ROPs of l-lactide catalyzed by neat Tin(II)2-ethylhexanoate - Influence of the reaction conditions on Tm and ΔHm

l-Lactide was polymerized by means of neat SnOct2 with variation of LA/Cat ratio, temperature and time. The resulting cyclic polylactides crystallized spontaneously at 160 °C or below, but needed nucleation via mechanical stress at 165 or 170 °C. All the crystalline polylactides obtained directly fr...

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Bibliographic Details
Published inPolymer (Guilford) Vol. 231; p. 124122
Main Authors Meyer, Andreas, Weidner, Steffen M., Kricheldorf, Hans R.
Format Journal Article
LanguageEnglish
Published Kidlington Elsevier Ltd 28.09.2021
Elsevier BV
Subjects
Annealing
Catalysts
Crystallites
Crystallization
Crystals
Lactide
Nucleation
Polylactic acid
Ring-opening polymerization
SAXS
Transesterification
Ring-opening polymerization
Transesterification
Lactide
Crystallization
SAXS
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Summary:l-Lactide was polymerized by means of neat SnOct2 with variation of LA/Cat ratio, temperature and time. The resulting cyclic polylactides crystallized spontaneously at 160 °C or below, but needed nucleation via mechanical stress at 165 or 170 °C. All the crystalline polylactides obtained directly from ROP above 120 °C had melting temperatures (Tm) above 189 °C (up to 194.5 °C). SnOct2 also enabled transformation of low Tm poly(l-lactide)s (Tm < 180 °C) into the high Tm m1odification by annealing, due to the impact of transesterification reactions in the interphase between the crystallites. The influence of crystallization temperature and annealing time on the crystal thickness was studied via SAXS measurements. A comparison with the crystallization and annealing experiments reported by Pennings and coworkers and Tsuji and Ikada is discussed, and a satisfactory agreement has been found, because those authors also studied polyLA samples containing SnOct2 in its active form. It is also demonstrated in this work that the high Tm modification cannot be obtained when the catalyst is removed or poisoned as it is true for commercial polylactides. [Display omitted] •The most stable morphology of poly(l-lactide) with a maximum Tm was achieved.•Evidence for SnOct2-catalyzed transesterification in the solid state is presented.•Discrepancies between literature data are explained.
ISSN:0032-3861
1873-2291
DOI:10.1016/j.polymer.2021.124122