Olivier Coulembier

Functionalized cyclic carbonates: from synthesis and metal-free catalyzed ring-opening polymerization to applications

Aliphatic polycarbonates are often referenced for their interesting applications due to their lower tendency to undergo hydrolysis, lower Tg, and their degradation in renewable resources. Their synthesis is described using a series of metal-free catalysts allowing preparation of well-defined polymers in terms of molecular weights and structures. Additionally, some highlights regarding their biomedical applications such as drug targeting are presented.

Probe‐Based 3‐D Nanolithography Using Self‐Amplified Depolymerization Polymers

Scanning probes are capable of addressing and modifying surface structures on the atomic scale, [ 1 ] a capability that has been exploited to create molecular logic devices. [ 2 ] However, in realworld applications, the production of nanoscale patterns and devices requires substantial throughput capabilities in combination with suffi cient tip endurance to address areas on the order of 0.1–1 mm 2 at high resolution. At a typical pixel pitch of 10 nm, this translates to 10 8 –10 10 pixels being written with a single tip. Therefore a highly sensitive patterning approach that is gentle on the tip would be indispensable. Besides the well-established method of local anodic oxidation, [ 3 – 5 ] recent developments in this direction are the fi eld-induced deposition of materials [ 6 , 7 ] and the tip-induced modifi cation or removal of thermomechanically responsive organic materials. [ 8 – 12 ] In addition, it has been shown that on polymeric substrates the wear on a sliding silicon tip can be virtually eliminated, [ 13 ] which is a prerequisite for high-resolution patterning on technologically viable scales. Other stimuli have been used to structure polymers locally using atomic force microscopy (AFM) tips, e.g., mechanical forces in plowing [ 14 ] and ultrasonic patterning [ 15 ] or electron irradiation using fi eld emission from the tip. [ 16 ] In this paper, we describe the fabrication of twoand threedimensional structures based on the local removal of a resist polymer using heated tips. Previous experiments have shown that suffi cient energy is provided by heated tips to break the chemical bonds of a Diels–Alder material, [ 11 ] which subsequently decomposes into volatile monomer units. However, the overall patterning effi ciency is low. The effi ciency can be dramatically enhanced by using self-amplifi ed depolymerization (SAD) polymers. Here, the breaking of a single bond induces the spontaneous depolymerization of the entire polymer chain, [ 17 , 18 ] a concept that was fi rst demonstrated in the early 80’s as a dry lithography approach. Recently it was discovered that using phthalaldehyde SAD polymers two-dimensional

Controllable Processes for Generating Large Single Crystals of Poly(3‐hexylthiophene)

Sowing the seeds: A simple strategy based on self-seeding allows large single crystals of long regioregular poly(3-hexylthiophene) chains to be grown from solution. When appropriately crystallized, materials differing in their degrees of regioregularity and molecular weights formed monoclinic form II crystals with interdigitated hexyl side groups (see picture).

Hydrogen-Bonding Catalysts Based on Fluorinated Alcohol Derivatives for Living Polymerization†

Recognize this! A hydrogen-bonding motif based on hexafluorinated alcohol derivatives (see picture; O red, F yellow) activates electrophilic substrates. The catalytic activity of the hydrogen-bonded systems was demonstrated for the ring-opening polymerization of a variety of strained heterocycles. Narrowly dispersed polymers with predictable molecular weights were obtained with end-group fidelity.

Amphiphilic poly(D- or L-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) block copolymers: controlled synthesis, characterization, and stereocomplex formation.

Novel well-defined amphiphilic poly(D-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) (PDLA-b-PDMAEMA) and poly(L-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) (PLLA-b-PDMAEMA) copolymers were obtained. The synthesis strategy consisted of a three-step procedure: (i) controlled ring-opening polymerization (ROP) of (D- or L-)lactide initiated by Al(O(i)Pr)(3), followed by (ii) quantitative conversion of the polylactide (PLA) hydroxyl end-groups with bromoisobutyryl bromide and (iii) atom transfer radical polymerization (ATRP) of DMAEMA. The PLA block molecular weight was kept below 5000 g/mol. The macromolecular parameters of the (co)polymers were determined by (1)H NMR spectroscopy and size exclusion chromatography (SEC). The stereocomplexes of PDLA-b-PDMAEMA/PLLA-b-PDMAEMA diblock copolymers were prepared via solvent casting. The stereocomplex formation was evidenced by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. The obtained stereocomplexes had melting temperature of about 65 degrees C above that of the individual copolymers and exhibited diffraction patterns assigned to the stereocomplex crystallites. In addition, for the first time it was shown that the replacement of one of the PLA partners with high molecular weight PLLA or PDLA did not hamper the stereocomplex formation. The presence of PDMAEMA blocks proved to impart hydrophilicity of the synthesized copolymers and related stereocomplexes, as determined by static water contact angle measurements.

