Precipitation Copolymerization of Vinyl-Imidazole and Vinyl-Pyrrolidone, 1 – Experimental Analysis a Paolo Arosio, Matteo Mosconi, Giuseppe Storti, Massimo Morbidelli* Introduction Copolymers containing vinyl-imidazole (VI) and vinyl- pyrrolidone (VP) are highly functionalized polymers exhibiting attractive combinations of the different proper- ties of the two corresponding homopolymers. [1] Polyvinylpyrrolidone (PVP) is the technically most important polymer belonging to the family of poly-N- vinylamides. This material exhibits interesting properties since it contains both a non-polar substructure and a polar amide group which allow the pyrrolidone unit to favorably interact with hydrophobic as well as hydrogen-bonded and dipolar compounds. [2] On the other hand, the imidazole structure of VI possesses a marked tendency to complex formation both with organic substrates (e.g., proteins, enzymes, and dyes) and with metal ions, such as iron, copper, nickel, and silver. Due to this ability to form Full Paper P. Arosio, M. Mosconi, Dr. G. Storti, Prof. M. Morbidelli Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland Fax: 0041 44 632 10 82; E-mail: morbidelli@chem.ethz.ch a Supporting Information is available from the Wiley Online Library or from the author. The precipitation copolymerization of two water-soluble monomers, vinyl-imidazole and vinyl-pyrrolidone, carried out in butylacetate is investigated for the first time. Compared to classical solution polymerization it is found that much larger molecular weights are obtained. Such large polymer chains are formed by a crosslinking reaction occurring in the precipitated polymer particles. The dependence of the reaction kinetics on operating parameters such as monomer mixture composition (from vinyl-imidazole homopolymer to the 50/50 copolymer), monomer mixture holdup, initiator amount, and stirring rate has been elucidated. Notably, it is found that the polymerization kinetics is independent of the particle size distribution (PSD). Therefore, the polymerization mechanism and the morphology of the precipitating particles can be investigated separately. The final PSD is broad and bimodal, with a first mode at around 10 mm, corresponding to clus- ters of nucleated primary particles, and a second larger mode at around 100 mm, corresponding to aggregates of such clusters. The smaller clusters show fractal geometry, with a fractal dimension of 2.5, corre- sponding to quite compact aggregates. The size of the two peaks, the ratio between the two modes and the time evolution of the PSD are all depending on the aggregation/breakage processes in the reactor, which are affected by operational parameters like the copolymer composition and the shear rate. 0 0.5 1 1.5 2 2.5 3 0 10 20 30 40 50 60 70 80 90 100 t/tc Conversion (%) VP content 0 0.5 1 1.5 2 2.5 3 0 10 20 30 40 50 60 70 80 90 100 t/tc Conversion (%) VP content 490 Macromol. React. Eng. 2011, 5, 490–500 ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com DOI: 10.1002/mren.201100019