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Bulk polytransesterification of L ‐lactic acid esters: An alternative route to synthesize poly(lactic acid)
Author(s) -
Marques Dina S.,
Gil M. H.,
Baptista Cristina M. S. G.
Publication year - 2012
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.36825
Subject(s) - lactic acid , oligomer , differential scanning calorimetry , racemization , polymer , size exclusion chromatography , polymer chemistry , polymerization , specific rotation , molar mass distribution , materials science , atmospheric pressure , chemical engineering , chemistry , organic chemistry , enzyme , genetics , physics , bacteria , engineering , biology , thermodynamics , oceanography , geology
The synthesis of poly(lactic acid) (PLA) by bulk polytransesterification of different L ‐lactic acid esters was successfully carried out. The experiments were performed in two steps: a first one at 170°C, maximum temperature, and atmospheric pressure, to obtain a viscous oligomer; and a final step at 180°C and under reduced pressure to improve the byproduct elimination and increase the polymerization degree. The ethyl L ‐lactate polytransesterification in the presence of the binary catalytic system Sb 2 O/Zn(O 2 CCH 3 ) 2 ·2H 2 O allowed achieving the highest average molecular weight, 22,300 g mol −1 . The yellowing of the melt polymer samples was recorded. The resulting materials were subjected to several characterization techniques: the chemical structure of PLA was confirmed by 1 H‐NMR, the molecular weight was determined by size exclusion chromatography, thermal behavior measured by differential scanning calorimetry and racemization extent by specific rotation measurements. A special attention was paid to the polymer optical purity, as it is of major importance to assess its quality and the significance of the synthesis route. To the best of our knowledge, there is no previous report dealing with the synthesis of PLA by bulk polytransesterification. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012