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1H and 13C NMR analyses of l- and d.l-lactic acid oligomers were found considerably improved by recording spectra in DMSO-d 6 instead of CDCl3. Systematic comparison of oligomer spectra led to the identification of a neighboring effect which was shown to be linearly additive. Assignment of all the 13C NMR chemical shifts belonging to the different constitutive units was realized up to the octamer. Furthermore, the well-identified positions of the resonances of chain end units in the 1H NMR spectra were used to determine the absolute average degree of polymerization of oligomers issued from polycondensation. Data were also used to study oligomers with covalently modified chain ends. Findings are of great interest for the study of the ultimate degradation stages of poly(lactic acid)s.

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PLA/PEO/PLA triblock copolymers bearing short poly(l-lactic acid) blocks, with the number average degree of polymerization of each PLA block PLA = 2, 4, 8, and 12, were synthesized by ring opening polymerization of l-lactide initiated by poly(ethylene glycol) in the presence of CaH2. The length of PEO blocks was varied by using parent PEG of different number average degrees of polymerization PEG = 14, 26, and 49, respectively, according to SEC and NMR. SEC and 1H and 13C NMR showed the resulting triblock copolymers did not contain any detectable PLA homopolymer as side product. The use of DMSO-d 6 as solvent for NMR analyses, instead of CDCl3, greatly enhanced the resolution and permitted the distinction of the signals due to the last two constitutive units located at both ends of each PLA block. Data obtained by FTIR spectroscopy and X-ray diffractometry suggested that PEO and PLA blocks were phase separated even for copolymers with very short PLA blocks. Optical microscopy and DSC showed that an increase in the length of PLA blocks led to a decrease in the crystallinity of PEO blocks up to disappearance. Hydrolysis was carried out in DMSO/D2O in the presence of trifluoroacetic acid and monitored by NMR. Data suggested that intrachain and PEO/PLA connecting ester bonds were cleaved at comparable rates in the selected homogeneous medium.

A series of triblock PLA/PEO/PLA copolymers were synthesized by polymerization of l-lactide in the presence of PEG2000, a bifunctional OH-terminated poly(ethylene glycol) (M̄ n = 1800) using Zn metal or CaH2 as catalyst. The resulting copolymers were analyzed by various techniques including 1H and 13C nuclear magnetic resonance, size-exclusion chromatography, X-ray diffractometry, optical microscopy, and differential scanning calorimetry. NMR spectra showed that Zn and CaH2 catalyzed lactide polymerization under the selected experimental conditions to yield long PLA blocks at both ends of the PEG macroinitiator. The copolymer composition was comparable to that of the feed even after purification by dissolution/precipitation. Hydrolysis of the triblock copolymers conclusively showed that the early stages of ester bond cleavage proceeded at random along the PLA blocks. As degradation advanced, a highly swollen hydrogel layer expanded from the surface of a still compact, partially degraded specimen. According to NMR analysis, this layer was composed of PLA/PEO/PLA copolymers bearing short PLA blocks which resulted from the degradation of parent long blocks. It remained attached to the surface via physical interactions within hydrophobic microdomains composed of clustered PLA segments.

Continuous defect-free nanofibers containing chitosan (Ch) or quaternized chitosan (QCh) were successfully prepared by one-step electrospinning of Ch or QCh solutions mixed with poly[(L-lactide)-co-(D,L-lactide)] in common solvent. XPS revealed the surface chemical composition of the bicomponent electrospun mats. Crosslinked Ch- and QCh-containing nanofibers exhibited higher kill rates against bacteria S. aureus and E. coli than the corresponding solvent-cast films. SEM observations showed that hybrid mats were very effective in suppressing the adhesion of pathogenic bacteria S. aureus. The hybrid nanofibers are promising for wound-healing applications.

Novel polyelectrolyte complexes (PECs) between N-carboxyethylchitosan (CECh) and well-defined (quaternized) poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) have been obtained. The modification of chitosan into CECh allows the preparation of PECs in a pH range in which chitosan cannot form complexes. The CECh/PDMAEMA complex is formed in a narrow pH range around 7. The quaternization of the tertiary amino groups of PDMAEMA enables complex formation with CECh both in neutral and in alkaline medium. Cross-linked CECh is also capable of forming complexes with (quaternized) PDMAEMA. The antibacterial activity of (cross-linked) CECh, (quaternized) PDMAEMA, and their complexes against Escherichia coli has been evaluated. In contrast to (quaternized) PDMAEMA, (cross-linked) CECh exhibits no antibacterial activity. The complex formation between cross-linked CECh and (quaternized) PDMAEMA results in a loss of the inherent antibacterial activity of the latter in neutral medium. In acidic medium, the complexes exhibit strong antibacterial activity due to complex disintegration and release of (quaternized) PDMAEMA.

The first successful preparation of chitosan-containing nanofibres was achieved by electrospinning of chitosan/poly(ethylene oxide) (PEO) blend aqueous solutions. The diameters of the nanofibres were in the range 40 -290 nm and decreased with increasing chitosan content and decreasing total concentration. An increase of the applied field strength leads to an increase of the diameter of the nanofibres and to a broadening of the size distribution. The possibility to prepare nanofibres containing a model drug -potassium 5-nitro-8-quinolinolate (K5N8Q), a broad-spectrum antimicrobial and antimycotic agent -was shown. The incorporation of K5N8Q in the nanofibres resulted in a decrease of the nanofibre diameters and the appearance of bead-shaped defects. Non-woven mats from the drugloaded nanofibres with composition chitosan : PEO = 1:1 (w/w) and 1% K5N8Q showed antibacterial and antimycotic activity against E. coli, S. aureus and C. albicans.