To gain insights into the microstructure of polyvinylpyrrolidone (PVP), a detailed reaction mechanism is developed, which characterizes the polymer along the property coordinate chain length, terminal double bonds (TDB), and branching points. For practical purposes, calculations with three property coordinates are unfeasible, and model reduction is needed. Here, a reduced model with only one single property coordinate without significant loss of accuracy is derived. In the first step, the coordinate TDBs are reduced by a linear relationship between TDBs and chain length. As the parameters of this relation are state dependent, they are dynamically adjusted from a parallel calculated 0D model. In a second step, the pseudodistribution approach is used to reduce the 2D distribution to chain length as the only property coordinate and calculate moments of branching points as a function of chain length. A 2D class model is set up for validation. To demonstrate the benefits of the model, the chain length distribution and moments of branching points are calculated for different average residence times and monomer concentrations in a stirred tank reactor. In a future publication, the model will be validated by experimental data in terms of chain length distribution and branching points.

Deposit formation and fouling in reactors for polymer production and processing especially in microreactors is a well-known phenomenon. Despite the flow and pressure loss optimized static mixers, fouling occurs on the surfaces of the mixer elements. To improve the performance of such parts even further, stainless steel substrates are coated with ultra-thin films which have low surface energy, good adhesion, and high durability. Perfluorinated organosilane (FOTS) films deposited via chemical vapor deposition (CVD) are compared with FOTS containing zirconium oxide sol-gel films regarding the prevention of deposit formation and fouling during polymerization processes in microreactors. Both film structures led to anti-adhesive properties of microreactor component surfaces during aqueous poly(vinylpyrrolidone) (PVP) synthesis. To determine the morphology and surface chemistry of the coatings, different characterization methods such as X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy as well as microscopic methods such as field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) are applied. The surface free energy and wetting properties are analyzed by means of contact angle measurements. The application of thin film-coated mixing elements in a microreactor demonstrates a significant lowering in pressure increase caused by a reduced deposit formation.

A polymer distribution is usually represented by its moments. Thus, to calculate transport in a polymer system, a formulation for the transport of moments of the polymer is needed. This is only possible if the moments close or if there is a suitable closing condition. To archive this, two simplifications of the Stefan–Maxwell diffusion are derived, which convert the transport equation of polymeric species to a closed set of transport equations for the polymer moments. The first approach corresponds to an infinitely diluted polymer system, whereas the second one describes a highly concentrated polymer system. Both formulations are compared with the full Stefan‐Maxwell model of a ternary mixture of a solvent and two polymer species of different chain length.

No abstract

To predict the polymer properties produced by free‐radical polymerization of N‐vinylpyrrolidone (NVP) in aqueous solution a detailed kinetic model has been developed. The kinetic model allows to calculate the chain length distribution, the number of branching points, and the number of terminal double bonds (TDB). The latter is accounted for since TDBs are a precondition for branching. While monomer conversion can be predicted sufficiently using independently determined rate constants for propagation and termination, here the predictions of structural properties by a newly developed extended kinetic model to experimental findings are compared. Polymer produced in a continuous stirred tank reactor is analyzed by gel permeation chromatography (GPC), field flow fractionation (FFF), and high‐pressure liquid chromatography (HPLC).