we specialise in cold polymerization of styrene and butadiene, and we are loosing butadine during polymerization in dimerization to (4 -vinylcyclohexene) about 8% is found during GC analysis
i would like to know the conditions/or catalyst that initiate and promote dimerization of 1.3-butadine to 4 -vinylcyclohexene
Dear Rendani, this is probably due to Diels-Alder Reaction. Diels Alder reaction needs no catalyst but SiC and Cu salts may catalyze the reaction. Temperatures are as low as 110oC.
if your familiar with cold SBR Emulsion polymerization formulation you will know that we dont have Sic and Cu salts# instead we have Ferrous salt, would this catalyze the dimerization and if we would like to reduce this dimerization what actions should we take?
Dear Rendani, I worked on Bd/Ba emulsion polymerization in the past, and I observed the presence of the Diels Alder adduct in my system as well.
I am afraid, and if my memory is correct, that in order to minimize the ammount of DA adduct you have to increase temperature. You may want to check this even if it is clearly not in line with you objectives.
we are limited to run our reaction to max of (9.5 degree celc).., this is to avoid cis-structures in our polymer chains for quality purposes
but i should come to think that if we increase the temperature, the dimerization will be favoured. since the high the temperature the greater chance of forming cis-butadienes structures which promote the dimerization
Dear Rendani, in fact diene dimerizations are favoured when you increase temperature, this is a thermodynamic fact and you can estimate the degree of reacted butadiene by estimating the equilibrium constant. I have observed these dimerizations under three circumstances: 1) Under acidic conditions, but as I remember in emulsion polymerization at low temperatures the pH is not acidic on the contrary it is usually above 7.0, but the tensoactive and salts determine the pH value, verify pH. 2) The other circumstance might be a very important amount of butadiene in the gas phase, at 9 °C you might have around 35 % of your butadiene in the gas phase and the rest in the emulsion bulk. Try first estimating the amount of butadiene in the gs phase. This free butadiene is not in contact with your redox system and it is free to dimerize, instead of being polymerized, "in thermodynamic equilibrium". The answer is to increase pressure in your reactor adding an inert gas (nitrogen) or increasing its pressure. I suppose you have a reactor that can stand moderate pressures, try to reduce the amount of butadiene in the gas phase increasing the overall pressure with nitrogen. 3) The last circumstance that might be the cause of dimers is the presence of oxygen inside your reactor. As you know redox systems are very easy to deactivate when oxygen is present. The answer might be bubbling nitrogen in to water previously to the addition of the monomers. Moreover, if you follow the previous advice, increaing pressure with nitrogen, you might reduce both problems oxygen presence and free butadiene in the vapor phase. If these solutions are not enough let us know. Good Luck!
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