Polymer nomenclature configuration

The nomenclature of regular polymers can denote stereochemical features if the CRU used is the configurational base unit [10], i.e. a CRU having one or more sites of defined stereoisomerism in the main chain of a polymer molecule [11]. Structure-based names are then derived in the usual fashion. The various stereochemical features that are possible in a polymer must first be defined. 

E3 = — + and E4 = - 7 where the + and - define the relative configuration of two adjacent monomer units in the polymer chain. In accordance with the nomenclature of Bovey (7), we call the sequence (+ +) isotactic, (+ -), or (- +) heterotactic, and (- -) syndiotactic. The transition probabilities between various states were defined for the four-parameter model (1). 

A second element of chirality is the configuration of the tertiary carbon atom of the growing polymer chain nearest to the metal atom. In fact, a new stereogenic center is formed in the growing chain at every propene insertion (Scheme 4). The standard Cahn—Ingold—Prelog R, S nomenclature jjg used here. 

For achiral metallocene-based catalysts Czv and achiral Q metallocenes in Chart 2) the chain-end control is present as the only stereocontrol mechanism. It derives from the presence of an asymmetric carbon atom on the last inserted monomer. The chirality R or 5) of this atom is related to the enantiotopic face of the olefin where the insertion took place (Scheme 34). In the NMR spectrum of the polymer we lose this kind of information, as two successive insertions of the re olefin face and two successive insertions of the si face produce the same m diad (see section II.G). As a consequence, we can observe only the relative chirality between consecutive inserted monomer units (5,5 or R,R as m diads and S,R or R,S as r diads) disregarding the absolute configuration of tertiary atoms. We prefer to use the re and si nomenclature indicating the stereochemistry of the methines in the polymer chain (Scheme 35), bearing in mind that the insertion of the re propene enantioface will produce an 5 configuration on the methine. 

We adopt the nomenclature of molecular spectroscopy to describe the excitation and relaxation processes in PPV derivatives, since the polymer photophysics is similar to the photophysics of large organic molecules [146]. Figure 22.11 shows schematically the configuration coordinate diagram of all... 

Configurationally chiral, optically active polymers having stereogerric centers in the side chain or main chain can be obtained by enantiomer-selective pol5nnerization (lUPAC nomenclature asymmetric enantiomer-differentiating polymerization). In enantiomer-selective polymerization, one antipode of a racemic chiral monomer is preferentially polymerized to afibrd an optically active polymer. In this process, kinetic resolution of the racemic monomer takes place. The first clear polymerization of this typ>e was reported for propylene oxide. 

Thus polymers can be classified according to their configurations or tacticity. In this nomenclature, they are either isotactic, atactic or syndiotactic. 

About the nomenclature of like and unlike The meso and racemo nomenclature commonly used for vinyl monomer diads, are not applicable to the head-to-tail polyketone because the junchon unit between the two stereocenters, -CH2-C(=0)-, is not symmetric. Poly(a-amino acid)s and poly(propylene oxide) are other examples of polymers with asymmetric (W. V. Metanomski, Compendium of Macromolecular Nomenclature, lUPAC Macromolecular division). Accordingly, the words like and unlike, which are used in organic chemistry, are applied like (/) is used for the diad consisting of the same configuration (analogous to meso) and unlike ( ) for the opposite (analogous to racemo). 

The nomenclature of polymer configurations reported in the chapter are based on the lUPAC reports ... 

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