Stereoisomerism in polymers

Detailed discussion of polymer tacticity can be found in texts by Randall,2 Bovey,1-3 Koenig,4-5 Tonelli6 and Hatada.7 In order to understand stereoisomerism in polymer chains formed from mono- or 1,1-disubstiluted monomers, consider four idealized chain structures ... 

The occurrence of stereoisomerism in polymers plays a major role in their practical utilization. There are very significant differences in the properties of unordered and ordered polymers as well as in the properties of ordered polymers of different types (cis versus trans, isotactic versus syndiotactic). The ordered polymers are dramactically different from the corresponding unordered structures in morphological and physical properties. 

Infrared spectroscopy has been used for quantitatively measuring the amounts of 1,2-, 3,4-, cis-1,4-, and trans-1,4-polymers in the polymerization of 1,3-dienes its use for analysis of isotactic and syndiotactic polymer structures is very limited [Coleman et al., 1978 Tosi and Ciampelli, 1973]. Nuclear magnetic resonance spectroscopy is the most powerful tool for detecting both types of stereoisomerism in polymers. High-resolution proton NMR and especially 13C NMR allow one to obtain considerable detail about the sequence distribution of stereoisomeric units within the polymer chain [Bovey, 1972, 1982 Bovey and Mirau, 1996 Tonelli, 1989 Zambelli and Gatti, 1978],... 

A general and precise description of stereoisomerism in polymers is suggested on the basis of the repetition theory which describes the distinct patterns along a line that can be obtained from a three-dimensional motif. The probability models for describing the" stero-sequence length in various possible cases of interest in stereoregular polymers are discussed. It is shown that for describing the stereosequence structure, the simplest probability model must involve a Markov chain with four probability parameters. 

Classifying Stereoisomerism in Polymers on the Basis of Repetition of a Three-Dimensional Motif... 

Nuclear magnetic resonance has been extensively used to investigate stereoisomerism in polymers such as polypropylene, polyacrylates, vinyl polymers. 

Optical Activity in Polymers Stereoisomerism in polymers is formally similar to the optical isomerism of organic chemistry. In a vinyl polymer with the general structure shown in (XIH) every other carbon atom in the chain, labeled C, is a site of steric isomerism, because it has four different substituents, namely, X, Y, and two sections of the main chain that differ in length (Rudin, 1982). 

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