Sandrine Pensec

Self-assembly of liquid crystal block copolymer PEG-b-smectic polymer in pure state and in dilute aqueous solution.

A series of amphiphilic LC block copolymers, in which the hydrophobic block is a smectic polymer poly(4-methoxyphenyl 4-(6-acryloyloxy-hexyloxy)-benzoate) (PA6esterl) and the hydrophilic block is polyethyleneglycol (PEG), were synthesized and characterized. The self-assembly of one of them in both the pure state and the dilute aqueous solution was investigated in detail. Nano-structures in the pure state were studied by SAXS and WAXS on samples aligned by a magnetic field. A hexagonal cylindrical micro-segregation phase was observed with a lattice distance of 11.2 nm. The PEG blocks are in the cylinder, while the smectic polymer blocks form a matrix with layer spacing 2.4 nm and layer normal parallel to the long axis of the cylinders. Faceted unilamellar polymer vesicles, polymersomes, were formed in water, as revealed by cryo-TEM. In the lyotropic bilayer membrane of these polymersomes, the thermotropic smectic order in the hydrophobic block is clearly visible with layer normal parallel to the membrane surface.

Anionic polymerization of d,l-lactide initiated by lithium diisopropylamide

The anionic polymerization of d,l-lactide initiated by lithium diisopropylamide.monoTHF complex was performed in different solvents and at various temperatures. No polymerization took place in THF solution. In dioxane at 25°C the polymerization is fast and goes up to completion in few minutes. In toluene, due to solubility requirements, polymerizations were run at 70°C. At initial stage of polymerization Mw/Mns were quite narrow, but at higher conversion a significant broadening occurred due to transesterification reactions. The latter were identified by 13C NMR analysis, while MALDI-TOF spectra revealed the simultaneous presence of cyclic and linear oligomers substantiating the occurrence of both intra and inter ester exchange processes. At low conversion, polymers exhibited a highly syndiotactic microstructure.

New hybrid core–shell star-like architectures made of poly(n-butyl acrylate) grown from well-defined titanium oxo-clusters

New hybrid star-like macromolecular objects have been designed from an inorganic multifunctional platform following two routes. The first one consists of the direct introduction of polymer arms at the surface of the titanium oxo-cluster [Ti16O16(OEt)32] by alkoxide exchange. The second approach corresponds to the growth by Atom Transfer Radical Polymerization (ATRP) of n-butyl acrylate from the macroinitiator [Ti16O16(OEt)26(OCH2CCl3)6]. By crossing different characterization techniques and methodologies (single crystal X-ray diffraction, 13C and 17O NMR and 1H DOSY NMR spectroscopy, Size Exclusion Chromatography), evidence of the formation of such macromolecular compounds is reported.

Supramolecular design for polymer/titanium oxo-cluster hybrids: an open door to new organic–inorganic dynamers

Hybrid materials from organic polymers and inorganic solids often possess enhanced properties compared to their isolated constituents, if intimate mixing is achieved. We report a new approach combining inorganic nanobuilding blocks and supramolecular interactions, exemplified by a titanium oxo-cluster bearing four hydrogen bond acceptors and a telechelic PDMS with two hydrogen bond donors. With these simple components, we demonstrate that well chosen supramolecular interactions can be used to obtain new hybrid dynamers having the intrinsic properties of the inorganic component (such as photochromism) and improved mechanical properties, due to the supramolecular cross-linking of the polymer chains.

Patchy Supramolecular Bottle-Brushes Formed by Solution Self-Assembly of Bis(urea)s and Tris(urea)s Decorated by Two Incompatible Polymer Arms

In an attempt to design urea-based Janus nanocylinders through a supramolecular approach, nonsymmetrical bis(urea)s and tris(urea)s decorated by two incompatible polymer arms, namely, poly(styrene) (PS) and poly(isobutylene) (PIB), were synthesized using rather straightforward organic and polymer chemistry techniques. Light scattering experiments revealed that these molecules self-assembled in cyclohexane by cooperative hydrogen bonds. The extent of self-assembly was limited for the bis(urea)s. On the contrary, reasonably anisotropic 1D structures (small nanocylinders) could be obtained with the tris(urea)s (Nagg ∼ 50) which developed six cooperative hydrogen bonds per molecule. (1)H transverse relaxation measurements and NOESY NMR experiments in cyclohexane revealed that perfect Janus nanocylinders with one face consisting of only PS and the other of PIB were not obtained. Nevertheless, phase segregation between the PS and PIB chains occurred to a large extent, resulting in patchy cylinders containing well separated domains of PIB and PS chains. Reasons for this behavior were proposed, paving the way to improve the proposed strategy toward true urea-based supramolecular Janus nanocylinders.

An ω-functionalized perfluoroalkyl chain: synthesis and usein liquid crystal design

A multiblock polyphilic compound incorporating a perfluoroalkyl spacer nand associating groups at both extremities exhibits smectic A and smectic nC mesophases.