 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. We have been discussing about olefin polymerization and in particular we have covered ethylene polymerization and propylene polymerization in the last few lectures. With regard to both of these ethylene polymerization as well as propylene polymerization we have come a long way. Let me just briefly summarize as to what has been discussed so far. Where do you proceed from here? What we have seen is with respect to ethylene, we have made polyethylene of various types and for these there have been two types of catalyst mainly this is the famous Ziegler-Natter catalyst and these are mainly a multisite heterogeneous catalyst and we have also seen a metallocene catalyst and they are of the formula MAO, they are of the formula M equals group 4 transition metal as well as X can be halide alkyl alkyl and so on so forth and these are called metallocene catalyst they are homogeneous in nature and they provide narrow PDI polymer whereas the heterogeneous provide broad PDI polymer and these are single site catalyst. The system evolved from one to other, so these are the two types of catalysts one can heterogeneous Ziegler-Natter, metallocene, broad PDI, narrow PDI, high activity, low activity, so these are the two types of the catalyst trajectory that we have discussed. Using these two catalysts we had done elaborate study on polyethylene polymerization using this we have also looked at these are polypropylene it can be isotactic, atactic or syndiotactic depending on the distribution and we had seen how the catalyst evolved for both of these type of catalysts and each of these both the Ziegler-Natter type as well as the metallocene types were equally capable of carrying out this kind of polyethylene polymerization in a very nice way and broad way. We had also discussed another interesting example which is and the catalyst is a metallocene catalyst 8 of 5, so we had also seen this phenyl-indenyl zirconium dichloride with NaO that giving atactic isotactic stereoblocks, isotactic stereobodog polymer polypropylene, so what we saw a nice application of various types of polymer being produced on demand and at will using some variation of these two type of catalyst one is heterogeneous and homogeneous where one can produce not only polyethylene of various grades not only similarly polypropylene of various grades one can also have a stereoblock polymer of different tacticity attached on the same polymer chain using these catalysis, so this is a nice demonstration of the scope and capability of organometallic chemistry that can be put in use, so fantastic demonstration that champions the field of organometallic chemistry for utility in achieving very different difficult or challenging reactions, so today having covered all of these today we are going to take a look at two more types of polymerization particularly the ones that I talk about, so we have talked about three types of polymerization process one, two, three, the fourth one that we would talk about is polymerization between olefin and alpha olefin resulting in polyethylene co-alpha olefin polymer, so this is a polymer that is obtained from co-polymerization of two different monomers, this is one another one and the polymer would have now two fragments one is the polyethylene as well as the polyolefin fragments and the fifth one that we would talk about is a co-polymerization of olefin with functional monomers, so in that case again one may have ethylene plus another polyolefin with functional group, functional group means oxygen, nitrogen, sulphur or heteroatom containing functional mode groups brings polyethylene co-polymer functional group polymer, so here too there are two monomers, one is this functional group bearing olefin co-polymerizing giving polyolefin and monomer inserted functional group polymer, so the emphasis then became important for developing such types of polymer, now one reason for such development is that the surface properties becomes different when one goes for co-polymerization, for example for the fifth process since the functional group is present, so the co-polymer backbone would have a functional group and functional groups are usually a polar in nature, so that will render hydrophilicity to the polymer, so any polymer with hydrophilic application for those purpose this functionalization co-polymerization with olefins and alpha olefins bearing functional groups are important, because all of these polymers as one says they are all hydrophobic in nature, whereas if one can make a polymer with surface functionalized functional group then those polymers would instead be hydrophilic in nature, so these are the reasons where which lead to the need for being able to co-polymerize olefins with alpha olefins as well as ethylene with monomer bearing functional group, just to illustrate my point about the hydrophilicity for example all of these from here all the way up to here they are hydrophobic, whereas this last one will be hydrophilic because of the presence of the functional group on the polymer backbone, so to illustrate my point let me just explain this with this cartoon, so if one makes a film with poly-olefin PE or PPE versus one makes another film with a co-polymerized PE, co-polymerized FG monomer, so with a film with this polymer this surface is hydrophilic, whereas pure polyethylene surface is hydrophobic and if one puts a drop of water molecule on top of it, so the water molecule this being hydro will have a concave surface because it will not wet the polymer surface, whereas for this kind of polyolefin with a functional group if one puts a water on it, so it will be hydrophilic and it will have a shape like this, so in this case the water will wet the surface, that means it will spread over a larger area of the polyolefin