Synthesis, elastomer considerations

AGE-Gontaining Elastomers. The manufacturing process for ECH—AGE, ECH—EO—AGE, ECH—PO—AGE, and PO—AGE is similar to that described for the ECH and ECH—EO elastomers. Solution polymerization is carried out in aromatic solvents. Slurry systems have been reported for PO—AGE (39,40). When monomer reactivity ratios are compared, AGE (and PO) are approximately 1.5 times more reactive than ECH. Since ECH is slightly less reactive than PO and AGE and considerably less reactive than EO, background monomer concentration must be controlled in ECH—AGE, ECH—EO—AGE, and ECH—PO—AGE synthesis in order to obtain a uniform product of the desired monomer composition. This is not necessary for the PO—AGE elastomer, as a copolymer of the same composition as the monomer charge is produced. AGE content of all these polymers is fairly low, less than 10%. Methods of molecular weight control, antioxidant addition, and product work-up are similar to those used for the ECH polymers described. 

At AWE, the Lewis acid-catalyzed bulk polymerization route has been the main synthesis route to poly(m-carborane-siloxane) elastomers. Our selection has been based on considerations of safety, availability of key reagents, and ease of scale-up operations. An understanding of the physical and chemical properties of these materials, and how these properties can be modified through the synthesis process, is essential in order to develop materials of controlled characteristics. 

Chain extenders Diols and diamines are generally used as chain extenders in PU industry and choice of chain extender influences elastomer properties considerably. The standard diol chain extender used for the synthesis of PU elastomer is 1,4-butane diol (BDO). Compared with a diol, better physical properties usually result when a diamine is employed as an extender. This is probably due to the introduction of urea linkages which enter into strong hydrogen bonded interactions. A diamine is usually chosen as the chain extender when a relatively unsymmetrical diisocyanate is employed. Diamines also function as efficient catalysts in addition to chain extenders. 

The present book is organized into 6 chapters. Chapter 1 describes general aspects on the chemistry of polyurethane elastomers their origins and development, the principles and synthesis mechanisms, as well as general considerations on the main chemical parameters that define such materials, i. e. diisocyanate, macrodiol and chain extender. Selected considerations regarding the reactivity of diisocyanates, the hydrogen bonding and its dynamic and quantum aspects are also discussed in this chapter. 

It will be realized from Chapter 1 that in urethane elastomer formation from liquid components there is the possibility of several reactions occurring simultaneously during a prepolymer or one-shot process, and that the relative proportion of one to the other will affect the overall properties of the final polymer. Thermoplastic and millable urethanes are not, during their processing and fabrication stages, subjected to the type of catalysis discussed in this chapter during their polymer synthesis operations, however, reaction rate-structure considerations will apply. 

Synthesis. Polybutadiene (PBD) and polydimethylsiloxane (PDMS) were selected as the elastomers. The synthesis of the corresponding AB and ABA block copolymers is shown in Schemes 1 and 2 respectively. The synthesis of the AB and ABA-PBD-block copolymers does not require the use of the acetal initiator 1 and could easily be carried out using simple one- and two-ended lithium initiators. However, the merit of the present synthetic method is that AB, ABA and (AB)a copolymers may be prepared from the same precursor, 12. Similar considerations apply for the PDMS-PMMA copolymers. The use of 1,1-diphenylethylene as a capping agent is needed to prevent nucleophilic attack of the reactive allylanion of living PBD on the ester group of MMA.1 The use of the masked OH initiator 1... 

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