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Direct condensation of d,l- and l-lactic acids: effect of AlCl3 catalyst on microstructural arrangements of homopolymers and copolymers

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The effect of AlCl3 as a catalyst in direct condensation of homopolymerization and copolymerization of (rac and l)-lactic acid was studied. The morphological effect of dimer formation via racemization during polymerization with respect to time and catalyst concentration was investigated at 180°C under vacuum conditions (176 mmHg). The sequence distribution of triads and hexads was analyzed using 13C NMR spectroscopy. A combination of Avrami and Ozawa equations for mathematical modelling of the non-isothermal crystallization kinetics of the synthesized poly(d,l-lactic acid) produced consistent results with the experimental data under these conditions. It is shown that AlCl3 promotes racemization which leads to formation of ill-defined polymers, as demonstrated by determinations of molecular weight distribution (Mn < 5279 g/mol, PDI = 1.4-3), optical purity (91.67% - 99.36%) and melting temperature (143-155°C). The activation energy for crystal growth during the cooling of molten samples of poly(d,l-lactic acid), as determined by Kissinger method, is found to be 45 kcal per mol. In this respect, the microstructural effect of copolymers on their thermal behaviour is discussed.
Original languageEnglish
Pages (from-to)523-533
Number of pages11
JournalIranian Polymer Journal
Volume20
Issue number6
Publication statusPublished - 2011

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