Controlled Radical Polymerization Techniques Research Articles

Solution self‐assembly of tailor‐made macromolecular building blocks prepared by controlled radical polymerization techniques

AbstractThis review describes the preparation of colloidal aggregates (spherical micelles, cylindrical micelles, polymer vesicles, multicompartment micelles, polyion complexes, schizophrenic micelles) using bottom‐up self‐assembly approaches. In particular, it focuses primarily on the self‐organization of well‐defined macromolecular building blocks (macrosurfactants, polysoaps, polyelectrolytes) synthesized by controlled radical polymerization techniques such as atom transfer radical polymerization, reversible addition fragmentation transfer polymerization and nitroxide‐mediated polymerization. The goal of this review is to highlight that these versatile techniques of polymer synthesis allow the preparation of unprecedented nanostructures in dilute solutions. Copyright © 2006 Society of Chemical Industry

Effect of Graft Chain Length and Structure Design on Temperature-Sensitive Hairy Particles

Poly(N-isopropylacrylamide) (PNIPAM) chain-grafted particle was prepared to obtain a thermosensitive microsphere. The graft polymerization of NIPAM was carried out by the controlled radical polymerization technique using an iniferter. A photosensitive iniferter was used to conduct the graft polymerization under an ambient condition (at room temperature in water). The particle diameter increased linearly with the conversion. The controllability of this reaction was examined by adding a free initiator species to the medium, and it was found that the polydispersity indices of PNIPAM generated by iniferter-control polymerization were 1.3−2.1 where number-average molecular weights were 64 000−319 000. The graft chain length affected the thermosensitivity, and the longer graft chain brought an abrupt change in diameter around 33 °C. When a small amount of acrylic acid was incorporated into the graft polymer, the particle worked as an adsorbent of protein, and its adsorbability could be controlled by the tempera...

Experimental Requirements for an Efficient Control of Free‐Radical Polymerizations via the Reversible Addition‐Fragmentation Chain Transfer (RAFT) Process

AbstractSummary: Reversible addition‐fragmentation chain transfer (RAFT) polymerization is a recent and very versatile controlled radical polymerization technique that has enabled the synthesis of a wide range of macromolecules with well‐defined structures, compositions, and functionalities. The RAFT process is based on a reversible addition‐fragmentation reaction mediated by thiocarbonylthio compounds used as chain transfer agents (CTAs). A great variety of CTAs have been designed and synthesized so far with different kinds of substituents. In this review, all of the CTAs encountered in the literature from 1998 to date are reported and classified according to several criteria : i) the structure of their substituents, ii) the various monomers that they have been polymerized with, and iii) the type of polymerization that has been performed (solution, dispersed media, surface initiated, and copolymerization). Moreover, the influence of various parameters is discussed, especially the CTA structure relative to the monomer and the experimental conditions (temperature, pressure, initiation, CTA/initiator ratio, concentration), in order to optimise the kinetics and the efficiency of the molecular‐weight‐distribution control.Schematic of the RAFT polymerization.magnified imageSchematic of the RAFT polymerization.

PP/PMMA Block Copolymers by Combination of ATRP and Metallocene Catalysis

AbstractPP‐b‐PMMA has been synthesized by a combination of metallocene catalysis and the controlled radical polymerization technique ATRP. Cp2ZrCl2/MAO and (Me4Cp)SiMe2(N‐tert‐Bu)TiCl2/MAO were used for the synthesis of atactic polypropylene. By a series of chemical modifications pp macroinitiators for the ATRP polymerization of MMA were synthesized. The PP‐b‐PMMA with polydispersities from 1.8–2.8 and an Mn ranging from 8 to 26 kg/mol was characterized by 1H‐NMR,SEC and DSC.

Microwave-assisted nitroxide-mediated polymerization of alkyl acrylates

AbstractNitroxide-mediated polymerizations of methyl and tert-butyl acrylate were performed in a single-mode microwave reactor at 120°C. The polymerizations could be carried out in a controlled way in concentrated solution (approx. 50 wt.-% of monomer) up to monomer conversions of around 90%. Monomer conversion followed first-order kinetics in the case of tert-butyl acrylate. For methyl acrylate, it seems that the kinetics obeyed the persistent radical effect. The polymers obtained from this controlled radical polymerization technique exhibited narrow molecular weight distributions (indicated by polydispersity indices below 1.3).

