Isoprene Ziegler polymerization

Isoprene Ziegler-Natta-catalyzed chain polymerization Car tires (55%), mechanical goods, sporting goods, footwear, sealants, and caulking compounds... 

Coordination polymerization of isoprene using Ziegler-Natta catalyst systems (Section 6 21) gives a material similar in properties to natural rubber as does polymerization of 1 3 butadiene Poly(1 3 buta diene) is produced in about two thirds the quantity of SBR each year It too finds its principal use in tires... 

From the time that isoprene was isolated from the pyrolysis products of natural mbber (1), scientific researchers have been attempting to reverse the process. In 1879, Bouchardat prepared a synthetic mbbery product by treating isoprene with hydrochloric acid (2). It was not until 1954—1955 that methods were found to prepare a high i i -polyisoprene which dupHcates the stmcture of natural mbber. In one method (3,4) a Ziegler-type catalyst of tri alkyl aluminum and titanium tetrachloride was used to polymerize isoprene in an air-free, moisture-free hydrocarbon solvent to an all i7j -l,4-polyisoprene. A polyisoprene with 90% 1,4-units was synthesized with lithium catalysts as early as 1949 (5). 

In the mid-1950s, the Nobel Prize-winning work of K. Ziegler and G. Natta introduced anionic initiators which allowed the stereospecific polymerization of isoprene to yield high cis-1,4 stmcture (3,4). At almost the same time, another route to stereospecific polymer architecture by organometaHic compounds was aimounced (5). 

Conjugated dienes are among the most significant building blocks both in laboratories and in the chemical industry [1], Especially, 1,3-butadiene and isoprene are key feedstocks for the manufacture of polymers and fine chemicals. Since the discovery of the Ziegler-Natta catalyst for the polymerizations of ethylene and propylene, the powerful features of transition metal catalysis has been widely recognized, and studies in this field have been pursued very actively [2-7]. 

Discuss the use of homogeneous versus heterogeneous reaction conditions for the coordination and traditional Ziegler-Natta polymerizations of propene, isoprene, styrene, methyl methacrylate, and n-butyl vinyl ether. 

The cationic nature of Ziegler catalysts have been proposed by Sinn, Winter and Tirpitz (90) who found that the polymerization of styrene, of vinylethers, of butadiene and of isoprene by Ziegler catalysts required the presence of trace amounts of proton-active substances. These same cationic catalyst species isomerized heptene and isoheptene. No definite results could be obtained for propylene and it... 

The all-cis structure of natural rubber is vita) to its elasticity. The all-trans compound is known and it is hard and brittle. Though dienes such as isoprene can easily be polymerized by cationic methods, the resulting rubber is not all-cis and has poor elasticity and durability. However, polymerization of isoprene in the Ziegler-Natta way gives an all-cis (90-95% at least) polyisoprene very similar to natural rubber. 

For instance, in the field of elastomers, alkyllithium catalyst systems are used commercially for producing butadiene homopolymers and copolymers and, to a somewhat lesser extent, polyisoprene. Another class of important, industrial polymerization systems consists of those catalyzed by alkylaluminum compounds and various compounds of transition metals used as cocatalysts. The symposium papers reported several variations of these polymerization systems in which cocatalysts are titanium halides for isoprene or propylene and cobalt salts for butadiene. The stereospecificity and mechanism of polymerization with these monomers were compared using the above cocatalysts as well as vanadium trichloride. Also included is the application of Ziegler-Natta catalysts to the rather novel polymerization of 1,3-pentadiene to polymeric cis-1,4 stereoisomers which have potential interest as elastomers. 

Only single insertions into an Al-C bond occur for propene and higher alkenes and this is utilized for catalytic dimerization of propene as illustrated in Scheme 3. Insertion of propene into an Al-C bond of "PrsAl followed by )3-hydride elimination yields an aluminum hydride and 2-methylpent-l-ene. Insertion of propene into the Al-H bond regenerates "PrsAl. Thermal cracking of 2-methylpent-l-ene gives isoprene, which is subsequently polymerized with a Ziegler-Natta catalyst to form the synthetic rubber, cA-1,4-polyisoprene. 

It is possible to control the type of polymer produced. This is best illustrated with polymerization of the monomer isoprene 2-methyl-1,3-butadiene. The Ziegler-Natta catalyst, consisting of a titanium tetrachloride... 

Chart 2.1. The negative-tone resists that were first used in semiconductor manufacturing were based on a matrix resin of synthetic rubber prepared by Ziegler-Natta polymerization of isoprene followed by acid-catalyzed cycliza-tion to improve the mechanical properties. This cyclized rubber was rendered photosensitive by addition of a bisarylazide that undergoes photolysis to produce a bisnitrene. The nitrene reacts with the cyclized rubber to create in-termolecular cross-links that render the exposed areas insoluble. 

The structure of the polymer obtained in the polymerization of butadiene and isoprene with heterogeneous Ziegler-Natta catalysts depends on the nature of the monomer, catalyst system, and reaction conditions. Previously reported results are reviewed and a mechanism is proposed for the stereoregulated polymerization of conjugated dienes. The polymerization of cyclopentadiene with LiAlH -TiCl4 or LiAlR4-TiCl4 catalyst system yields a readily oxidized polymer for which a 1,2-structure is proposed. 

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