A new family of Type I photoinitiators based on N-heterocyclic carbene borane is introduced. The compounds are synthesized using a previously unknown homolytic B-N cleavage reaction. Three original NHC-amino borane compounds were designed and synthesized, and their UV absorption properties were assessed. All exhibit high molar extinction coefficients and frontier orbitals on the N-atom-bearing group. Their photolysis is rapid. ESR experiments clearly support the B-N homolytic bond cleavage to both NHC-BH(2)(center dot )and a delocalized radical centered mostly on sulfur. Outstanding polymerization profiles of a benchmark trifunctional acrylate monomer are noted in laminate, where the final acrylate conversions reached 70% with filtered light (lambda>300 nm).

Synthetic polymers prepared by solid-phase processes are often released from the solid support by hydrolysis, leading to an acidic alpha chain-end which can usefully be employed to perform mass spectrometry experiments in the negative ion mode. This is the case for sequence-defined polyurethanes, which exhibit very simple MS/MS pattern as deprotonated species in great contrast to data obtained in the positive ion mode. Indeed, after deprotonation of their acidic end-group, collision induced dissociation (CID) of these polymers proceeds via competitive cleavages of all carbamate bonds. This leads to a unique series of anionic fragments spaced by the mass of one of the other coding co-monomer, enabling their sequence to be readily deciphered. However, as their size increases, polyurethanes are best ionized in the positive mode but their dissociation pattern is far more complicated, with four to five fragmentation routes depending on the adducted cation. This spectral complexity could however be highly reduced when selecting precursor ions that have experienced H/Na (or any other alkali) exchange in their acidic alpha end-group: in these conditions, only one reaction is observed and yields pairs of complementary products. Mechanisms could be proposed to explain how, although part of an end-group, the acidic proton had a key role in the dissociation processes of polyurethane chains. Exchange of this proton was then further optimized by proper selection of the X- anion in the NaX salt supplemented to the electrosprayed solution. By allowing simplification of MS/MS data while avoiding signal dilution over multiple ion series, CID of these [M - H + zNa]((z-1)+) permitted to envisage reliable decoding of sequence-defined polyurethanes storing large amount of information. (C) 2019 Elsevier B.V. All rights reserved.

The synthesis and reactivity of mono- and bis-S-xanthyl NHC-boranes is reported. The new NHC-boranes are prepared through nucleophilic exchange at boron from either mono- or bis-triflyl NHC-boranes, themselves obtained by protolysis of the NHC-BH3 starting compounds. The B-H bond of the S-xanthyl NHC-boranes can be cleaved both homolytically and heterolytically, albeit the latter is more synthetically useful. The S-xanthyl NHC-boranes can reduce both aldehydes and imines. The B-S bond can also be cleaved homolytically. Under UV irradiation, the S-xanthyl NHC-boranes generate NHC-boryl radicals that can initiate radical polymerizations of acrylates.

MS/MS sequencing is an unrivaled technique to decipher binary information chemically encoded in the backbone of sequence-controlled synthetic polymers constructed with two co-monomers of different mass, arbitrarily designated as the 0- and 1-bit of the ASCII alphabet. Efficiency of this "reading" step relies however on the simplicity of MS/MS patterns, which depends on both polymer chemistry and chain length. In this context, polyurethanes (PUs) were very promising candidates as dissociation of small deprotonated oligomers (n < 8) yielded a single fragment series. The carbamate bond cleavage reaction was hence studied in details to tentatively anticipate the CID behavior of longer chains prior to optimizing their synthesis. In spite of the simplicity of MS/MS spectra, three different mechanisms were evidenced; however, they were not expected to induce MS/MS complexity when activating longer chains, as verified for sequence-controlled PUs containing up to two bytes of information (i.e., 16 co-monomers). In contrast, the ionization step appeared to be an issue: deprotonation yield of the end-group in negative ion mode electrospray was observed to strongly decrease as PU chain length increases. This sensitivity issue was addressed by introducing a second acidic end-group to allow doubly deprotonated oligomers with no impact on their CID behavior. (C) 2017 Elsevier B.V. All rights reserved.

A photoregulated phosphoramidite iterative process is studied for the synthesis of non-natural, digitally encoded oligo(phosphodiester)s. The oligomers are prepared using two reactive phosphoramidite monomers containing a 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) protected OH group. The stepwise synthesis is performed on an OH-functional soluble polystyrene support, which allows recycling by precipitation in a nonsolvent. Repeating cycles involving phosphoramidite coupling, oxidation of phosphite to phosphate, and NPPOC deprotection by light irradiation at λ = 365 nm are performed in order to prepare oligomers with different lengths and sequences. Synthesis is conducted on a micromolar scale and good recycling yields are obtained in all cases. The use of a soluble polymer support allows an in-depth characterization of the NPPOC photo-deprotection step by 1 H NMR, UV spectroscopy, and size exclusion chromatography, and thus identification of optimal synthesis conditions. After cleavage from the support, the oligo(phosphodiester)s are characterized by tandem mass spectrometry, which confirms preparation of uniform sequence-coded oligomers.

