Molecular weight-based fractionation of poly-l- and poly-d,l-lactic acid polymers via a simple inclusion compound based process

Abstract

Urea inclusion compound (UIC) formation was used to fractionate carbohydrate polymers, poly-l- and poly-dl-lactic acid, by molecular weight. The UIC fractionation process employed was rapid, simple, scalable, and may have potential for use in preparative- and large-scale purification of polymers. Differential scanning calorimetry measurements reflect the formation of UICs for both polymer types. Under the conditions employed, the resultant UIC-rich solid phase contained polylactic acids of molecular weight distribution similar to the process feed sample, whereas the solvent-rich phase contained polymer of significantly lower molecular weight. The difference in molecular weight increased with the average molecular weight of the polymer and the degree of incorporation of polymer in the solid phase, and was greater for poly-d,l- than poly-l-lactic acid. The distribution of urea between the solid and the solvent-rich phases was independent of the molecular weight of the polymer or stereochemistry for a given polymer–urea–solvent ratio in the mixture.

Keywords:

• Extraction
• Polymer fractionation
• Poly(lactic acid) fractionation
• Urea inclusion compounds

Acknowledgments

Ms. Britni Newton and Ms. Opey Moyegun are acknowledged gratefully for assisting in the collection of GPC data. We also thank Mr. Mart Eenink (Purac) and Dr. John Middleton (Birmingham Polymers) for their technical assistance and their kind donation of samples. Financial support for this work came from the Swedish NUTEK and NFR organizations, as well as the American NSF-EPSCOR program. We thank Dr. Jimmy W. Mays (Department of Chemistry, University of Alabama–Birmingham) for kindly making his DSC facilities available for this work, Mr. Jinchuan Yang and Mr. Jason Jimmerson for conducting the DSC analyses, Dr. K. K. Chittur (Department of Chemical and Materials Engineering, University at Alabama–Huntsville) for kindly permitting use of his FTIR facilities, and Mr. Ashish Bezawada for obtaining the FTIR spectra and preparing the KBr films used as FTIR samples.