Breteler, ten, M.R. - Synthesis and thermal properties of hetero-bifunctional PLA oligomers and their stereocomplexes
M.R. ten Breteler, J. Feijen, P.J. Dijkstra, F. Signori
Reactive & Functional Polymers 2013
Hetero-telechelic, low-molecular-weight polylactides (PLAs) were prepared by the zinc-catalyzed ringopening
polymerization of L-lactide or D-lactide using functional initiators and subsequent reaction with
termination reagents, yielding –OH, –COOH, –NH2 and –SH as functional chain ends. Structural characterization
was performed by molecular weight analysis, NMR spectroscopy and MALDI-TOF mass spectrometry.
The thermal behavior of the species was investigated by DSC, which revealed that the
modification of the hydroxyl terminus lowered the number of lactic acid units within a PLA chain that
can effectively participate in crystallization. Both the Tm and DHm values for these polymers were lower
compared to those of PLAs of comparable chain length with no modification of the hydroxyl end-group. In
stereocomplexes prepared from equimolar amounts of the hetero-telechelic PLLAs and PDLAs, this
suppressive effect on Tm and DHm was also observed. Modification of the hydroxyl ends to produce –
COOH, –NH2 and –SH end groups reduced the stereocomplex Tm values to 10–20 C. The lower limit
for the crystallization of the stereocomplexes was found at a DP of 5.