Monomer configuration

The first stereochemical analysis of the polymerization mechanism of unsaturated monomers was proposed by Arcus 30 years ago (58, 269). The diaste-reomeric relationships within a single chain may be connected to monomer configuration by two factors the type of addition to the double bond (cis or trans) and the way in which successive monomer molecules approach the growing chain. For a CHA=CHB olefin the relationship between the stmcture of the monomer and that of the adding monomeric unit is illustrated in Scheme 22 (31), where cis or trans addition indicates that the new bonds are formed in the same half-space or in the two opposite half-spaces, provided there is no rotation aroimd the central C—C single bond. 

This chapter showcases the synthetic strategies for both nonsubstituted and substituted polythiophenes. To date, many of these synthetic procedures are still being used for traditional polymerizations of PTs and PSTs, while variations in the synthetic methodology are dependent upon the monomer configuration or end-group functionality of the polymer. For instance, modifications to the catalyst, particularly ligand exchanges in Pd and Ni... 

It is clear that asymmetry introduction in radical polymerization is more difficult because this reaction has much less stereospecific action on the growing end group than ionic polymerization. But optically active polymer which has some asymmetric center in the main chain, can be apparently synthesized using the asymmetry of monomer configuration (molecular asymmetry). 

Gerken and Ritchey [190] reported the C-NMR of series of acrylonitrile-methyl methacrylate (A/M) copolymers and determined the copolymer microstructure. They reported the configuration probabilities of A/M copolymers and Bernoullian statistics were found to describe the monomer configuration, a result in conflict with the conclusions of Pham [191]. Gerken and Ritchey [190] assigned the resonance lines of carbonyl and nitrile carbons to different triad cotactic sequences on the assumption that M and A monomer units have the same sensitivity to the tacticity of an adjacent A monomer unit. Also they did not calculate cotactic triad fractions from C-NMR spectra and did not compare experimental cotactic triad fractions with those expected from configurational probabilities have been made. 

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