writer：Xiangying Sun, Linbo Wu
keywords：biodegradable, crystallization, polycondensation
source：期刊
specific source：J Appl Polym Sci 121: 3246–3251, 2011
Issue time：2011年

Crystalline dicarboxylated poly(L-lactic acid)s
(dcPLLAs) with number-average molecular weights (Mn’s) of
103 to 104 g/mol were synthesized via the melt polycondensation
of L-lactic acid (LLA) in the presence of succinic anhydride
(SAD), with tin(II) chloride and toluene-4-sulfonic acid
as binary catalysts. They were characterized by end-group titration,
1H-NMR, differential scanning calorimetry, and
wide-angle X-ray diffraction. The terminal COOH percentage
reached over 98%, and the molecular weight could be controlled
by the molar ratio of LLA to SAD. The thermal behaviors
depended on the molecular weight. The poly(L-lactic
acid)s (PLLAs) crystallized slowly for Mn
2000 but quickly
for Mn  4000. The crystallinity increased from 27 to 40%
when Mn grew from 4000 to 10,000.With comparison to ordinary
PLLA, the dcPLLA had the same crystallization structure
but a slightly lower crystallizability. The glass-transition
temperature was clearly higher than that of amorphous
dcPLLAs. With a controllable molecular weight, high COOH
percentage, and crystallinity, the dcPLLA with Mn  4000
appeared to be a suitable prepolymer for the preparation of
high-molecular-weight crystalline PLLA via chain extension