The CdO stretching band of the R-crystal of PLLA has been investigated. In the R crystals splitting reveals the existence of an ordered arrangement of transition moments in the different sites along the helical chain of PLLA. In the R 0 crystals splitting is not observed denoting a lack of ordered arrangement in transition moments. In the R crystals the band at 1776 cm -1 arises from the A mode, and because of its low intensity, its profile is barely changed by transition dipole coupling (TDC) interactions. The E 1 mode is centered at about 1759 cm -1 , and is strongly split due to TDC interactions (also referred as Davydov or exciton splitting) in the lateral direction, resulting in the broad absorption profile observed below 1776 cm -1 in the CdO stretching region. Five different sites (characterized by the arrangement of transition moments) can be discerned along the PLLA helix in the unit cell, each of them establishing TDC interactions of different strength with the chains in the first layer. The CdO stretching band can be regarded as a continuum of adjacent contributions, from which only the overall envelope is observed. The value obtained for the transition moment suggests that excitonic interactions may occur in a collective mode involving the five distinguishable CdO groups in PLLA, explaining the large splitting observed in the CdO stretching region of crystalline polylactides. Repulsive CdO dipole-dipole interactions have also been found, related to the symmetry of the unit cell.

Nanocomposites of equimolar enantiomeric polylactide blends with multiwall carbon nanotubes (MWCNTs) were prepared by a solvent casting/sonication procedure. The first objective of the study was to investigate the effect of MWCNTs as nucleating agents for the selective crystallization of the polylactide (PLA) stereocomplex to obtain PLA‐based nanocomposites. Transmission Electron Microscopy (TEM) studies revealed large agglomerates and poor distribution of the non‐functionalized MWCNTs within the matrix. To enhance the compatibility between PLA and MWCNTs, pyrene‐end‐functionalized PLLA (py‐end‐PLLA) nanocomposites were prepared because of the ability of the pyrene moieties to interact with the MWCNTs via π−π stacking, and were subsequently blended with poly(d‐lactide) (PDLA) to investigate the possibility of achieving nanocomposites in which the enantiomeric blend crystallizes as stereocomplex. The resulting nanocomposites were characterized by Differential Scanning Calorimetry (DSC), X‐ray Diffraction (XRD), TEM, and Nuclear Magnetic Resonance Spectroscopy (NMR), revealing that MWCNTs were efficient nucleating agents for the overall crystallization of the blends. Interestingly, full stereocomplexation could be achieved with the aid of soft specific thermal treatments. According to these results, the addition of small amounts of MWCNTs combined with a mild thermal treatment might extend the processing window for the preparation of polylactides exclusively crystallized in the stereocomplex form. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4327–4337, 2013

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(2011). Poly(ethylene oxide)-b-poly(l-lactide) Diblock Copolymer/Carbon Nanotube-Based Nanocomposites: LiCl as Supramolecular Structure-Directing Agent. Biomacromolecules, 12 (11),[4086][4087][4088][4089][4090][4091][4092][4093][4094] ABSTRACT: This work relies on the CNT dispersion in either solution or a polymer matrix through the formation of a three component supramolecular system composed of PEO-b-PLLA diblock copolymer, carbon nanotubes (CNTs) and lithium chloride. According to a one-pot procedure in solution, the "self-assembly" concept has demonstrated its efficiency using suspension tests of CNTs.Characterizations of the supramolecular system by photon correlation spectroscopy, raman spectroscopy and molecular dynamics simulations highlight the charge transfer interaction from the CNTs towards the PEO-b-PLLA/LiCl complex. Finally, this concept was successfully extended in bulk (absence of solvent) via melt-processing techniques by dispersing these complexes in a poly(L-Lactide) (PLA) matrix. Electrical conductivity measurements and transmission electron microscopy attested for the remarkable dispersion of CNTs, leading to high-performance PLA-based materials.KEYWORDS: carbon nanotubes, polylactide, poly(ethylene oxide), supramolecular interactions, reactive extrusion, nanocomposites, molecular dynamics simulations Intr oductionOver the last two decades, carbon nanotubes (CNTs) have attracted a special attention to design new nanocomposites due to a unique combination of mechanical, thermal, structural and electrical properties. [1][2][3] In the field of biotechnology, CNTs-based biomaterials have also proved quite versatile with applications as diverse as prosthesis, biomolecular recognition and drug delivery systems. 4 Nonetheless, strong intermolecular π-π interactions between the nanotube walls and their high aspect ratio lead to a bundle-like arrangement, which represents a major drawback for their processability and application. 5 Different strategies aiming at the dispersion of the CNTs in solution or in a polymer matrix have thus been developed. Most of them lie in the non-covalent and covalent functionalizations of CNT surface. 6 However, the supramolecular approach is emerging as a very appealing pathway since it takes advantage of the preservation of the unsaturated conjugated structure. [7][8] This is also supported by a wide range of non-covalent interactions, performed in a reliable and cost-effective manner. For instance, these 3 non-covalently coated CNTs maintain their intrinsic features, namely a robust mechanical behavior, a high electronic conductivity, and their potential biosensing properties.Poly(ethylene oxide) (PEO) belongs to the class of polyethers, exhibiting good solubility in water and organic solvents. As far as their applications are concerned, PEO-containing compounds are used as excipients or as carriers in different biological materials, foods and cosmetics. Moreover, these polymers can develop a specific behavior under varied stimuli such as temperature and salt conce...