Conformation of Azobenzene-Modified Poly(α-L-Glutamate) (AZOPLGA) in Thin Films: Solid State NMR Studies

• Published in: Journal of macromolecular science. Part A, Pure and applied chemistry Vol. 41; no. 12; pp. 1359 - 1368
• Main Authors: Wu, Xiaodong, Yang, Suizhou, Samuelson, Lynne A., Cholli, Ashok L., Kumar, Jayant
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Colchester Taylor & Francis Group 31-12-2004; Taylor & Francis
• Subjects: Applied sciences; Azobenzene-modified PLGA; Cast thin film; Conformation; Exact sciences and technology; Inorganic and organomineral polymers; Physicochemistry of polymers; Properties and characterization; Solid state NMR; Solvent effect; Glutamic acid copolymer; Solid state NMR; Aminoacid copolymer; Composition effect; Cast thin film; Experimental study; Lateral group; Thin film; Azo compound; Solid state; Light sensitive copolymer; Azobenzene-modified PLGA; Fabrication structure relation; Conformation; Glutamic acid derivative copolymer
• ISSN: 1060-1325; 1520-5738
• DOI: 10.1081/MA-200035277

The conformations of azobenzene-modified poly(α-L-glutamate)s (AZOPLGA) with a different degree of functionalization were examined by solid state
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C NMR. The polymer main chain conformations in AZOPLGA powders (precipitated from reaction system) changes from α-helix to β-sheet when the degree of functionalization increases from 12% to 56%. In addition, the solvent used for fabricating films plays an important role in organizing AZOPLGA backbones into characteristic conformation. For AZOPLGA56 (AZOPLGA with 56% of functionalization) cast films, the polymer backbones can assume conformations ranging from order state (β-sheet) to random coil by changing the solvent for fabrication. In contrast, the effect of solvent on the conformation of AZOPLGA23 (AZOPLGA with 23% of functionalization) is not so significant. When compared with AZOPLGA23 powder (precipitated from reaction system), the helical conformation increases for AZOPLGA23 film cast from TFA. However, the fractions of α-helix and β-sheet conformation in AZOPLGA23 films (cast from DMF or pyridine) are nearly identical to that of AZOPLGA23 power. Moreover, even though the polymer backbones are random coil in AZOPLGA56 films when cast from TFA, some locally ordered domain can be observed. Lastly, the effect of the azo content appears to play a dominant role over the effect of solvents in directing the conformation of these polymers.
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Dedicated to the Memory of Professor Sukant K. Tripathy.