Photocleavable Block Copolymers Research Articles

Naked micelles: well-defined polymer nanoparticles from photo-cleavable block copolymer micelles

We report that photo-cleaving the corona of block copolymer micelles provides well-defined nanoparticles with surface charges accessible for electrostatic modification.

Synthesis of Photocleavable Block Copolymers for UV Induced Foaming

Synthesis of Photocleavable Block Copolymers for UV Induced Foaming

Synthesis and Self-Aggregation of Poly(2-ethyl-2-oxazoline)-Based Photocleavable Block Copolymer: Micelle, Compound Micelle, Reverse Micelle, and Dye Encapsulation/Release

We report on the synthesis of photocleavable poly(2-ethyl-2-oxazoline)-block-poly(2-nitrobenzyl acrylate) (PEtOx-b-PNBA) block copolymers (BCPs) with varying compositions via combination of microwave-assisted cationic ring-opening polymerization (CROP) and atom transfer radical polymerization (ATRP) using α-bromoisobutyryl bromide as an orthogonal initiator. The amphiphilic nature of this BCP causes them to self-assemble into primary micelles in THF/H2O, which further undergo secondary aggregation into nanostructured compound micelles as established through DLS, FESEM, and TEM. Upon UV irradiation (λ = 350 nm), the photocleavage of the PNBA block of the PEtOx-b-PNBA BCP takes place, and that leads to the formation of the doubly hydrophilic poly(2-ethyl-2-oxazoline)-b-poly(acrylic acid) (PEtOx-b-PAA) BCP causing the rupture of compound micelles as confirmed by spectroscopic and microscopic techniques. Encapsulation of a model hydrophobic guest molecule, nile red (NR), into the photocleavable BCP micellar core in aqueous solution and its UV-induced release is also investigated by fluorescence emission measurements. PEtOx-b-PNBA BCP amphiphiles are also shown to self-assemble into spherical nanostructures (∼90 nm) in dichloromethane as established by DLS and TEM analysis. These are referred to as reverse micelles and are able to encapsulate anionic hydrophilic dye, Eosin B, and facilitate its solubilization in organic media.

Distortion of Ultrathin Photocleavable Block Copolymer Films during Photocleavage and Nanopore Formation.

Highly ordered block copolymer thin films have been studied extensively during the last years because they afford versatile self-assembled morphologies via a bottom-up approach. They promise to be used in applications such as polymeric membranes or templates for nanostructured materials. Among the block copolymer structures, perpendicular cylinders have received strong attention due to their ability to fabricate highly ordered nanopores and nanowires. Nanopores can be created from a thin block copolymer film upon the removal of one block by selective etching or by dissolution of one polymer block. Here we demonstrate the utilization of polystyrene-block-poly(ethylene oxide) diblock copolymer (PS-hν-PEO) with an ortho-nitrobenzyl ester (ONB) as the photocleavable block-linker to create highly ordered thin films. Removal of the PEO block by choosing an appropriate solvent upon photocleavage is expected to yield arrays of nanopores decorated with functional groups, thus lending itself to adsorption or filtration uses. While the feasibility of this approach has been demonstrated, it is crucial to understand the influence of removal conditions (i.e., efficiency of photocleavage as well as best washing solvent) and to evaluate changes in the surface topology and inner structure upon photocleavage. To this end, the time dependence evolution of the surface morphology of block copolymer thin films was studied using grazing-incidence small-angle X-ray scattering (GISAXS) technique in combination with scanning probe microscopy.

Bio-recognizable and photo-cleavable block copolymers based on sugar and poly(4-substituted-ε-caprolactone) bearing a photo-cleavable junction

In this study, we synthesized bio-recognizable and photo-cleavable amphiphilic block copolymers containing photodegradable linkers, 5-hydroxy-2-nitrobenzyl alcohol, as junction points between bio-recognizable hydrophilic glucose (or maltose) and hydrophobic poly(4-substituted-e-caprolactone) chains, by using a combination of ring-opening polymerization and nucleophilic substitution reactions. When the polymer solutions were exposed to ultraviolet (UV) irradiation, substantial structural and morphological changes were observed in the particles. The copolymers were biodegradable and biocompatible, and they could self-assemble into spherical photo-responsive micelles. Fluorescence emission measurements indicated the release of Nile red, a hydrophobic dye, encapsulated by the Glyco-ONB-PXCL micelles, in response to irradiation caused by the disruption of the micelles. Selective lectin binding experiments confirmed that the glycosylated Glyco-ONB-PXCL could be used to bio-recognition applications. The nanoparticles were associated with negligible levels of toxicity at concentrations of less than 30 μg mL−1. The confocal microscopy and flow cytometry results showed that the uptake of doxorubicin (DOX)-loaded micelles by HeLa cells was faster than that of free DOX.