co-polymer surface, whereas water will be limited because this being hydrophobic the water will just have a minimum surface contact with this polyethylene or polypropylene surface and one can do a lot of experiments to demonstrate the wetness of the surface and one is called contact angle measurement, where they measure this angle between the water surface and the polymer which is called the contact angle that will give some indication as to how wet this surface or to what extent the functional monomer has been incorporated in the catalyst, so now this provides the basic platform based on which further development of these two polymerization, one is olefin with alpha olefin and olefin with alpha olefin bearing functional monomers where to be done, now when one talks about this polymerizing olefin and olefin with alpha olefins or one talks about polymerizing olefin and olefin with functional monomers which as a functional group using the catalyst which is Ziegler-Nut catalyst or metallocene catalyst, then the challenges which one faces are different. For example, if one were to consider this case of polymerizing olefin with the functional group, then the problem which one faces is that these functional group bearing oxygen, nitrogen and sulfur atoms they compete in binding to the vacant site of this catalyst. Each of these catalysts would have vacant site may be depicted by this metallocene also they have a vacant site, so they compete the functional group competes with binding to this vacant site as well as of the olefin and the olefin of the functional group, and it so happens that this functional group binding to the Lewis acidic metal center these outweighs the binding of the olefin to the vacant site, so these binds over here and as a result the functional group poisons the catalyst. As a result the functional group poisons the catalyst both the functional group and olefin might compete for the free coordination sites for the site, thus the functional group acts as a poison for these catalysts. So, what happens is this functional group binds more strongly to this Lewis acidic site over here as well as over here and it poisons the metallocene catalyst and does not allow the polymerization, so that is a nascent challenge for this type of copolymerization processes, and what it turns out that this poisoning of the catalyst poisoning by this functional group is more prominent for Ziegler-Natter catalyst than for metallocene catalyst. Catalyst poisoning is more prominent for Ziegler-Natter catalyst for metallocene catalyst, so this is an interesting observation that in both the cases in this case as well as this poisoning do happen, but the poisoning of Ziegler-Natter catalyst is more acute and more prominent and wins over and taking advantage of this process Weymouth in 1992 reported the following polymerization where one could do polymerization of alpha olefins and bearing functional monomer. So, what Weymouth did taking advantage of this process, Weymouth did homo polymerization of just this functional group using metallocene catalysts. So, the Weymouth chemistry using Cp star to zirconium methyl boron C6 F5 O3 and this is called Jordan's cation Weymouth polymerized this heteroatom bearing functionalized alpha olefin. So, this was a great discovery a belt on which people went back and started working on the copolymerization. Even though this is a homo polymerization alpha olefin bearing functional group, this was a big discovery. This was a big discovery by itself, because now this was reported by Weymouth in 1992. What Weymouth demonstrated is that these metallocene catalysts demonstrated that these metallocene catalysts can homo polymerize alpha olefins and the functional group did not poison the metallocene catalyst this metallocene catalyst and was able to give the homo polymer bearing functional group. So, this was a very important and interesting discovery which sort of led way to the parent problem. The parent problem was of being able to copolymerize first ethylene with alpha olefin and then ethylene with alpha olefin bearing functional group. So, this copolymerization was further developed on the backbone of Weymouth's results which could polymerize alpha olefins bearing functional group. So, with this we come to the end of today's lecture and what we have demonstrated is the fine fit of organometallic chemistry in how the organometallic chemistry, organometallic catalysts triumph over the requirement for producing different types of polyethylene polymer and we had seen that how these catalysts evolved on going from polymerizing ethylene or propylene by themselves which are called homo polymerization and then providing several grades of the homo polymerized products and then finally how the need for developing copolymer with more polar surfaces and polyolefin backbone was developed and addressing that the challenges which remain was this functional groups were actually poisoning the catalysts, but one observation was made that the extent of poisoning was more significant for Ziegler-Nutta catalysts heterogeneous than for metallocene catalysts and taking advantage of this knowledge what Weymouth first did is paved way for developing this further with copolymerization and what Weymouth showed was taking a metallocene catalyst he could successfully homo polymerized alpha olefins bearing amine functional group albeit in modest yield. So, with this I come to the conclusion of today's lecture we are going to be talking more about this homo polymerization and a copolymerization with olefins and alpha olefins and olefins and alpha olefins bearing functional group how this really took off and how more improved catalysts were developed for the copolymerization process all of these interesting stuff when we meet next until then good bye and thank you.