Polymer Protein Hybrids

AbstractStructural proteins form an important source of inspiration for materials scientists, because of the well‐defined relationship between their three‐dimensional folding pattern and their physical properties. Incorporation of structural peptide elements in synthetic polymers allows the combination of natural structural control with synthetic versatility. In this report, two approaches to introduce silk‐inspired β‐sheet elements in hybrid block copolymers are described. In our first approach we have successfully applied the controlled radical polymerization technique Atom Transfer Radical Polymerization (ATRP) to construct ABA triblock copolymers, of which the A blocks consist of PMMA and the B block consists of Ala‐Gly‐Ala‐Gly‐methacrylate moieties. This method leads to triblock copolymers with the structural peptide elements in the side chain of the middle block.Our second approach uses protein engineering for the construction of the β‐sheet element. The latter is converted into a triblock copolymer architecture by modification of both the N and C ends with poly(ethyleneglycol) chains. In this case the B block consists solely of the β‐sheet peptide element. It was demonstrated that it is possible to introduce β‐sheet characteristics in the hybrid material by means of both approaches.

Le 4 D Inonde Le Marché

Microbial infections affect humans worldwide. Many quaternary ammonium compounds have been synthesized that are not only antibacterial, but also possess antifungal, antiviral and anti-matrix metalloproteinase capabilities. Incorporation of quaternary ammonium moieties into polymers represents one of the most promising strategies for preparation of antimicrobial biomaterials. Various polymerization techniques have been employed to prepare antimicrobial surfaces with quaternary ammonium functionalities; in particular, syntheses involving controlled radical polymerization techniques enable precise control over macromolecular structure, order and functionality. Although recent publications report exciting advances in the biomedical field, some of these technological developments have also been accompanied by potential toxicological and antimicrobial resistance challenges. Recent evidenced-based data on the biomedical applications of antimicrobial quaternary ammonium-containing biomaterials that are based on randomized human clinical trials, the golden standard in contemporary medicinal science, are included in the present review. This should help increase visibility, stimulate debates and spur conversations within a wider scientific community on the implications and plausibility for future developments of quaternary ammonium-based antimicrobial biomaterials.

Chemical Tuning of the Microphase Separation in Diblock Copolymers from Controlled Radical Polymerization

We investigate whether block copolymers of controlled effective segregation strength can be designed via a novel controlled radical polymerization technique that allows statistical polymerization of different monomers in either one of the constituting blocks: We examine the morphologies and segregation regimes of two families of poly(styrene-stat-(acrylic acid))-b-poly(acrylic acid) diblocks of different block ratios (i.e., one asymmetric and one symmetric), comprising a statistical first block of variable ratio of styrene vs acrylic acid and a second PAA block. Thanks to small-angle X-ray scattering and transmission electron microscopy, we observe that as the composition of the statistical first block is varied, such asymmetric and symmetric diblocks form strongly to weakly microphase-separated structures, respectively, presenting spherical and well-ordered lamellar symmetries, or homogeneous (disordered) phases. We thus demonstrate that the segregation strength can be quantitatively controlled by the c...

Formation of Regular Honeycomb-Patterned Porous Film by Self-Organization

Regular honeycomb-structured porous films can be prepared by the casting of a polymer solution under humid conditions. The origin of these pores is `empty' water droplets, which condense from the humid atmosphere onto the solution. The water droplets self-organize into a regular array and serve as a highly regular template for the precipitating polymer. The pore size can be controlled by the casting conditions as well as by the polymer used. A spherical-shaped polymer is required to support a high regularity. These specially designed polymers can easily be prepared by controlled radical polymerization techniques.

Semiconducting Diblock Copolymers Synthesized by Means of Controlled Radical Polymerization Techniques

A donor−acceptor, rod−coil diblock copolymer has been synthesized with the objective of enhancing the photovoltaic efficiency of the PPV−C60 (PPV = poly(p-phenylenevinylene)) system by the incorporation of both components in a molecular architecture that is self-structuring through microphase separation. Diblock copolymers were obtained by using an end-functionalized rigid-rod block of poly(2,5-dioctyloxy-1,4-phenylenevinylene) as a macroinitiator for the nitroxide-mediated controlled radical polymerization of a flexible poly(styrene-stat-chloromethylstyrene) block. The latter block was subsequently functionalized with C60 through atom-transfer radical addition. In a spin-cast film of the final diblock copolymer, the luminescence from PPV is strongly quenched, indicating efficient electron transfer to C60. Under suitable conditions, solution-cast films of these diblock copolymers exhibit micrometer-scale, honeycomb-like patterns of holes.

Gradient copolymers by atom transfer radical copolymerization

Gradient copolymers, in which the instantaneous composition varies continuously along each chain, are discussed in terms of theoretical background, significance and examples from the literature. The specific focus is the use of atom transfer radical polymerization to synthesize gradient copolymers with various composition profiles. Examples of gradient copolymers using ionic and controlled radical polymerization techniques are presented. Atom transfer radical polymerization has been used under both batch and semi-batch conditions to produce gradient copolymers. The physical properties of gradient copolymers and possible future work in the field of gradient copolymers are discussed. Copyright © 2000 John Wiley & Sons, Ltd.