Price 12 Amorphous Solids

Whatever the method of control may be it seems evident that it is by no means completely efficient for the solid polymer is always a rather small fraction of the total. Price believes, presumably because any optical activity tends to be concentrated in the crystalline phase, that the amorphous and crystalline polymers are products of two different reactions, one in solution and the other heterogeneous (27). While this view is not impossible, it could be argued that solution reaction might be expected to lead to either inversion or retention of configuration and, hence, optically active polymer. Furthermore, some reports suggest rather strongly that the distinction between the two types of polymer is a rather arbitrary one based in part on polymer symmetry and in part on molecular weight. 

Propylene oxide has an asymmetric carbon atom. The normal commercial epoxide is a racemic mixture of the d- and 1-isomers. Osgan and Price did extensive work with both the 1-propylene oxide and the d,l-propylene oxide in both potassium hydroxide and ferric chloride/propylene oxide-initiated polymerizations. Their results are summarized in Table 5 (48). C. C. Price and coworkers first demonstrated that polymerization of pure 1-propylene oxide with an anhydrous potassium hydroxide (solid KOH) initiator led to a crystalline, rather than the usual amorphous, liquid, polymer. After extensive study by a number of researchers (69), this polymerization was shown to proceed by a stepwise anionic mechanism. The uses found for polymers of propylene oxide largely have been those requiring the amorphous polymer in elastomeric applications. Stereospecificity, however, has proved to be a key tool in understanding the polymerization mechanisms. 

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