I don't think the decrease of concentration of coordination catalyst may cause the MW decrease. Since the coordination catalyst usually play more important role in initiation of polymerization, and propagation rate usually faster than initiation. Initiation become the r.d.s. of polymerization. High concentation of catalyst mean more active center in initiation stage, and low molechlar weight of polymer produced. The MW of polymerization usually depend on the the ratio of rate constant for chain propagation with initiation and catalyst concentration.

Thank you Professor Horng for the reply. I wonder if there are some chain transfer agents that can be used to control molecular weight of polymer.

Dear all;

are youi dealing with a metallocene-MAO system. The answer of Dr. Keh Ming Horng not sharp, at the beginning he thinks there is no effect of the concentration and at the end he says there is an effect on the molecular weight, may be he should add an additional clarification for his point of view. Regards

I never say that I think there is no effect of the concentration. Otherwise, high concentation of coordination catalyst  usually means more active center in initiation stage, and low molechlar weight of polymer produced.

By the way,  chain transfer agent is indeed used to control molecular weight and molecular weigfht dispersity of polymer.

Dear all,

Sorry Dr. Keh Ming Horng for my misunderstanding, it is this statement that make meto think so "I don't think the decrease of concentration of coordination catalyst may cause the MW decrease". However, the decrease in the concentration of the catalyst increases the MW weight up to the level where the propagation becomes diffusion controlled, in this situation long chains become more difficult to move favoring the formation of new chains and the enhanced propagation of the medium length chains.

Chain transfer are used to control the MW and the MWD, as it is mentionned in the question for the RAFT process, and in fact this is more than usual in radical polymerization. The author of this question didn't precised the type of COORDINATION POLYMERIZATION? to be more specific in our answers. I have attached some documents with the hope that they will help you somehow in your work. Regards

As in the other types of chain-reaction polymerization, the propagation step in coordination polymerization is the key step & its rate is independent of the rate of the initiation step. However, more concentration of initiator or catalyst (as in coordination polymerization) will cause more chains to grow which will give lower molecular weight. Chemical industries, such as ICI, sent us an advice (while I was a student more than 31 years ago) to lower the initiator/monomer ratio as much as possible to get  high molecular weight polymers.

Thanks all, Especially Mr. Abdelkader for detailed explanation and documents as well as Mr. Horng. Basically, I am going to deal with ROMP of cyclic olefins. Indeed, I want to make low MW polymer or precisely control MW according to requirements and want to keep minimum wt% of catalyst, so that means it is necessary to use some CTA which will help me to get low/desired MW polymer with low percerntage of catalyst.

Dear all;

no thanks, please feel free to ask me for any additional help, maily if you need some specific documents on the ROMP. Regards

I am glad to discuss with all of you. It seems that we are all interesting in coordination polymerization. I have also some experiences on m-COC and ROMP ten years ago. Thank Mr. Abdelkader for your documents, and  good luck to Mr. Mohan N. Wadekar.