Liquid Polybutadiene

Low molecular weight liquid homopolymers of 1,3 butadiene, also some liquid copolymers, find industrial uses in many applications. These materials can range in molecular weights from 500 to 5,000 depending upon the mode of polymerization. Liquid polybutadienes formed by cationic polymerizations are high trans-1,4 content. Such materials find applications in industrial coatings. They are usually prepared with Lewis acids in chlorinated solvents. When the reactions are catalyzed by AlCl3 at 78C, two types of polymers form [108]. One is soluble and the other is insoluble, depending upon the extent of conversion. AlCl₃, AlBr₃, and BF₃–Et₂O produce polymers with the same ratios of trans-1,4 to 1,2 adducts. These range from 4 to 5. Polymerizations carried out in ethylene chloride [108] catalyzed by TiCl4 yield products with lower ratios of trans-1,4 to 1,2 adducts. The ratios of the two placements are affected by the solvents. They are also affected by additions of complexing agents, such as nitroethane and nitrobenzene [108]. The changes, however, are small. Hydroxyl-terminated liquid polybutadienes are prepared for reactions with diisocyanates to form elastomeric polyurethanes (see Chap. 6). Such materials can be prepared by anionic polymerizations as “living” polymers and then quenched at the appropriate molecular weight. These polybutadienes can also be formed by free-radical mechanism. The microstructures of the two products differ, however, and this may affect the properties of the finished products. To form hydroxyl-terminated polymers by free-radical mechanism, the polymerization reactions may be initiated by hydroxyl radicals from hydrogen peroxide. A new approach to preparation of hydroxyl-terminated liquid polybutadiene is to use a cyclic monomer, 1,5-cyclooctadiene, a ruthenium metathesis catalyst (see Chap. 5, Grubbs catalysts in section on metathesis ring opening polymerization) and an acetate functionalized chain transfer agent [109, 110]. The acetate-functionalized chain transfer agent is cis-2-butene-1,4-diacetate. The reaction can be carried out without solvent and proceeds at 50C over 6 h under an inert gas purge [111]. The acetate protecting groups provide compatibility with the ruthenium catalyst. Subsequent to polymerization the acetate groups can be converted to hydroxyl end groups with the aid of a base, like sodium methoxide. Liquid polybutadienes that are high in 1,2 placement are also available commercially. These range from reactive polymers containing approximately 70% of vinyl groups to very reactive ones containing more than 90% of 1,2 units. The materials are formed by anionic polymerization with either sodium naphthalene, or with sodium dispersions, or with organolithium initiators in polar solvents. Carboxyl group terminated liquid polybutadienes are predominantly used as modifiers for epoxy resins (Chap. 7). They are formed by anionic mechanisms in solution with organolithium catalysts like diphenylethanedilithium, butanedilithium, isoprene lithium, or lithium methylnaphthalene complexes. Cyclohexane is the choice solvent. The reaction is quenched with carbon dioxide to introduce the terminal carboxyl groups.

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مواضيع ذات صلة

Synthetic Polyisoprenes

High Molecular Weight Polybutadiene

Polybutadiene

Ionomers

Copolymers of Ethylene with a-Olefins and Ethylene with Carbon Monoxide

Ethylene and Propylene Elastomers

Poly (4-methyl pentene-1)

Polyisobutylene

Syndiotactic Polypropylene

Manufacturing Techniques

Polypropylene

Materials Similar to Polyethylene