Sequence-defined oligourethanes were transformed into ATRP initiators and used for the synthesis of precision macromolecular architectures.

An innovative model-based design strategy to synthesize well-defined sequence-controlled polymers is presented, enabling selection of both the most appropriate mediating agent and reaction conditions. In combination with experimental analysis, advanced kinetic Monte Carlo simulations are conducted, allowing a visualization of the connectivity of all monomer units of ca. 10(5) individual copolymer chains. The product quality can therefore be uniquely and unambiguously predicted for the first time at the molecular level, explicitly accounting for chain-to-chain deviations. The strategy is illustrated for BlocBuilder MA-initiated nitroxide-mediated polymerization, with styrene and N-benzylmaleimide as comomomers, and is generally applicable for all reversible deactivation radical polymerization (RDRP) techniques. Further design of the nitroxide-mediating capabilities and the reaction conditions allows the realization of a targeted (multi)functionalization pattern, including an increase of the contribution of trifunctionalized chains above 75%. The reported results are interpreted in terms of the individual activation-growth-deactivation cycles and provide an unprecedented mechanistic understanding of RDRP in general.

The photoredox catalysis applied to the field of polymers and more particularly to the design of photoinitiating systems is briefly reviewed. Two novel phenylisoquinoline-based iridium complexes with fluorine substituents (bis[5-fluoro-2-(1-isoquinolinyl-κN)phenyl-κC](2,2,6,6-tetramethyl-3,5-heptanedionato-κO3,κO5)-iridium (III) (Ir_b) and bis[3,5-difluoro-2-(1-isoquinolinyl-κN)phenyl-κC](2,2,6,6-tetramethyl-3,5-heptanedionato-κO3,κO5)-iridium (III) (Ir_c) are proposed as photoredox catalysts (also called photoinitiator catalysts) and incorporated into suitable photoinitiating systems for cationic and radical polymerization. (3,4-Epoxycyclohexane)methyl-3,4-epoxycyclohexylcarboxylate (EPOX) and trimethylolpropane triacrylate (TMPTA) were used as benchmark monomers for cationic and radical photopolymerization. These new catalysts are compared to our very recently proposed unsubstituted catalyst compound: bis[2-(1-isoquinolinyl-κN)phenyl-κC](2,2,6,6-tetramethyl-3,5-heptanedionato-κO3,κO5)-iridium (III) (Ir_a). Remarkably, these catalysts exhibit improved light absorption properties and are characterized by a panchromatic behavior which ensures the photosensitivity of the polymerizable films to blue, green and red lights. The photochemical properties as well as the chemical mechanisms associated with these catalysts are investigated by ESR spin-trapping, laser flash photolysis, steady state photolysis, cyclic voltammetry and luminescence experiments. The structure/reactivity relationships as well as the substitution effect (by the fluorine) are discussed.

A small library of triazolylidene-boranes that differ only in the nature of the aryl group on the external nitrogen atom was prepared. Their reactivity as hydrogen-atom donors, as well as that of the corresponding N-heterocyclic carbene (NHC)-boryl radicals toward methyl acrylate and oxygen, was investigated by laser flash photolysis, molecular orbital calculations, and ESR spin-trapping experiments, and benchmarked relative to the already known dimethyltriazolylidene-borane. The new NHC-boranes were also used as co-initiators for the Type I photopolymerization of acrylates. This allowed a structure-reactivity relationship with regard to the substitution pattern of the NHC to be established and the role of electronic effects in the reactivity of NHC-boryl radicals to be probed. Although their rate of addition to methyl acrylate depends on their electronegativity, the radicals are all nucleophilic and good initiators for photopolymerization reactions.

We report on the use of an alkoxyamine (AA) for fabrication of functional micropatterns with complex structures by UV mask lithography. The living character of the polymer surface and the vertical spatial control of the repolymerization reaction from few tens of nanometers to few micrometers were demonstrated. The impact of the main parameters governing the controlled polymerization and the reinitiation process activated by light or heat was investigated. Micropatterning is shown to be a powerful method to investigate the physicochemical molecular phenomena. It is possible to control the polymer microstructure thickness from few tens of nanometers to few micrometers. In the last section, some applications are provided showing the potential of the AA for generating covalently bonded hydrophilic/hydrophobic micropatterns or luminescent surfaces. This demonstrates the high versatility and interest of this route.

