Inclusion complexes of α-cyclodextrins with poly(d,l-lactic acid): structural, characterization, and glass transition dynamics
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Poly (d,l-lactic acid) (PDLLA) was combined with α-CD to form inclusion complexes (ICs) with distinct PDLLA fractions. The structural changes resulting from this coalescence process were analyzed by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), and X-ray diffraction (XRD). The presence of both components in the ICs was confirmed by FTIR. The encapsulated PDLLA fraction was quantified by 1H NMR. XRD data evidenced that it was possible to transform the amorphous PDLLA into a well-organized channel-type crystalline structure. DSC showed that the glass transition temperature of the PDLLA fraction in the ICs was higher than in the pure polymer, indicating that the ultra-confinement effect imposed by the ICs organization clearly limits PDLLA molecular dynamics. The confinement effect on the glass transition dynamics was investigated by unconventional dynamic mechanical analysis experiments, which confirmed that ICs segmental mobility is highly restricted when compared with the one of pure PDLLA. Bulk PDLLA presents a typical VFTH behavior while the ICs dynamics shows an Arrhenius trend.
KeywordsPoly(d,l-lactic acid) Inclusion complexes Glass transition dynamics
Portuguese Foundation for Science and Technology (FCT) for financial support through the PTDC/FIS/115048/2009 project and to the NMR Portuguese network (PTNMR, Bruker Avance III 400-Univ. Minho). FCT and FEDER (European Fund for Regional Development)-COMPETE-QREN-EU for financial support to the Research Centre, CQ/UM [PEst-C/QUI/UI0686/2011 (FCOMP-01-0124-FEDER-022716)].
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