Yohann Guillaneuf

Photoredox catalysis using a new iridium complex as an efficient toolbox for radical, cationic and controlled polymerizations under soft blue to green lights

A new iridium complex (nIr) was designed and investigated as a photoinitiator catalyst for radical and cationic polymerizations upon very soft irradiations (lights ranging from 457 to 532 nm). A ring-opening polymerization (ROP) of an epoxy monomer was easily promoted through the interaction between nIr and an iodonium salt (Iod) upon light. The addition of N-vinylcarbazole (NVK) enhances the performance. In radical polymerization, nIr can be efficient in combination with phenacyl bromide (PBr) and optionally an amine: these photoinitiating systems work according to an original oxidative cycle and a regeneration of nIr is observed. A control of the methyl methacrylate polymerization (conducted under a 462 nm light) with 1.2–1.6 polydispersity indexes was displayed. Surface modifications by direct laser write was also easily carried out for the first time through surface re-initiation experiments, i.e. the dormant species being reactivated by light in the presence of nIr; the polymer surfaces were analyzed by XPS. The chemical mechanisms were examined through laser flash photolysis, NMR, ESR and size exclusion chromatography experiments.

Nitroxide-Mediated Radical Ring-Opening Copolymerization: Chain-End Investigation and Block Copolymer Synthesis

Well-defined, degradable copolymers are successfully prepared by nitroxide-mediated radical ring opening polymerization (NMrROP) of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) or methyl methacrylate (MMA), a small amount of acrylonitrile (AN) and cyclic ketene acetals (CKAs) of different structures. Phosphorous nuclear magnetic resonance allows in-depth chain-end characterization and gives crucial insights into the nature of the copoly-mer terminal sequences and the living chain fractions. By using a small library of P(OEGMA-co-AN-co-CKA) and P(MMA-co-AN-co-CKA) as macroinitiators, chain extensions with styrene are performed to furnish (amphiphilic) block copolymers comprising a degradable segment.

Heterogeneous modification of chitosan via nitroxide-mediated polymerization

Chitosan (CS) was modified by SG1-based nitroxide-mediated polymerization under heterogeneous conditions. After introduction of acrylamide and/or acrylate functions onto the CS backbone followed by intermolecular 1,2 radical addition of the BlocBuilder alkoxyamine (CS–BB), methyl methacrylate (MMA) in the presence of a small amount of acrylonitrile (AN) or sodium 4-styrenesulfonate (SS) was polymerized by nitroxide-mediated polymerization (NMP). ESR and free-solution capillary electrophoresis confirmed the synthesis of CS–BB. The successful synthesis of CS-g-P(MMA-co-AN) and CS-g-PSS grafted copolymers was proved by TGA and solid-state NMR spectroscopy with ca. 20 to 30 wt% of grafted synthetic polymer in the final product.

Structural effects on the photodissociation of alkoxyamines

The search for photosensitive alkoxyamines represents a huge challenge. The key parameters governing the cleavage process remain unknown. The dissociation process of light sensitive alkoxyamines is studied as a function of their chemical structures. The photochemical properties of 6 selected compounds are investigated by ESR and laser flash photolysis. It is found that (i) the selectivity of the cleavable N-O vs. C-O bond and (ii) the efficiency of the nitroxide formation are strongly related to the alkoxyamine structure. The distance between the chromophore and the aminoxy group is a key parameter for an efficient pathway of the radical generation as displayed by the photopolymerization ability of these alkoxyamines.

Nitroxide-Mediated Polymerization of Methacrylic Esters: Insights and Solutions to a Long-Standing Problem.

Nitroxide-mediated polymerization (NMP) is one of the most powerful reversible deactivation radical polymerization techniques and has incredibly gained in maturity and robustness over the last decades. However, control of methacrylic esters is one of the different aspects of NMP that still requires improvement. This family of monomers always represented an important challenge for NMP, despite the many different nitroxide structures that have been designed over the course of time. This Review aims to present the most successful strategies directed toward the control of the NMP technique of methacrylic esters and especially methyl methacrylate. NMP-derived materials comprising uncontrolled methacrylate segments will also be discussed.

