Organocatalyzed Phospha-Michael Addition: A Highly Efficient Synthesis of Customized Bis(acyl)phosphane Oxide Photoinitiators.

Addition of the P-H bond in bis(mesitoyl)phosphine, HP(COMes)2 (BAPH), to a wide variety of activated carbon-carbon double bonds as acceptors was investigated. While this phospha-Michael addition does not proceed in the absence of an additive or catalyst, excellent results were obtained with stoichiometric basic potassium or caesium salts. Simple amine bases can be employed in catalytic amounts, and tetramethylguanidine (TMG) in particular is an outstanding catalyst that allows the preparation of bis(acyl)phosphines, R-P(COMes)2 , under very mild conditions in excellent yields after only a short time. All phosphines RP(COMes)2 can subsequently be oxidized to the corresponding bis(acyl)phosphane oxides, RPO(COMes)2 , a substance class belonging to the most potent photoinitiators for radical polymerizations known to date. Thus, a simple and highly atom economic method has been found that allows the preparation of a broad range of photoinitiators adapted to their specific field of application even on a large scale.

Bismesitoylphosphinic Acid (BAPO-OH): A Ligand for Copper Complexes and Four-Electron Photoreductant for the Preparation of Copper Nanomaterials.

Bismesitoylphosphinic acid, (HO)PO(COMes)2 (BAPO-OH), is an efficient photoinitiator for free-radical polymerizations of olefins in aqueous phase. Described here are the structures of various copper(II) and copper(I) complexes with BAPO-OH as the ligand. The complex CuII (BAPO-O)2 (H2 O)2 is photoactive, and under irradiation with UV light in aqueous phase, it serves as a source of metallic copper in high purity and yield (>80 %). Simultaneously, the radical polymerization of acrylates can be initiated and allows the preparation of nanoparticle/polymer nanocomposites in which the metallic Cu nanoparticles are protected against oxidation. The determination of the stoichiometry of the photoreductions suggests an almost quantitative conversion from CuII into Cu0 with half an equivalent of BAPO-OH, which serves as a four-electron photoreductant.

Star-shaped Polymers through Simple Wavelength-Selective Free-Radical Photopolymerization.

Star-shaped polymers represent highly desired materials in nanotechnology and life sciences, including biomedical applications (e.g., diagnostic imaging, tissue engineering, and targeted drug delivery). Herein, we report a straightforward synthesis of wavelength-selective multifunctional photoinitiators (PIs) that contain a bisacylphosphane oxide (BAPO) group and an α-hydroxy ketone moiety within one molecule. By using three different wavelengths, these photoactive groups can be selectively addressed and activated, thereby allowing the synthesis of ABC-type miktoarm star polymers through a simple, highly selective, and robust free-radical polymerization method. The photochemistry of these new initiators and the feasibility of this concept were investigated in unprecedented detail by using various spectroscopic techniques.

Synthesis of new bis(acyl)phosphane oxide photoinitiators for the surface functionalization of cellulose nanocrystals.

A new synthesis of bis(acyl)phosphane oxide (BAPO) photoinitiators was developed which can be used to functionalize cellulose nanocrystal surfaces for polymer grafting. Hybrid materials with excellent graft yields can be rapidly obtained under mild and acid-free conditions.

Simple one-pot syntheses of water-soluble bis(acyl)phosphane oxide photoinitiators and their application in surfactant-free emulsion polymerization.

The sodium salt of the new bis(mesitoyl)phosphinic acid (BAPO-OH) can be prepared in a very efficient one-pot synthesis. It is well soluble in water and hydrolytically stable for at least several weeks. Remarkably, it acts as an initiating agent for the surfactant-free emulsion polymerization (SFEP) of styrene to yield monodisperse, spherical nanoparticles. Time-resolved electron paramagnetic resonance (TR-EPR) and chemically induced electron polarisation (CIDEP) indicate preliminary mechanistic insights.