II. Simulations of polymer growth and isomerization
{"Image DocumentName": "II. Simulations of polymer growth and isomerization", "Image ImageDescription": "The results of our studies on the ethylene and propylene polymerization catalyzed by Brookhart complexes are used as input data for stochastic simulations of polymer growth and isomerization. Based on the assumption that relative probabilities of the events possible in the catalytic cycle are equal to the relative rates of the elementary reactions, these simulations allow one to investigate an effect of the temperature and the olefin pressure on the polymer structure. It is known from experimental studies (Guan Z; et al. Science 1999, 283,2059) that in the case of Brookhart catalyst the change in the olefin pressure does not affect the total number of branches, but strongly influence the microstructure of resulting polymer: from mostly linear polymers obtained for high pressure to hyper-branched structures for low pressure values. In our simulations we build one polymer chain at a time, starting from a olefin insertion into the Pd-methyl group. The structure of the polymer is remembered, and at every step the stochastic choice of the next event is made, on the basis of relative probabilities, calculated from the energetics of elementary reactions. For example, if the primary carbon (a) [Fig4.] is attached to the metal, then the olefin uptake followed by insertion, as well as one isomerization reaction (leading to a secondary carbon being linked to Pd) are possible; if the primary atom (b) is attached to the metal, a choice is made between olefin capture/insertion and an isomerization leading to a secondary carbon; if the secondary carbon (c) is attached to the metal, then a capture/insertion event is possible, or two equivalent isomerization events; from carbon (d), besides a capture/isomerization, two inequivalent isomerisation reaaction are taken into account; etc. In the propylene case, the two insertion paths (1,2- and 2,1-) are considered. Energetics of elementary reactions. Relative probabilities of the. elementary reactions. Choice of a path. relative probabilities = relative rates: e.g. isomerization vs. isomerization: isomerization vs. insertion: etc. Fig.4. 7.", "Image XResolution": "37", "Image YResolution": "37", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}