Polybutadiene living polymerization

Block copolymers can often offer properties that are unattainable with simple blends or random copolymers. This led to many efforts to combine dissimilar materials, like hydrophilic with hydrophobic, or hard with soft segments, as was shown earlier. A recent paper" describes the formation of block copolymers containing helical polyisocyanide and an elastomeric polybutadiene. Compound [(7 -C3H5>-Ni(OC(0)CF3)]2 was used to carry out living polymerization of butadiene and then followed by polymerization of rm-butyl isocyanide to a helical polymer. 

Anionic polymerization of polystyrene takes place very rapidly- much faster than free radical polymerization. When practiced on a large scale, this gives rise to heat transfer problems and limits its commercial practice to special cases, such as block copolymerization by living reactions. We employ anionic polymerization to make tri-block copolymer rubbers such as polystyrene-polybutadiene-polystyrene. This type of synthetic rubber is widely used in the handles of power tools, the soft grips of pens, and the elastic side panels of disposable diapers. 

It has been shown recently (10) that such block structures could be tailored precisely by the general method summarized hereabove. It is indeed possible to convert the hydroxyl end-group of a vinyl polymer PA (f.i. polystyrene, or polybutadiene obtained by anionic polymerization terminated with ethylene oxide),into an aluminum alcoholate structure since it is well known that CL polymerizes in a perfectly "living" manner by ring-opening insertion into the Al-0 bond (11), the following reaction sequence provides a direct access to the desired copolymers, with an accurate control of the molecular parameters of the two blocks ... 

The first approach Is to polymerize small amounts of 4-vlnyl pyridine on to the ends of anionic living polybutadiene, mono- or difunctional, to produce what are essentially AB or ABA block copolymers (equation 5). Materials possessing values of n typically averaging about 3 have been prepared and shown to produce solids when quaternlzed with benzyl bromide. The result of... 

Unpublished work of Halasa and co-workers 31) on the study of live chain ends using 13C-NMR as a probe into their structures has led to some interesting new findings. These workers studied the lithium live ends of polybutadiene in the presence of a new polar modifier, dipiperi-dylethane (DPE). This modifier forms a complex with n-BuLi which initiates the polymerization of 1,3-butadiene to give polymer having 100% 1,2 microstructure. 

The living character of organolithium polymerizations makes such processes ideally suited for the preparation of pure as well as tapered-block copolymers. Diene-olefin pure-block copolymers have become important commodities because of their unique structure-property relationships. When such copolymers have an ABA or (AB) X [A = polyolefin, e.g., polystyrene or poly(a-methylstyrene) B = polydiene, e.g., polybutadiene or polyisoprene and X = coupling-agent residue] arrangement of the blocks, the copolymers have found use as thermoplastic elastomers (i.e., elastomers that can be processed as thermoplastics). 

The first block (polybutadiene or polystyrene) is prepared by anionic polymerization, under high vacuum, in THF dilute solution (less than 5%), at low temperature (—70 °C) with cumylpotassium as initiator. Then, the living polymer is transformated into a hydroxylated polymer (PV—OH) by addition of ethylene oxide under vacuum, or into a carboxylated polymer (PV-COOH) by addition of carbon dioxide under vacuum. 

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