ABSTRACT This article reports on the presumably first use of iron complexes (FeC) as potential photocatalysts for controlled radical photopolymerization reactions (CRP2). Three compounds were designed and investigated. Good linear evolutions of the molecular weight (Mn) with the conversion were observed. A comparison was provided with a reference iridium (III) complex [Ir(ppy)3 where ppy stands for 2‐phenylpyridine]. The on/off photopolymerization experiments highlight the presence of dormant species and a re‐initiation on demand upon irradiation. This unique re‐initiation property was used for the modification of surfaces (hydrophilic/hydrophobic properties) and surface patterning as well as the synthesis of a block co‐polymer (PMMA‐b‐PBA). A comparative analysis of the behavior of these iron complexes in thermally and photochemically activated polymerization was provided. The chemical mechanisms were studied by steady state photolysis, laser flash photolysis, cyclic voltammetry, luminescence quenching, and electron spin resonance experiments. A catalytic cycle was proposed with two steps: (i) the oxidation of the FeC excited state by an alkyl halide and (ii) the reduction by the oxidized form (FeC°+) by an amine or the macroradicals leading to the regeneration of the catalyst. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54 , 702–713

The highly active photocatalyst [Au2(dppm)2]Cl2 is able to efficiently promote controlled/living photoATRP of acrylates and methacrylates.

1,3-Bis(dicyanomethylidene) indane is presented as a new initiator for ring opening polymerization of epoxides at RT. This compound behaves as a strong acid (AH) with an associated basic form (A(-)) that does not inhibit the propagation of the cationic polymerization. Remarkably, A(-) is characterized by a strong visible light absorption and can also photosensitize iodonium salt decomposition. A new iodonium salt based on A(-)as a counter-anion is proposed. This latter compound exhibits unusual properties: (i) excellent absorption in the 300-700 nm wavelength range and (ii) a free radical initiating ability for lambda > 300 nm. The chemical mechanisms are investigated by ESR, fluorescence and steady state photolysis experiments.

A new iridium complex (nIr) was designed and investigated as a photoinitiator catalyst for radical and cationic polymerizations upon very soft irradiation.

In the present paper, the photoredox catalysis is presented as a unique approach in the field of photoinitiators of polymerization. The principal photocatalysts already reported as well as the typical oxidation and reduction agents used in both reductive or oxidative cycles are gathered. The chemical mechanisms associated with various systems are also given. As compared to classical iridium-based photocatalysts which are mainly active upon blue light irradiation, a new photocatalyst Ir(piq) 2 (tmd) (also known as bis(1-phenylisoquinolinato- N , C 2’ )iridium(2,2,6,6-tetramethyl-3,5-heptanedionate) is also proposed as an example of green light photocatalyst (toward the long wavelength irradiation). The chemical mechanisms associated with Ir(piq) 2 (tmd) are investigated by ESR spin-trapping, laser flash photolysis, steady state photolysis, cyclic voltammetry and luminescence experiments.

New thiophene derivatives (THs) are prepared and proposed here as new photoinitiators in combination with an iodonium salt for the cationic polymerization of vinylethers. They contain electron donor and electron acceptor (D–A) moieties and exhibit red‐shifted absorption spectra. They allow the use of a long‐wavelength excitation at 532 nm using a laser diode. Irradiation from a green light‐emitting diode (LED) at 514 nm can also be used. The high reactivity upon irradiation from the low‐intensity green LED highlights the high reactivity of the proposed structures. Interesting polymerization profiles (with conversions up to 70%) are obtained. The initiation step mechanisms are analyzed by electron spin resonance (ESR), fluorescence measurements, steady‐state photolysis, and laser flash photolysis experiments. image

A new photosensitive alkoxyamine is synthetized and introduced to induce living radical polymerization mediated by UV irradiation (nitroxide-mediated photo­polymerization). This system can be used to produce functional micro- and nanopatterns with complex structures by lithography, including laser direct writing. This is a unique feature in photo-controlled micropatterning with versatile topography and chemistry. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

The combination of thermally-and photochemically-induced polymerization using light sensitive alkoxy-amines 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.

The B-S bond in N-heterocyclic carbene (NHC)-boryl sulfides can be cleaved homolytically to NHC-boryl or NHC-thioboryl and thiyl radicals using light, either directly around 300 nm or with a sensitizer at a longer wavelength (>340 nm). In contrast, the electrochemical reductive cleavage of the B-S bond is difficult. This easy photolytic cleavage makes the NHC-boryl sulfides good type I photopolymerization initiators for the polymerization of acrylates under air.