Polymerization, elastomer synthesis catalysts

Several other methods for controlled radical polymerization have been developed and should be applicable to elastomer synthesis (Matyjaszewski, 1998, 2000). One of the other most important systems for controlled radical polymerization is atom transfer radical polymerization (ATRP) (Matyjaszewski and Xia, 2001). A transition metal (Mt) catalyst participates in an oxidation-reduction equilibrium by reversibly transferring an atom, often a halogen, from a dormant species (initiator or polymer chain) as shown below. 

Dioctyltin diisooctylthioglycollate catalyst, PU two-pack coatings Dibutyltin bis (laurylmercaptide) catalyst, PU elastomers Ferric acetylacetonate N-Hydroxyethy I pi perazi ne catalyst, purified terephthalic acid polyesters Manganese acetate (ous) catalyst, PVC suspension polymerization Lauroyl peroxide catalyst, pyridine synthesis Cobaltocene... 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

The synthesis of a unique class of polymers with a phosphorus-nitrogen backbone Is described, focusing on poly-(dlchlorophosphazene) and poly(organophosphazene) elastomers. Melt and solution polymerization techniques will be Illustrated while briefly Indicating the role of catalysts which give significantly Improved rates of conversion and reproducibility In polymer properties. 

Precaution Extremely flamm. sol ns. (> 20%) will ignite spontaneously in air ignites on contact with water or CO2 may cause potentially explosive polymerization of styrene NFPA Health 3, Flammability 4, Reactivity 2 Uses Solution polymerization initiator for polyolefin elastomers polymerization catalyst for food-contact polybutadiene for repeated use lithiation reagent Grignard-type reagent intermediate in prep, of lithium hydroxide org. synthesis reagent for metallation of org. compds. rocket fuel components to generate tetrahydrofurans from (tributylstannyl) methyl ethers... 

Uses Catalyst in mfg. of rubbers and plastics based on styrol-butadiene, polyisoprene, and polybutadiene initiator in anionic polymerization of styrene and conjugated dienes, thermoplastic elastomers organic synthesis... 

Moineau, G., et al. (2000). Synthesis of fully acrylic thermoplastic elastomers by atom transfer radical polymerization (ATRP). 2. Effect of the catalyst on the molecular control and the rheological properties of the triblock copol5mers. Macromol. Chem. Phys., 20/(11) 1108-1114. 

Coordination polymerization also produces high sterospecificity in the polymerization of alkenes. Isotactic and syndiotactic polymers can be obtained by appropriate choice of the catalyst components although such polymers are not useful as elastomers. However, Ziegler-Natta catalysts are used to produce EPR and EPDM rubbers. (Coordination polymerization is important for the synthesis of linear polyethylene and isotactic polypropylene which find extensive utility as plastics.) The Symposium paper by Su and Shih describes the synthesis of propylene-l-hexene block copolymers using several catalysts based on titanium and aluminum components. 

As a result of polymerization of 1,3-butadiene and its derivatives one obtains synthetic rubbers (elastomers) whose properties depend on the structure of the formed products. The stereospecific Ziegler-Natta catalysts offer new opportunities for the synthesis of rubbers with a defined structure. It turned out that by choosing an appropriate catalyst one can be obtain the following polymer structures cis-1.4, trans-1.4, isotactic 1.2, and syndiotactic 1.2, all in a relatively pure form. The influence of the catalyst structure on the stereospecific polymerization of butadiene is shown in Table 8.11. 

Because of their high technical properties, polyamide-based thermoplastic elastomers have attracted a lot of interest and their synthesis has been attempted via various polymerization techniques. On the industrial scale, the major companies are producing TPE-A via one- and two-step thermal polymerization processes. Many parameters have to be adjusted to ensure optimal reaction efficiency, including catalyst nature and content, temperature, vacuum level and stirring rate. Obviously, all these parameters are also dependent on the nature of the raw materials used, since some polyamide/polyether pairs, depending on their structure and/or the nature of their end-groups, are easier to prepare than others. 

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