Precipitation Copolymerization of Vinyl-Imidazole and Vinyl-Pyrrolidone, 1- Experimental Analysis~a

摘要

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, witha first mode at around 10 (Jim, corresponding to clusters of nucleated primary particles, and a second larger mode at around 100 (xm, corresponding to aggregates of such clusters. The smaller clusters show fractal geometry, with a fractal dimension of ~2.5, corresponding 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.