Highly stereoregular copolymers

Neutral lanthanide-series metallocenes exhibit the remarkable ability to polymerize polar monomers such as methyl methacrylate to highly stereoregular polymers of extremely narrow molecular weight distribution (Mw/Mn 1) (equation 14). It is possible to prepare block copolymers of ethylene and poly(methyl methacrylate) by first adding MMA to Cp 2SmMe to produce a PMMA segment followed by addition of ethylene the reverse order of addition fails to give block materials because the ethylene monomer cannot insert into the enolate. 

Preparation of Random, Block and Graft Copolymers of High Stereoregularity and their Characterization... 

Specifically chemical considerations are especially evident in Chap. 7, where copolymers and stereoregular polymers are discussed. Since two monomers are required for the formation of a copolymers, the differences in their reactivity affects both the composition of the product and the distribution of components in it. Likewise, the catalysts that produce stereoregularity are highly specific, highly reactive, and poorly understood chemical reagents. 

Polymers account for about 3—4% of the total butylene consumption and about 30% of nonfuels use. Homopolymerization of butylene isomers is relatively unimportant commercially. Only stereoregular poly(l-butene) [9003-29-6] and a small volume of polyisobutylene [25038-49-7] are produced in this manner. High molecular weight polyisobutylenes have found limited use because they cannot be vulcanized. To overcome this deficiency a butyl mbber copolymer of isobutylene with isoprene has been developed. Low molecular weight viscous Hquid polymers of isobutylene are not manufactured because of the high price of purified isobutylene. Copolymerization from relatively inexpensive refinery butane—butylene fractions containing all the butylene isomers yields a range of viscous polymers that satisfy most commercial needs (see Olefin polymers Elastomers, synthetic-butylrubber). 

One could also imagine a complex that at one site will insert only one certain type of alkene due to high steric constraints (e.g. ethene) and a second alkene at the other site thus giving an alternating copolymer that may even contain stereoregularity, thus obtaining for instance an alternating norbomene/ethene copolymer [34],... 

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