerization models. The description of diffusion control of the termination step is being studied in detail, especially the dependence of termination kinetics on radical chain length and on the molecular weight of polymer produced during preceding polymerization.
Detailed kinetic investigations into radical polymerizations of water-soluble monomers in aqueous phase

Rate coefficients of propagation and termination for aqueous acrylic acid polymerizations are determined. To initiate the reactions, pulsed laser techniques are applied. The dependence of rate coefficients on monomer concentration, on pH, and on the degree of ionization is investigated. FT-IR and FT-Raman spectroscopy are used to study speciation. The studies are extended to methacrylic acid and to several other water-soluble monomers.
Project leader:
Prof. Dr. Michael Buback,
Dr. Igor Lacík

Team:
Nils Wittenberg

Start: 1.6.2000

Contributing institution:
Polymer Institute of the Slovak Academy of Science, Bratislava
High-pressure ethene (co)polymerization with polar comonomers

Polyethylene homopolymer and ethylene-based copolymers, mostly with (meth)acrylates being the comonomers, are produced under reaction conditions up to 3000 bar and 300°C using a high-pressure mini plant device. Composition data are used to determine reactivity ratios over a wide range of reaction conditions. Rate coefficients for transfer reactions are derived from the polymeric microstructure.
Kinetics of Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization

This research project concentrates on investigations into the kinetics and mechanism of the RAFT process, which is not yet completely understood. Knowledge about the mechanism is essential for optimizing the process and for applying the RAFT polymerization to an extended field of monomers and polymerization conditions. Influences of high pressure up to 3000 bar and of supercritical CO2 on both the molecular weight control and the polymerization rates are studied in detail. The experimental work is accompanied by electron spin resonance (ESR) spectroscopy of the radical intermediate species and by modeling of the RAFT polymerizations using both PREDICI and novel Monte-Carlo methods, in order to derive kinetic parameters describing the complex RAFT equilibrium.
Project leader:
Prof. Dr. Philipp Vana,
Prof. Dr. Michael Buback

Team:
Dr. Tatiana Sergeeva,
Dipl.-Chem. Olaf Janßen

Start: 1.10.2003
Investigations into the initiation process of radical polymerizations via Electrospray Ionization Mass Spectrometry (ESI-MS)

Based on studies into cage reactions after initiator decomposition, the fate of the produced radicals in the time period between cage exit and addition to a monomer molecule ("initiation step") is studied. The radicals may undergo fragmentation, transfer reactions or rearrangement prior to the actual initiation process, generating a variety of radical species that are incorporated as end-groups of the polymeric material. Knowledge about these end-groups is important for material properties, especially in cases where low molecular weight material is produced, as well as for gaining detailed insight into the kinetics of the initiation process. Electrospray Ionization Mass Spectrometry is an excellent tool for studies into the type of polymeric end groups.
Project leader:
Prof. Dr. Michael Buback,
Prof. Dr. Philipp Vana

Team:
Dipl.-Chem. Felix Huff,
Dipl.-Chem. Olaf Janßen

Start: 1.10.2004

Contributing institution:
Chemical analysis department of the Institute of Organic Chemistry, University of Göttingen, Dr. Holm Frauendorf
Determination of the phase behavior of ethylene-based copolymers

Knowledge about the behavior of the phase boundaries in monomer – polymer systems during and after polymerization is mandatory. The occurrence of two phases influences both the properties of the polymeric product and the safe handling of the reaction. Information on the phase boundary is also necessary for optimizing the separation of the product mixture. For high- pressure ethene copolymerizations, cloud point pressures are measured over wide ranges of temperature and of the compositions of both monomer feed and copolymer. The experiments are carried out either in a batch reactor or under continuous operating conditions in an optical cell, that is mounted downstream of the continuously stirred polymerization reactor. In cooperation with the group of Prof. Sadowski (University Dortmund) the results are modeled by the PC-SAFT method.
Project leader:
Prof. Dr. Michael Buback

Team:
Dipl.-Chem. Florian Becker

Start: 1.1.1999
Modeling of the kinetics and of the product properties of radical polymerization processes

The conversion vs. time dependencies and the properties of high molecular weight products are described on the basis of a comprehensive kinetic model for high-pressure homo- and co- polymerizations. The simulations are performed via the commercial software package PREDICI. The activity aims at the simulation and optimization of technical polymerization reactions.
Project leader:
Prof. Dr. Michael Buback

Team:
Dipl.-Chem. Florian Becker, Andreas Redeker

Start: 1.1.1999
Decomposition kinetics and initiator efficiency of peroxides in free-radical polymerizations

The decomposition of organic peroxides in dilute solutions is studied by quantitative in-line IR spectroscopy within a wide pressure and temperature range. The experiments are carried out under both discontinuous and continuous operation conditions. The studies aim at both the accurate determination of initiator decomposition rate coefficients which are required for modeling free-radical polymerization and at the elucidation of decomposition mechanisms which allow for deducing information on initiator efficiency. For ethene high-pressure polymerization such efficiencies are measured in a miniplant device equipped with continuously stirred tank reactor.
Synthesis of estrone in supercritical fluid phase

A novel type of supercritical fluid-phase reaction is studied in which estrone is produced in a continuous tubular reactor process from the starting material 1,4-androstadiene-3,17-dione. Favorable selectivity and yield are reached on a sub-second time scale at temperatures around 550 °C and at pressures around 100 bar. Shock heating is performed with very hot scCO2.
Project leader:
Prof. Dr. Michael Buback

Team:
Dipl. Chem. Duc Hung Nguyen,  Chunqiao Wang, Dr. Hans-Peter Vögele

Start: 1.1.2001
Femtosecond time-resolved measurements of the dissociation dynamics of peroxy compounds

The unimolecular decomposition of aromatic peroxy compounds is studied by UV-VIS- and UV-IR-pump-probe techniques with a time resolution of pico- or femtoseconds. In addition to the time dependence of the concentration of transient species and product molecules, the dynamics of cooling of intermediates has been observed as well. The decomposition kinetics are modeled by statistical theories based on data from quantum- chemical calculations.
Project leader:
Prof. Dr. Michael Buback, Prof. Dr. Jörg Schroeder, Prof. Dr. Bernd Abel, PD Dr. Stefan Schmatz,

Team:
Dr. Matthias Kling

Start: 1.1.1999
End: 31.12.2004

last edited: Sept. 21, 2006