A pH‐Triggered Polymer Degradation or Drug Delivery System by Light‐Mediated Cis / Trans Isomerization of o ‐Hydroxy Cinnamates

A new methodology for the pH-triggered degradation of polymers or for the release of drugs under visible light irradiation based on the cyclization of ortho-hydroxy-cinnamates (oHC) to coumarins is described. The key oHC structural motif can be readily incorporated into the rational design of novel photocleavable polymers via click chemistry. This main-chain moiety undergoes a fast photocleavage when irradiated with 455 nm light provided that a suitable base is added. A series of polyethylene glycol-alt-ortho-hydroxy cinnamate (polyethylene glycol (PEG)n-alt-oHC)-based polymers are synthesized and the time-dependent visible-light initiated cleavage of the photoactive monomer and polymer is investigated in solution by a variety of spectroscopic and chromatographic techniques. The photo-degradation behavior of the water-soluble poly(PEG2000-alt-oHC) is investigated within a broad pH range (pH = 2.1–11.8), demonstrating fast degradation at pH 11.8, while the stability of the polymer is greatly enhanced at pH 2.1. Moreover, the neat polymer shows long-term stability under daylight conditions, thus allowing its storage without special precautions. In addition, two water-soluble PEG-based drug-carrier molecules (mPEG2000-oHC-benzhydrol/phenol) are synthesized and used for drug delivery studies, monitoring the process by UV–vis spectroscopy in an ON/OFF intermittent manner

Development of photocleavable block copolymers as precursors for functional nanomaterials

Block copolymers have become nowadays powerful tools for the preparation of nanostructured materials. They are indeed able to self-assemble at the nanoscale into well-ordered structures that can be used, for example, for the preparation of nanoporous materials by selectively removing the minor phase. These materials exhibit the pore topology and the pore size of their parent structures and can be further used as separation membranes or templates for other nanomaterials. Most methods reported up to now for the creation of nanopores rely on the degradation of the minor block and offer thus a rather poor control over the functionality of the pore walls. In this thesis, a new approach towards nanoporous materials displaying chemical functionalities has been investigated. The first step of the project was the synthesis of block copolymers containing one or several o-nitrobenzyl photocleavable moieties. After their synthesis, their behavior upon UV irradiation has been studied in solution in order to determine the optimal conditions for their photocleavage. Then, the different synthesized photocleavable block copolymers have been self-assembled in thin films presenting a cylindrical morphology and the conditions of annealing leading to the desired perpendicular orientation of the cylinders have been optimized. Finally the creation of porosity after irradiation and removal of the minor phase has been studied and demonstrated.(CHIM 3) -- UCL, 201

A versatile strategy for the synthesis of block copolymers bearing a photocleavable junction

Various block copolymers in which the blocks are held together by a photocleavable junction have been synthesized via a one-pot simultaneous ATRP-CuAAC "click" reaction process, and their easy photocleavage has been demonstrated

Highly beta-(E)-selective hydrosilylation of terminal and internal alkynes catalyzed by a (IPr)Pt(diene) complex.

The regioselective hydrosilylation of terminal and internal alkynes catalyzed by the novel (IPr)Pt(AE) ( 7) (IPr = bis(2,6-diisopropylphenyl)imidazo-2-ylidene, AE = allyl ether) complex is presented. The (IPr)Pt(AE) catalyst displays enhanced activity and regioselectivity for the hydrosilylation of terminal and internal alkynes with low catalyst loading (0.1 to 0.05 mol %) when compared to the parent (IPr)Pt(DVDS) complex ( 6) (DVDS = divinyltetramethyldisiloxane). The reaction leads to exquisite regioselectivity in favor of the cis-addition product on the less hindered terminus of terminal and internal alkynes. The solvent effects were examined for the difficult hydrosilylation of benzylpropargyl ether. In light of the observed product distribution and kinetic data, a mechanistic scheme is proposed involving two competing catalytic cycles. One cycle leads to high regioselectivities while the other, having lost the stereodirecting IPr carbene ligand, displays low regiocontrol and activities. The importance of this secondary catalytic cycle is either caused by the strong coordinating ability of the alkyne or by the low reactivity of the silane or both

Synthesis and self-assembly of diblock copolymers bearing 2-nitrobenzyl photocleavable side groups

The light-responsive behavior in solution and in thin films of block copolymers bearing 2-nitrobenzyl photocleavable esters as side groups is discussed in this article. The polymers were synthesized by grafting 2-nitrobenzyl moieties onto poly(acrylic acid)-block-polystyrene (PAA-b-PS) precursor polymers, leading to poly(2-nitrobenzyl acrylate-random-acrylic acid)-block-polystyrene (P(NBA-r-AA)-b-PS) block copolymers. The UV irradiation of the block copolymers in a selective solvent for PS led to the formation of micelles that were used to trap hydrophilic molecules inside their core (light-induced encapsulation). In addition, thin films consisting of light-responsive P(NBA-r-AA) cylinders surrounded by a PS matrix were achieved by the self-assembly of P(NBA-r-AA)-b-PS copolymers onto silicon substrates. Exposing these films to UV irradiation generates nanostructured materials containing carboxylic acids inside the cylindrical nanodomains. The availability of these chemical functions was demonstrated by reacting them with a functional fluorescent dye. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 Light-responsive poly(2-nitrobenzyl acrylate-random-acrylic acid)-block-polystyrene (P(NBA-r-AA)-b-PS) block copolymers (P(NBA-r-AA)-b-PS) have been synthesized and further self-assembled in solution as well as in thin films. In solution, the block copolymers were used to encapsulate hydrophilic molecules inside the core of light-induced micelles. In addition, light-responsive nanostructured thin films have been prepared onto silicon substrates. Exposing these films to UV irradiation generates chemical functionalities inside the photo-responsive nanodomains. Copyright © 2011 Wiley Periodicals, Inc