Bart Dervaux

Heterogeneous azide–alkyne click chemistry: towards metal-free end products

Heterogeneous copper catalyzed azide–alkyne click chemistry (CuAAc) has been a quickly emerging research field during the last couple of years as it shows many advantages in comparison to its homogeneous counterpart. In this Minireview, an overview of the state-of-the-art is presented for the first time. For the sake of completeness, not only successful heterogeneous supports but also systems that particularly failed will be discussed. Furthermore, the future prospects and challenges with regard to the application of heterogeneous CuAAC are highlighted.

Design and Use of Organic Nanoparticles Prepared from Star-Shaped Polymers with Reactive End Groups

Star-shaped poly(isobornyl acrylate) (PiBA) was prepared by atom transfer radical polymerization (ATRP) using multifunctional initiators. The optimal ATRP conditions were determined to minimize star-star coupling and to preserve high end group functionality (>90%). Star-shaped PiBA with a narrow polydispersity index was synthesized with 4, 6, and 12 arms and of varying molecular weight (10,000 to 100,000 g x mol(-1)) using 4 equiv of a Cu(I)Br/PMDETA catalyst system in acetone. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis, NMR spectroscopy, and size exclusion chromatography (SEC) confirmed their controlled synthesis. The bromine end group of each arm was then transformed to a reactive end group by a nucleophilic substitution with methacrylic acid or cinnamic acid (conversion >90%). These reactive star polymers were used to prepare PiBA nanoparticles by intramolecular polymerization of the end groups. The successful preparation of this new type of organic nanoparticles on a multigram scale was proven by NMR spectroscopy and SEC. Subsequently, they have been used as additives for linear, rubbery poly(n-butyl acrylate). Rheology measurements indicated that the viscoelastic properties of the resulting materials can be fine-tuned by changing the amount of incorporated nanoparticles (1-20 wt %), as a result of the entanglements between the nanoparticles and the linear polymers.

Morphological transition during the thermal deprotection of poly(isobornyl acrylate)-b-poly(1-ethoxyethyl acrylate)

A set of poly(isobornyl acrylate)--poly(1-ethoxyethyl acrylate) polymers has been prepared by atom transfer radical polymerization. The 1-ethoxyethyl protecting group can be removed by a mild thermal treatment yielding the poly(acrylic acid) segment. The thin film morphological behavior of selected block copolymers was studied for as well as deprotected block copolymers using atomic force microscopy (AFM). Low-temperature thermal treatment yielded strongly phase-separated cylindrical features whereas treatment at temperatures above the glass transition temperature of the individual polymer blocks resulted in the initial generation of a similar phase contrast followed by a decrease in phase contrast caused by selective surface enrichment of the more hydrophobic poly(isobornyl acrylate) segment.

From one-pot stabilisation to in situ functionalisation in nitroxide mediated polymerisation: an efficient extension towards atom transfer radical polymerisation

A one-pot controlled method for the nitroxide end-group removal from synthetic polymers prepared by nitroxide mediated polymerisation (NMP) is reported. The strategy relies on the controlled addition of compounds such as thiols, radical initiators and carbon tetrabromide with high chain transfer constants. From a practical point of view, when the desired molar mass and conversion are reached, 1 to 10 equivalents of the transfer agent compared to the nitroxide are added and a few minutes later, after transformation of all chain-ends, the reaction is quenched. The versatility of the procedure was successfully tested with a wide range of monomers (styrene (S), isobornyl acrylate (iBA) or methyl methacrylate (MMA)) and nitroxides (2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide (SG1)). The removal of the nitroxide end-group proceeds with high fidelity for all the transfer agents studied, while at the same time the thermal stability of the resulting polymer chains increases when thiols are employed. Furthermore, a functional group that allows for chain extension by atom transfer radical polymerisation (ATRP) has been introduced through the direct synthesis of bromine terminated macroinitiators via a chain transfer reaction with carbon tetrabromide.

From Novel Block-Like Copolymers to Reactive Nanoparticles: ATRP and “Click” Chemistry as Synthetic Tools

In this chapter, we report on the synthesis and characterization of well-defined amphiphilic block copolymers, ‘block-like’ copolymers and star copolymers composed of poly(isobornyl acrylate) (PiBA) and poly(acrylic acid) (PAA) by ATRP. As PiBA polymers exhibit interesting physical characteristics, we report first a detailed study of the homopolymerization of iBA. The precursor monomers 1-ethoxyethyl acrylate as well as tert-butyl acrylate have been used to synthesize the precursor polymers for the PiBA-co-PAA block copolymers. Furthermore, a combination of ATRP and ‘click’ chemistry was used to prepare block and graft copolymers using a modular approach. The PiBA-PAA block and ‘block-like’ copolymers were investigated as pigment stabilizers for aqueous pigment dispersions. In the second part of the research, well-defined PiBA star copolymers were prepared, and reactive nanoparticles were obtained by end group modification of the PiBA star polymers with reactive moieties. Finally, the control of the visco-elastic properties by the incorporation of these nanoparticles in an acrylate polymer matrix was investigated.

ROP of cyclic amines and sulfides

Cyclic amines and cyclic sulfides represent two large families of monomers. The variety of structures, and hence variety of physical properties of the corresponding polymers, stems from the variation of ring size and from the possibility of placing substituents on the heterocycle. In this chapter, the mechanism of polymerization of different monomer types is described, with emphasis on control of the polymer structures formed. This control applies to molecular weight and molecular weight distribution (MWD), the stereochemistry of the polymerization, the architecture of the polymers, and the nature of the polymer chain end groups. A short paragraph on the ring-opening polymerization (ROP) of cyclic disulfides is included.