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The Role of Transesterification in SnOct 2 ‐Catalyzed Polymerizations of Lactides
Author(s) -
Weidner Steffen M.,
Kricheldorf Hans R.
Publication year - 2017
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/macp.201600331
Subject(s) - transesterification , dispersity , polymerization , lactide , polymer chemistry , monomer , yield (engineering) , catalysis , crystallization , chemistry , molar mass distribution , ring opening polymerization , materials science , organic chemistry , polymer , metallurgy
l ‐lactide or meso‐lactide are polymerized either at 120 °C where the polymerization process of l ‐lactide is accompanied by crystallization, or at 180 °C where poly( l ‐lactide) remains in the molten state. Polymerizations at 120 °C initially yield even‐numbered chains (with respect to lactic acid units) having relatively low dispersity, but the fraction of odd‐numbered chains increases with time and the entire molecular weight distribution changes. Traces of cyclics are only formed after 7 d. Polymerizations at 180 °C yield equilibrium of even and odd‐numbered chains from the beginning, but at low monomer/initiator ratios and short reaction times (<4 h) cyclics are again not formed. They appear at longer reaction times and entail higher dispersities. The results are discussed in terms of five different transesterification mechanisms.