02715nas a2200253   4500008004100000022001400041245012000055210006900175260006800244300001400312490000700326520180900333653001302142653002802155653002502183653001002208653001902218653001802237653001902255100001702274700002802291700001602319856012602335       2005                        eng d  a0887-624X00aStructure of poly(L-lactic acid)s prepared by the dehydropolycondensation of L-lactic acid with organotin catalysts0 aStructure of polyLlactic acids prepared by the dehydropolyconden  a111 RIVER ST, HOBOKEN, NJ 07030 USAbJOHN WILEY & SONS INCcMAY  a2164-21770 v433 a<p>The synthesis of low-molecular-weight (weight-average molecular weight &lt; 45,000 g/mol) lactic acid polymers through the dehydropolycondensation of L-lactic acid was investigated. Polymerizations were carried out in solution with solvents (xylene, mesitylene, and decalin), without a solvent using different Lewis acid catalysts (tetraphenyl tin and tetra-n-butyldichlorodistannoxane), and at three different polymerization temperatures (143, 165, and 190 degrees C). The products were characterized with differential scanning calorimetry, size exclusion chromatography, vapor pressure osmometry, C-13 NMR, and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF). The resulting polymers contained less than 1 mol % lactide, as shown by NMR. The number-average molecular weights were calculated from the ratio of the area peaks of ester carbonyl and carboxylic acid end groups via C-13 NMR. The stereosequences were analyzed by C-13 NMR spectroscopy on the basis of triad effects. Tetraphenyl tin was an effective transesterification catalyst, and the randomization of the stereosequence at 190 degrees C was observed. In contrast, the distannoxane catalyst caused comparatively less transesterification reaction, and the randomization of the stereosequences was slow even at 190 degrees C. The L-lactic acid and D-lactic acid isomers were added to the polymer chain in a small, blocky fashion. The MALDI-TOF spectra of poly(L-lactic acid) (PLA) chains doped with Na+ and K+ cations showed that the PLA chains had the expected end groups. The MALDI-TOF analysis also enabled the simultaneous detection of the cyclic oligomers of PLA present in these samples, and this led to the full structural characterization of the molecular species in PIA. (c) 2005 Wiley Periodicals, Inc.</p>10aC-13 NMR10adehydropolycondensation10aLewis acid catalysts10aMALDI10apolymerization10arandomization10astereosequence1 aShyamroy, S.1 aGarnaik, Baijayantimala1 aSivaram, S.  uhttp://library.ncl.res.in/content/structure-polyl-lactic-acids-prepared-dehydropolycondensation-l-lactic-acid-organotin-001330nas a2200169   4500008004100000022001400041245016100055210006900216260005700285300001200342490000700354520061000361100001700971700002800988700001601016856012801032       2015                        eng d  a0170-083900aHigh molecular weight polylactic acids by polyesterification using diisopropylcarbodiimide (DIPC) and 4-(dimethylamino) pyridinium ptoluene sulfonate (DPTS)0 aHigh molecular weight polylactic acids by polyesterification usi  a233 SPRING ST, NEW YORK, NY 10013 USAbSPRINGERcMAR  a405-4150 v723 a<p>High molecular weight poly(l-lactic acid) has been prepared from the corresponding functionally terminated oligomers employing a polyesterification method at room temperature using diisopropylcarbodiimide and 4-(dimethylamino) pyridinium-p-toluene sulfonate. Self-condensation of hydroxyl and carboxylic acid-terminated poly(l-lactic acid) oligomers (M (n) : similar to 1,000) resulted in polymers with high molecular weights (M (n) &gt; 45,000) under mild conditions. End-group analysis by MALDI-TOF provided evidence for N-acylurea formation in the product under the reaction conditions employed.</p>1 aShyamroy, S.1 aGarnaik, Baijayantimala1 aSivaram, S.  uhttp://library.ncl.res.in/content/high-molecular-weight-polylactic-acids-polyesterification-using-diisopropylcarbodiimide-0