Special polymers from dienes

There are many reports in the literature of preparations of polymers from various other substituted dienes. Most have no commercial significance. Some are, however, interesting materials. An example is a polymer of 2-f-butyl-l,3-butadiene formed with TiCla and either alkylaluminum or aluminum hydride catalysts [132]. The polymer is crystalline and melts at 106°C. It can be dissolved in common solvents. Based on X-ray data, the monomer placement is high cis-1,4. 

Poly(carboxybutadiene)s also forms with coordination catalysts [133-135]  

X-ray crystallography [133-135] showed that the placement is fraws-isotactic. 

Based on the mode of packing of the chains in the crystalline regions and from the encumbrance of the side groups in relationship to the main chain, an erythro configuration can be assigned [134]. The polymers, therefore, are fraws-eryf/iro-isotactic. 

Polymerization of 1,3-pentadiene can potentially result in five different insertions of the monomers. These are 1,4-cis, 1,4-trans, 1,2-cis, 1,2-trans, and 3,4. In addition, there are potentially 3-cis-l,4 and 3 trans-1,4 stmctures (isotactic, syndiotactic, and atactic). Formations of trans-1,4 isotactic, cis-1,4 isotactic, and cis-1,4 syndiotactic polymers are possible with Ziegler-Natta catalysts [136-138]. Amorphous polymers also form that are predominantly cis-1,4 or trans-1,4, but lack tactic order. Stereospecificity in poly (1,3-pentadiene) is strongly dependent upon the solvent used during the polymerization. Thus, cis-1,4 syndiotactic polymers form in aromatic solvents and trans-1,2 in aliphatic ones. The preparations require cobalt halide/aluminum alkyl dichloride(or dialkyl chloride) catalysts in combinations with Lewis bases. To form a trans-1,4 structure, a catalyst containing aluminum to titanium ratio close to 5 must be used [139]. 

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Synthetic Rubbers. Synthetic rubbers are polymers with rubberlike characteristics that are prepared from dienes or olefins. Rubbers with special properties can also be prepared from other polymers, such as polyacrylates, fiuorinated hydrocarbons, and polyurethanes. 

For specific papers on oligomers prepared from dienes, special mention is made to French s [8] and Schnecko s [9] works (126 and 68 references respectively). Then, we can mention a special study by Entelis [10,11] based on the functionality and the molecular distribution of telecheUc polymers. 

In the present paper we pay special attention to block polymers with polypropylene and polyethylene as the initial anionic block. However, both crystalline and amorphous block polymers of ethylene and propylene, butadiene, and several other olefins and dienes have been made by the AFR technique. The second or free radical block has been made from 4-vinylpyridine, 2-methyl-5-vinylpyridine, and mixtures with other monomers, as well as a number of acrylic monomers. Vinyl chloride, vinylidine chloride, vinyl acetate, and several related monomers have not been successfully copolymerized. 

Many hundreds of diene polymers were investigated for their suitability as elastomers. Only three of these have achieved widespread commercial acceptance butadiene-styrene copolyipers, butadiene-aciylonitrile copolymers, and poly-2-chlorobutadienes. Other essentially non-diene elastomers such as butyl rubber from isobutene, Thiokol from ethylene dihalides and polysulfides, and silicones have become important for special applications. 

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