Analysis of Stereoregularity

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], 

Consider the description of the sequence distribution of isotactic and syndiotactic placements in the polymerization of a monosubstituted ethylene. The approach is general and can be applied with appropriate modification to the 1,4-polymerization of a 1,3-diene. Dyad tac-ticity is defined as the fractions of pairs of adjacent repeating units that are isotactic or syndiotactic to one another. The isotactic and syndiotactic dyads (XV) are usually referred to as meso and racemic dyads. The horizontal line in XV represents a segment of the polymer 

These definitions are clarified by considering a portion of a polymer chain such as XVII. Chain segment XVII has a total of 9 repeating units but only 8 dyads and 7 triads. There are 6 meso dyads and 2 racemic dyads (m) —, (r) —, There are 4 isotactic, 2 heterotactic, and 1 syndiotactic triads mm) = (mr) — j, (rr) — A. 

The dyad and triad fractions each total unity by definition, that is 

The advent of high-resolution 13 C NMR allows the determination of tetrad, pentad, and even higher sequence distributions in many polymers [Bovey, 1972 Bovey and Mirau, 1996 Farina, 1987]. The tetrad distribution consists of the isotactic sequence mmm, the syndiotactic sequence rrr, and the heterotactic sequences mmr, rmr, mrm, rrm. The sum of the tetrad fractions is unity, and the following relationships exist  

These definitions are clarified by considering a portion of a polymer chain such as XVII. Chain segment XVII has a total of 9 repeating units but only 8 dyads and 7 triads. There are 

6 meso dyads and 2 racemic dyads (m) — (r) = There are 4 isotactic, 2 heterotactic, and 

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Cho D, Park S, Chang T, Ute K, Fukuda 1, Kitayama T. Temperature gradient interaction chromatography and MALDl-TOF mass spectrometry analysis of stereoregular poly(ethyl methacrylatejs. Anal Chem 2002 74 1928. 

PRESENT STATUS OF THE CONFIGURATIONAL AND CONFORMATIONAL ANALYSIS OF STEREOREGULAR POLYMERS... 

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