Synthesis and characterization of thermo-responsive and photo-cleavable block copolymers as nanocarriers

In this study, we synthesized thermo-responsive and photo-cleavable amphiphilic block copolymers containing photodegradable linkers as junction points between hydrophilic and hydrophobic chains.

Functionalized Stimuli-Responsive Nanocages from Photocleavable Block Copolymers

The light-induced formation of pH and temperature-responsive poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) nanocages is demonstrated here. The strategy is based on the self-assembly in aqueous solutions of a photocleavable poly(tert-butyl acrylate)-hv-poly[2-(dimethylamino)ethyl methacrylate] block copolymer (PtBA-hv-PDMAEMA, where -hv- is the photocleavable junction) into spherical micelles, followed by first PDMAEMA cross-linking by a bis-iodo compound and then by UV light irradiation. The exposure to light induces the cleavage of the junction between the PtBA core and the cross-linked PDMAEMA shell of the micelles. The PtBA block is then extracted to obtain the desired nanocages. The size change of the nanocages in response to pH and temperature is investigated by dynamic light scattering. Finally, the ability to functionalize the internal cavity of the nanocages is demonstrated.

Line Patterns from Cylinder‐Forming Photocleavable Block Copolymers

A robust route for the preparation of nanoscopic line patterns from polystyrene-block-poly(ethylene oxide) featuring a photocleavable o-nitrobenzyl ester junction is demonstrated. After mild UV (λ = 365 nm) exposure and selective removal of the PEO microdomains, the polymer trench patterns are used as scaffold to fabricate highly ordered arrays of silica or Au line patterns.

Synthesis of photocleavable poly(methyl methacrylate-block-d -lactide) via atom-transfer radical polymerization and ring-opening polymerization

The synthesis and characterization of a photocleavable block copolymer containing an ortho-nitrobenzyl (ONB) linker between poly(methyl methacrylate) and poly(d-lactide) blocks is presented here. The block copolymers were synthesized via atom transfer radical polymerization (ATRP) of MMA followed by ring-opening polymerization (ROP) of d-Lactide and ROP of d-lactide followed by ATRP of MMA from a difunctional photoresponsive ONB initiator, respectively. The challenges and limitations during synthesis of the photocleavable block copolymers using the difunctional photoresponsive ONB initiator are discussed. The photocleavage of the copolymers occurs under mild conditions by simple irradiation with 302 nm wavelength UV light (Relative intensity at 7.6 cm: 1500 μW/cm2) for several hours. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4309–4316

Functionalized Nanoporous Thin Films and Fibers from Photocleavable Block Copolymers Featuring Activated Esters

A series of poly(pentafluorophenyl (methyl)acrylates)-block-poly(ethylene oxide) with o-nitrobenzyl ester photocleavable junctions (PPFP(M)A-hv-PEO) were synthesized by RAFT polymerization. The block copolymers were used to fabricate thin films and fibers by spin-coating and electrospinning, respectively. After solvent annealing, UV exposure, and washing with methanol/water to remove the minor PEO block, nanoporous structures were obtained. Both the porous thin films and fibers remained reactive to amine substitution of the pentafluorophenyl esters under mild conditions, which was confirmed by XPS, fluorescence confocal microscopy, FT-IR, and contact angle measurements.

