Solid State 13C CP-MAS NMR Studies of the Crystallinity and Morphology of Poly(l-lactide)

Biodegradable polyesters as crystallization-accelerating agents of poly(l-lactide)

A series of biodegradable polyesters, poly[(R)-3-hydroxybutyrate] (PHB), poly(-caprolactone) (PCL), and polyglycolide (PGA), were found to be effective crystallization-accelerating agents for poly(l-lactide) (PLLA). Differential scanning calorimetry and polarized optical microscopy strongly suggested that the accelerated crystallization of PLLA in the presence of the three biodegradable polyesters is attributable to a nucleation-assisting effect of PCL and PGA and a spherulite growth-accelerating effect of PHB, although the incorporated PHB lowered the spherulite number of PLLA per unit area. The spherulite growth-accelerating effect of PHB probably resulted from the relatively high miscibility of PLLA with PHB and the low glass transition temperature of PHB compared to that of PLLA. The crystallization kinetics of PLLA varied only in the case of PLLA/PHB blends during cooling from the melt, as evidenced by the nucleation constant and radius growth rate values of the spherulites. The nucleation and growth types of PLLA crystallites are thought to be altered only in the case of PLLA/PGA blends during heating, as evidenced by Avrami exponent n values.

Kinetics of solid-state NMR cross-polarization from protons to carbon-13 in surgical sutures

Commercial Dexon surgical sutures, made of polyglycolide (PGA), were examined using (13)C CP/MAS NMR. The study shows that detailed analysis of the cross-polarization (CP) process is useful in the peak assignments and in the assessment of molecular mobility in the polymer domains. Crystallinity of PGA in the sutures was estimated at ca. 55%.

Applications of high-resolution solid-state NMR spectroscopy in food science

The principal applications of high-resolution solid-state NMR spectroscopy, in the field of food science, are reviewed, after a short general introduction, mainly focusing on the potential of these investigations, which are, today, routine tools for resolving technological problems. Selected examples of the applications in the field of food science of high-resolution solid-state NMR spectroscopy both in (13)C and in (1)H NMR particularly illustrative of the results obtainable are reported in some detail.

Real-time imaging of crystallization in polylactide enantiomeric monolayers at the air-water interface

A newly developed planar array infrared reflection-absorption spectrograph (PA-IRRAS) offers significant advantages over conventional approaches including fast acquisition speed, excellent compensation for water vapor, and an excellent capacity for large infrared accessories, e.g., a water trough. In this study, the origin of stereocomplexation in a polylactide enantiomeric monolayer at the air-water interface was investigated using PA-IRRAS. PA-IRRAS was used as a probe to follow the real-time conformational changes associated with intermolecular interactions of polymer chains during the compression of the monolayers. It was found that a mixture of poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) (D/L) formed a stereocomplex when the two-dimensional monolayer developed at the air-water interface before film compression, indicating that there is no direct correlation between film compression and stereocomplexation. PA-IRRAS spectra of the stereocomplex exhibited distinct band shifts in crystalline sensitive components, e.g., the vas(C-O-C, h) mode, as well as amorphous-dependent components, e.g., the vs(C-O-C) mode, when compared with the spectra of PLLA alone. On the other hand, time-resolved PA-IRRAS spectra, which were obtained as the films were being compressed, revealed that both monolayers of PLLA and mixed PLLA/PDLA stereocomplex were crystallized into a 10(3)-helix and a 3(1)-helix, respectively, with a distinct band shift in crystalline sensitive components only. Fourier self-deconvolution of the spectra demonstrated that the band shift in crystalline sensitive components is correlated with the intermolecular interaction of polymer chains.

Molecular dynamics of poly(L-lactide) biopolymer studied by wide-line solid-state 1H and 2H NMR spectroscopy

The molecular dynamics of poly(L-lactide) (PLLA) biopolymer was characterized through analyses of 1H and 2H NMR line-shapes and spin-lattice relaxation times at different temperatures. At low temperatures (e.g. 90 K), the methyl group rotation is dominant leading to a significant reduction in the proton second moment. Fast methyl group reorientation occurs at ca. 130 K. In additional to the fast methyl group rotation, hydroxyl groups start to reorient as the temperature increases further, eventually leading to the breakdown of the segments of the biopolymer chains above its glass transition temperature Tg of 323 K. The analyses of the 2H NMR line-shapes indicate that both the methyl and hydroxyl reorientations can be described by the so-called cone model, in which the former has three equilibrium positions with theta(C-D) = 70.5 degrees and phi = 120 degrees while the latter one exhibits two equilibrium positions with theta(O-D) = 78 degrees and phi = 180 degrees .