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Stereospecific Polymerization of Methylthiirane in Homogeneous Phase, 6. 13 C NMR Study of the Stereocontrol Mechanism: An Access to the Size of Stereoblocks
Author(s) -
Boucard V.,
Moreau M.,
Dumas Ph.
Publication year - 2001
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/1521-3935(20010601)202:9<1974::aid-macp1974>3.0.co;2-2
Subject(s) - diad , triad (sociology) , polymerization , chemistry , stereospecificity , carbon 13 nmr , tacticity , polymer chemistry , catalysis , nmr spectra database , polymer , stereochemistry , spectral line , organic chemistry , copolymer , physics , psychology , psychoanalysis , astronomy
The polymerization of methylthiirane initiated by bis(isopropyl‐( S )‐cysteinato)cadmium is stereospecific and enantioasymmetric and occurs through a catalyst site control. Until now, the mechanism of polymerization could not be verified by NMR because the too low resolution of the spectra showed only a diad effect. 13 C NMR at 125.76 MHz shows triad effects that permit the examination of the polymerization mechanism. Experimental triad contents do not fit either with the values calculated from the expected catalyst site control (Bernoullian statistics) or from a growing chain‐end control (Markov 1 st order statistics). This can be explained by the interconversion between active sites occurring in this homogeneous system. These interconversions lead to the formation of stereoblocks the length of which have been estimated by comparing experimental NMR results with those calculated from catalyst site control. We found about 38 interconversions for the studied polymer corresponding to DP n of stereoblocks of around 12–14.