Amphiphilic photocleavable block copolymers based on monomethyl poly(ethylene glycol) and poly(4-substituted-ε-caprolactone): synthesis, characterization, and cellular uptake

This paper presents the synthesis of a novel amphiphilic block copolymer containing photodegradable linkers as junction points between hydrophilic and hydrophobic chains. MPEG-ONB-PXCL block copolymers were synthesized by a combination of ROP and “clicks” from a difunctional photoresponsive initiator (ONB). The copolymers are biodegradable and biocompatible, and can self-assemble into photoresponsive micelles. When polymer solutions were exposed to UV, we observed significant changes in the structure and morphology of particles. Fluorescence emission measurements showed that Nile red (NR), a hydrophobic dye, encapsulated by the MPEG-ONB-PXCL micelles, is released upon irradiation because of disruption of the micelles. Light-triggered bursts were observed for Indomethacin (IMC)-loaded MPEG-ONB-PXCL micelles upon at 30 min of light irradiation. No significant toxicity of these nanoparticles was found, at concentrations up to 1000 μg mL−1, before or after light irradiation. The doxorubicin (DOX)-loaded micelles facilitated improved uptake of DOX by HeLa cells within 60 min, and were retained primarily in the cytoplasm.

Multiresponsive Micellar Systems from Photocleavable Block Copolymers.

This contribution describes the synthesis and associating behavior in water of a multiresponsive amphiphilic diblock copolymer. This copolymer is composed of an hydrophobic photocleavable poly(para-methoxyphenacyl methacrylate) block (PMPMA) and a hydrophilic thermosensitive poly[(oligo ethylene glycol)methacrylate] block (POEGMA). The PMPMA-b-POEGMA copolymer forms micelles with a PMPMA core and a POEGMA corona in water. Light irradiation leads to the transformation of PMPMA into poly(methacrylic acid) (PMAA) and to the disruption of the initial micelles. The response of the accordingly obtained PMAA-b-POEGMA copolymer to pH, temperature, calcium (Ca2+), and phosphate (PO43-) ions is demonstrated.

O-Nitrobenzyl Alcohol Derivatives: Opportunities in Polymer and Materials Science

Polymers featuring photolabile groups are the subject of intense research because they allow the alteration of polymer properties simply by irradiation. In particular, the o-nitrobenzyl group (o-NB) is utilized frequently in polymer and materials science. This Perspective pays particular attention to the increasing utilization of this chemical group in polymer chemistry. It covers the use of (i) o-NB-based cross-linkers for photodegradable hydrogels, (ii) o-NB side chain functionalization in (block) copolymers, (iii) o-NB side chain functionalization for thin film patterning, (iv) o-NB for self-assembled monolayers, (v) photocleavable block copolymers, and (vi) photocleavable bioconjugates. We conclude with an outlook on new research directions in this rapidly expanding area.

Functionalized Nanoporous Thin Films From Photocleavable Block Copolymers

A polystyrene-block-poly(ethylene oxide) block copolymer bearing a photocleavable junction between the blocks is used to form nanoporous thin films with carboxylic acid functions homogeneously distributed on the pore walls. The presence of the carboxylic acid groups is evidenced by fluorescence spectroscopy after their reaction with a diazomethane functionalized fluorescent dye. In addition, the initial light-responsive thin film, acting as a photoresist, can be easily patterned to selectively generate porosity in predetermined areas. In that way, fluorescent patterns can be obtained as evidenced by fluorescent microscopy.

Highly Ordered Nanoporous Thin Films from Photocleavable Block Copolymers

Poly(styrene-block-ethylene oxide) with an o-nitrobenzyl ester photocleavable junction (PS-hν-PEO) was synthesized by a combined RAFT polymerization and “click chemistry“ approach and represents the first report utilizing this method for the synthesis of photocleavable block copolymers. After solvent annealing, highly ordered thin films were prepared from PS-hν-PEO. Following a very mild UV exposure and successive washing with water, PS-hν-PEO thin films were transformed into highly ordered nanoporous thin PS films with pore diameters of 15–20 nm and long range ordering (over 2 μm × 2 μm). Afterwards the pores were filled with PDMS by spin-coating in combination with capillary forces. After treatment with oxygen plasma to remove the PS templates, highly ordered arrays of silica nanodots were obtained. This represents the first template application example from highly ordered nanoporous thin films derived from block copolymers featuring a photocleavable junction.

One is Enough: Influencing Polymer Properties with a Single Chromophoric Unit

Worth one's while: The careful use of a single chromophore on methodically designed polymers can be sufficient to modify polymer properties. Recent examples range from controlled micelle destruction and light-controlled precipitation in aqueous solution to the fabrication of nanoporous thin films (see schematic illustration of the use of a photocleavable block copolymer as a template for a nanoporous thin film).