Question

The ROMP reaction with 1,5-COD forms long polymers that precipitate in dichloromethane after 30 minutes. However, if reaction is left running for a few hours, no precipitate will form when methanol is added. Explain why. (Worth noting that oligomers are soluable and will not precipitate in CH2CL2)

Answer 1

Answer: The ring opening metathesis polymerization with 1,5-cyclooctadiene results in the formation of high molecular weight long chain polymers. The procedure involves heating of 1,5-COD in dichloromethane in presence of catalyst (There are many catalyst used for ROMP eg Grubbs catalyst). After completion of reaction methanol is added which leads to the formation of precipitate of polymer followed by its filtration. If the reaction is carried out for longer time, it results in the degradation of initially synthesized polymer due via chain scission which results in the formation of low molecular weight polymer (oligomers). Low molecular weight polymers are soluble in methano-dichloroform mixture and therefore they did not form precipitate.(In these cases for separation, solvent was simply evaporated after the polymerization was complete, and residual catalyst was removed using silica gel chromatography.)

ROMP Chain Scission Oligomers 1,5-COD