File:Polynbornene.svgROMP reaction giving polynorbornene. Like most commercial alkene metathesis processes, this reaction does not employ a well-defined molecular catalyst.
Heterogeneous catalysis consists of catalysts and substrates in different physical states. The catalyst is typically in solid phase.[6] The mechanism of heterogeneous ring-opening metathesis polymerization is still under investigation.[7]
Ring-opening metathesis polymerization of cyclic olefins has been commercialized since the 1970s.[4] Examples of polymers produced on an industrial level through ROMP catalysis are Vestenamer, Norsorex and ZEONEX, among others.[8]
The mechanism of homogeneous ring-opening metathesis polymerization is well-studied. It is similar to any olefin metathesis reaction. Initiation occurs by forming an open coordination site on the catalyst. Propagation happens via a metallacycle intermediate formed after a 2+2 cycloaddition. When using a G3 catalyst, 2+2 cycloaddition is the rate determining step.[9]
Frontal ring-opening metathesis polymerization (FROMP) is a variation of ROMP. It is a polymerization system that reacts via a cascading reaction front after application of a trigger to kick off the reaction in a localized zone.[10] One example of this system is the FROMP of dicyclopentadiene with a Grubbs' catalyst initiated by heat.[11]
