 Welcome to this course on Transitional Metal Organometallics in Catalysis and Biology. We have been discussing about olefin polymerization, particularly we have looked into ethylene polymerization as well as propylene polymerization in the last few lectures, and there we have looked mainly into homopolymerization of these two monomers, ethylene and propylene. What it means that ethylene polymerizes to give polyethylene and propylene polymerizes to give polypropylene, and these are what is called homopolymerization. Now in the last class, we have also looked into the other possibilities of doing copolymerization. Copolymerization can be of two different monomers. They can be both olefins like ethylene and propylene, ethylene one hexane or ethylene alpha olefins and so on and so forth, or they can be of ethylene and alpha olefin bearing functional groups. Now the main challenges which we have encountered is that these particularly for ethylene alpha olefin polymerization, the main challenges which was encountered was the rate of polymerizations are not the same for the two monomers. For example, for Ziegler-Natter catalysis as well as the metallocene catalysis, the ethylene homopolymerization is much higher at a much higher rate than the alpha olefin homopolymerization, whereas in metallocene catalysis, the difference is not that extent. However, still it is less acute than the difference what is present in Ziegler-Natter catalysis, but still nonetheless they are there that the rate of homopolymerization of ethylene is higher than the rate of homopolymerization of alpha olefins. Now when it comes to copolymerization of ethylene with alpha olefins bearing functional group, it is even more challenging because the hetero atoms of the functional group compete with the ethylene binding which occurs at the polymerization site. As a result, the presence of functional group also poisons the catalyst for further polymerization, and this poisoning is more significant for a heterogeneous Ziegler-Natter type catalyst. Then it is for metallocene based ones, and that is what was the main drawback is that the polymerization of functional monomers were in fact poisoning the catalyst. However, nonetheless in the last lecture, we had seen this nice example where for zirconizing catalyst weymouth successfully homopolymerize heteroatom bearing functional groups. Like that it goes and this is the repeat unit. The good thing is this was reported by weymouth in 1992, and what this work is about is homopolymerization of alpha olefins bearing functional group using the catalyst, and these were isotactic, albeit in modest yield. This is an interesting result because this for the first time showed that for using metallocene catalyst, this poisoning of the metallocene catalyst with this kind of functional group does not happen that significantly, and one is able to obtain this homopolymerization of alpha olefin functionalized polymer in large yield. That is a significant discovery, and that led to the discovery of an important catalyst which are called half sandwich complexes, and which are called constrained geometry catalyst half sandwich complexes of Cp metal amide types exhibited high catalyst activity for ethylene homopolymerization and ethylene copolymerization with alpha alkenes. This was an interesting discovery, the weymouth discovery way back in 1992, which said that the metallocene based complexes are indeed tolerant towards functional group, and as a result further modification led to extremely active half sandwich complexes, which showed very high catalyst activity for ethylene homopolymerization as well as ethylene alpha olefin copolymerization. Let me illustrate this with a particular example, where R equals CH2PH, and here titanium is in plus 4 state, and this gives the following Me2Si, Tb2, titanium, actually there is a activation of the methyl group as is shown here, overall there is a positive charge, and the benzyl group is abstracted on boron, which has a negative charge, so overall this is a titanium 4 compound, but it is a cationic in nature, and there is this anion, and in the course of formation of this the first is the benzyl abstraction, which goes on to boron as is observed over here, and the second is elimination of minus PHCH3, one benzyl good abstracts activates a methyl proton, the other one activates a methyl proton, and eliminates as toluene to give this cationic complex, now this cationic complex is extremely good catalyst both for ethylene as well as for polyethylene, which ethylene it could produce molecular weight get then 10 to the power 6 Dalton, and ultra high molecular weight polyethylene, and with olefins it could do copolymerization, so this is extremely good catalyst for polyethylene copolymer 1 hexane in greater than 30% yield, this is 30% incorporation and hexane base then 70% incorporation, so extremely good catalyst for polyethylene as well as alpha olefin incorporation, and this catalyst is called constrained geometry catalyst, it has three features, the first one is electron deficiency, this species has total valence electron less than equal to 14, so extremely electron deficient species, the second there is a free coordination site in presence of in vicinity of a growing polymer chain, and third is a positive charge complex, and this prevents suppresses deactivating dimerization process reactions, and facilitates olefin coordination, so these are very important notable features of this constrained geometry catalyst that is extremely electron deficient then it has a free coordination site and also