MALDI-ToF analysis of polythiophene: use of trans-2-[3-(4-t-butyl-phenyl)-2-methyl- 2-propenylidene]malononitrile-DCTB-as matrix.

Nowadays, numerous experimental and theoretical studies are devoted to the research field of polythiophenes and other electroconjugated polymers due to the huge potentialities of those conducting polymers. Synthetic procedures are now developed to reach the highest control over both polymerization and analytical methodologies allowing an in-depth and straightforward characterization of the polymer samples without any required doubt. Mass spectrometry methodologies and in particular MALDI-ToF measurements are definitively suitable to meet the characterization requirements. In the present study, trans-2-[3-(4-t-butyl-phenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) was shown to afford better results than the reported terthiophene and dithranol matrices as far as sensitivity and signal-to-noise ratio are concerned. We tentatively proposed that the ionization of the P3HT molecules is performed by charge exchange in the condensed phase (clusters) with matrix molecule radical cations and subsequent neutral matrix molecule evaporation from the clusters. The putative key parameters to account for the really high efficiency of DCTB for the MALDI analysis of P3HT are (1) the highest ionization energy of DCTB amongst the three matrices, (2) the really high absorptivity of the matrix molecule at the laser wavelength and (3) the presence of the tertiobutyl group on the matrix molecule. The presence of this substituent is likely to decrease the intermolecular interactions in the condensed phase rendering the evaporation of the neutral matrix molecules less energy demanding. We also demonstrated for polymer samples presenting an average number molecular weight (M(n) ) below 10 000 g mol(-1) that the systematic overestimation of the low mass oligomers upon MALDI measurements ends up with wrong M(n) and polydispersity index (PDI) values. A systematic Soxhlet extraction against heptane was shown to allow the recording of absolute M(n) and PDI.

Organocatalysis Paradigm Revisited: Are Metal-Free Catalysts Really Harmless?

Catalysts are commonly used in polymer synthesis. Traditionally, catalysts used to be metallic compounds but some studies have pointed out their toxicity for human health and environment, and the removal of metal impurities from synthetic polymer is quite expensive. Organocatalysts have been intensively synthesized and are now widely used in ring-opening polymerization (ROP) reactions to address these issues. However, for most of them, there is not any evidence of their safety. The present study attempts to assess whether well-established organo-based ROP catalysts used for the preparation of FDA-approved polyesters may present a certain level of cytotoxicity. In vitro toxicity is evaluated using a methyl-thiazol-tetrazolium cytotoxicity assay on two cell models (FHs74Int and HepaRG). Among the investigated organocatalysts, only functionalized thiourea shows an important cytotoxicity on both cell models. 4-Dimethylaminopyridine (DMAP), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), and meta-(trimethylammonio)phenolate betaine (m-BE) show cytotoxicity against HepaRG cell line only at a high concentration.

Controlled room temperature ROP of L-lactide by ICl3: a simple halogen-bonding catalyst

Halogen-bonding ROP activation of L-lactide monomer by ICl3 at room temperature leads to well-controlled poly(L-lactide)s of predictable molecular weights and narrow molecular weight distributions.

Synthesis and Characterization of Nanocomposites Based on Functional Regioregular Poly(3-hexylthiophene) and Multiwall Carbon Nanotubes.

New functionalized poly(3-hexylthiophene)s (P3HT) have been designed and synthesized with the aim of increasing the dispersion of carbon nanotubes (CNT) in solutions and in thin films of semiconducting polymers. Dispersion in solution has been assessed by sedimentation tests while the thin film morphology has been analyzed by TEM and AFM. Both the physisorption of P3HT chains (via pyrene end-groups) or their chemical grafting (onto amine functions generated on the CNT surface) lead to a much better dispersion in solution and in the solid. In thin films, P3HT fibrils are observed to arrange perpendicular to the CNT surface, which can be understood on the basis of molecular modeling simulations. Finally, the effect of dispersing those P3HT/CNT nanocomposites in bulk-heterojunction P3HT-based photovoltaic devices has been evaluated.

Synthesis of poly(L-lactide) and gradient copolymers from a L-lactide/trimethylene carbonate eutectic melt

A 50 : 50 wt% mixture of L-lactide and trimethylene carbonate yields a eutectic at 21.3 °C. This mixture was exploited to prepare poly(L-lactide) homopolymers at r.t. without addition of extra solvent. The intrinsic kinetic behavior of the DBU organocatalyst also allowed for the sequential polymerization of both comonomers, leading to well defined gradient copolymers.