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Inter‐ and intramolecular ester exchange reactions in the ring‐opening polymerization of ( D , L )‐lactide using lanthanide alkoxide initiators
Author(s) -
Spassky Nicolas,
Simic Vesna,
Montaudo Maurizio S.,
HubertPfalzgraf Liliane G.
Publication year - 2000
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(20001101)201:17<2432::aid-macp2432>3.0.co;2-i
Subject(s) - alkoxide , polymerization , chemistry , polymer chemistry , ring opening polymerization , transesterification , tacticity , lanthanide , polymer , organic chemistry , catalysis , ion
Polylactide samples obtained by the ring‐opening polymerization of ( D , L )‐lactide by using different lanthanide alkoxide initiators were examined by SEC, 13 C NMR and MALDI‐TOF MS techniques. The evidence of substantial transesterification was observed in the case of a polymerization initiated by lanthanum alkoxide and bimetallic aluminium‐yttrium alkoxide initiators. In the case of Y and Sm alkoxide initiators, the MWD remains narrow up to high conversions for reasonable polymerization times, but the prolongation of the post ‐polymerization time increases the amount of ester‐exchange reactions. The extent of the transesterification reactions was evaluated on the basis of the intensity of the stereosequence resonances for the methine carbon signal in the 13 C NMR spectra. MALDI‐TOF MS analysis revealed the presence of odd‐membered oligomers in all spectra. Thus, transesterification reactions occur from the beginning of the polymerization. Linear and cyclic oligomers were detected in some cases indicating the simultaneous occurrence of inter‐ and intramolecular exchange reactions. The microstructure analysis of the polymers by 13 C NMR spectroscopy indicates a preference for a syndiotactic addition during the polymerization process.