being positively charged that it suppresses deactivation pathway and facilitates olefin burning, and this is so good that it could produce ultra high molecular weight polyethylene polymer of about a million molecular weight huge molecular weight, and also it could produce ethylene 1 hexane copolymer with about 70% incorporation of ethylene and 30% incorporation of polyethylene, so this is an important example and this was reported by Marks, Professor Tobin Marks in 1997 extremely good catalyst, and the fourth feature of this is that it has a steric bulk that also takes care for this high molecular weight polymer, this is illustrated or just spoken about, and another important quality is that so we have spoken about copolymerization of two units where this constrained geometry could polymerize ethylene as well as alpha olefin, and then a tar polymer or polymerization of three units, an important tar polymer is E P D M is obtained from ethylene, propylene and non conjugated diene example is 1,4 hexadiene, and these are polymerized by VOCl3 based Ziegler-Nurter catalyst, catalyst as well as metallocene catalyst, E P D M behaves as an elastomer similar to natural rubber in properties, so here we have spoken about in the previous slide we have spoken about the polymerization of two different monomers, one is alpha olefins and ethylenes, and then now we are talking about polymerization of three different monomers, one is ethylene another is alpha olefin and non conjugated diene, three different monomers and these are done can be done both as a heterogeneous way where it is VOCl3 based Ziegler-Nurter catalyst as well as by metallocene catalyst, these E P D M or the tar polymer are elastomeric in nature and behave similar like that of the rubbers, so this is an interesting example where three different monomers could be polymerized to obtain something which is of natural rubber, so in this regard another interesting property which we will be talking about is that of polycyclo olefins, now they can be polycyclo olefins can be obtained in two ways, polycyclo olefins can be obtained in two ways and the first is important it should be a suitable catalyst to be chosen such that metathesis reaction is suppressed and then this was reported by Kashiwawa in 1988 and the reaction is given as follows, so this the first is a dill solder reaction first is a dill solder reaction to give this multi cyclic species as is shown here and that in reaction with ethylene VOCl2, 83Cl3 or metallocene catalyst gives this cyclic polyolefin which is given over here of ethylene and ethylene over here and what is seen over here there are two things first is the polymerization of the two units one unit is this alpha olefin and the other unit, so these two units are shown over here this being the first sorry these two units are shown over here this being the first and this being the second ethylene unit and this being the first these two got copolymerized to give this polycyclo olefins to give polycyclo olefin polymers and the property wise important properties they are thermostable one is thermostable the second is transparent and third is minimally birefringent and advantage over polymethacylates and polycarbonates and used used for cds compactics and magnetic storage materials, so these polycyclo olefins again are copolymerization of two olefins one is cyclic another is ethylene to give this and they have important properties like thermostable transparent, minimally birefringent and also used for cds and magnetic storage applications, so with these we come to the end of today's discussion in today's class we have looked into the copolymerization strategy of olefins and alpha olefins and the main challenges arise in this area for two from two aspects one is that the rate of polymerization of the two monomers one is ethylene as well as the other is alpha olefins are different and it turns out that alpha olefins are more slower than the olefins in terms of conventional catalyst however in using metallocene catalyst one can have less acute difference of reactivity of alpha olefins as well as ethyliens and what we have discussed today is about the advent of constraint geometry catalyst which could produce ultra high molecular with poly ethylene of about higher than one million way Dalton and also it could successfully copolymerize ethylene and hexane with about higher incorporation about 70 percent or greater incorporation of hexane and about 30 percent or so incorporation of ethylene in its copolymer we have also spoken about moving going beyond the polymerization of two monomers to polymerization of three monomers and we have spoken about tar polymer from ethylene propylene and hexane and then finally we have looked into poly cyclo olefins which are usually which are material of importance for a magnetic applications they are thermostable transparent and minimally by by refrigerant refrigerant and they are produced by two pathways we have discussed one of them which involves using catalyst that will not promote ring opening metathesis reactions and hence first there we have seen one example by kasharva where first these all the reaction and subsequent polymerization with the vio ethyl OET CL2 and presence of aluminum ethyl reagent or mantleosine catalyst that could give these poly cyclo olefin polymers so with these we come to an end of today's class more on discussion about various applications of these copolymerization with olefins and alpha olefins as well as with functional monomer as we continue the discussion in the next class till then goodbye and thank you