Nitroxide mediated polymerization of methacrylates at moderate temperature

In this communication we report the first homopolymerization of a variety of methacrylates by an NMP process at moderate temperature (40–50 °C), using an easily accessible and inexpensive nitroxide precursor. The combination of a low temperature azo-initiator with a hindered nitroso-compound produces a mixture of hindered nitroxides in the polymerization medium that act as efficient polymerization control agents. Results of Electron Spin Resonance (ESR) spectroscopy experiments combined with mass spectrometric studies support the proposed in situ NMP mechanism. The hindered structure of the nitroxides formed in situ is believed to be responsible for the efficiency of the process by allowing it to proceed at low temperature, therefore limiting the side reactions generally observed in NMP of methacrylates.

Scope and limitations of the nitroxide-mediated radical ring-opening polymerization of cyclic ketene acetals

The ring-opening polymerization of cyclic ketene acetals (CKAs) by controlled radical mechanisms represents an alternative route for the synthesis of aliphatic polyesters. For the first time, 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) and 2-methylene-4-phenyl-1,3-dioxolane (MPDL) were homopolymerized by nitroxide mediated polymerization (NMP), from the commercially available SG1-based BlocBuilder MA alkoxyamine. Various experimental conditions (i.e., reaction temperature, nature of solvent, and nature of the alkyl initiating radical) were varied to determine the optimized conditions in terms of polymerization kinetics and living character of the final polymer. Chain-end extensions from either PS-SG1 or PBMDO-SG1 were also performed in order to furnish PS-b-PBMDO and PBMDO-b-PS, respectively, thus demonstrating the synthesis of block copolymers comprising a CKA block. In order to have a better insight into the polymerization mechanism, the occurrence of side reactions was analyzed by 31P NMR spectroscopy and ESI-MS. It was supposed that the ketal-based macroradical could be irreversibly trapped by nitroxide and thus the corresponding macroalkoxyamine decomposed by CO–N bond dissociation. DFT calculations as well as PREDICI modeling were also undertaken in order to support this hypothesis.

Understanding and improving direct UV detection of monosaccharides and disaccharides in free solution capillary electrophoresis

Direct UV detection of carbohydrates in free solution capillary electrophoresis at 270 nm is made possible by a photo-oxidation reaction. Glucose, rhamnose and xylose were shown to have unique UV absorption spectra hypothesizing different UV absorbing intermediates for their respective photo-oxidation. NMR spectroscopy of the photo-oxidation end products proved they consisted of carboxylates and not malondialdehyde as previously theorized and that oxygen thus plays a key role in the photo-oxidation pathway. Adding the photo-initiator Irgacure(®) 2959 in the background electrolyte increased sensitivity by 40% at an optimum concentration of 1×10(-4) mM and 1×10(-8) mM for conventional 50 μm i.d. capillaries and for the corresponding extended light path capillaries, respectively.

Novel polymer synthesis methodologies using combinations of thermally- and photochemically-induced nitroxide mediated polymerization

The combination of thermally- and photochemically-induced polymerization using light sensitive alkoxyamines was investigated. The thermally driven polymerizations were performed via the cleavage of the alkoxyamine functionality, whereas the photochemically-induced polymerizations were carried out either by nitroxide mediated photo-polymerization (NMP2) or by a classical type II mechanism, depending on the structure of the light-sensitive alkoxyamine employed. Once the potential of the various structures as initiators of thermally- and photo-induced polymerizations was established, their use in combination for block copolymer syntheses was investigated. With each alkoxyamine investigated, block copolymers were successfully obtained and the system was applied to the post-modification of polymer coatings for application in patterning and photografting.

Simulation of radical polymerization of methyl methacrylate at room temperature using a tertiary amine/BPO initiating system

The decomposition kinetics of the initiation reaction between benzoyl peroxide and a tertiary amine, either dimethyl-p-toluidine or dihydroxyethyl-p-toluidine, was studied by infrared spectroscopy and an Arrhenius plot was established. Based on these results, a model was developed for the polymerization of methyl methacrylate at room temperature. The model used both free volume and empirical models for propagation, termination and several side reactions. The model described the conversion for a very broad range of reaction conditions and the results were in good agreement with the experimental data. This study showed significant differences between dimethyl-p-toluidine and dihydroxyethyl-p-toluidine with respect to the gel time and the molar mass of poly(methyl methacrylate).