Separation of Polymers by Molecular Weight through Inclusion Compound Formation with Urea and α-Cyclodextrin Hosts

• Published in: Macromolecules 2000-03, Vol.33 (5), p.1813-1818
• Main Authors: Rusa, Cristian C, Tonelli, Alan E
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma991883l

α-Cyclodextrin (α-CD) and urea (U) hosts were used in order to separate a mixture of poly(ethylene glycols) (PEGs) with two different molecular weights (M w = 600 [PEG600] and M w = 20 000 [PEG20000]) by forming the respective inclusion compounds (ICs). Differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD) have been used to verify the formation and successfully characterize all inclusion compounds. The high melting point of the urea inclusion compound (PEG*-U IC) formed from the solution containing both polymers was the first evidence that urea preferentially included poly(ethylene glycol) with the higher molecular weight. The PEG*-U IC and PEG20000-U IC X-ray diffraction patterns and FTIR spectra were very similar to each other, confirming that urea preferentially complexes PEG20000 in their mutual solution. Since the above-mentioned techniques were not as useful in the case of α-CD ICs, viscosity measurements were made in order to demonstrate the molecular weight selectivity of α-CD host. The efflux time of PEG*-α-CD IC solution was much closer to that of a PEG20000-α-CD IC solution, which suggested that α-CD also included poly(ethylene glycol) having a high molecular weight rather than the low molecular weight PEG600. The efflux time of PEG*-U IC solution is almost identical with that of the PEG20000-U IC solution indicating that urea has better molecular weight selective properties than α-CD.