Reversible Deactivation Radical Polymerization Research Articles

Highly Defined Multiblock Copolypeptoids: Pushing the Limits of Living Nucleophilic Ring‐Opening Polymerization

Advanced macromolecular engineering requires excellent control over the polymerization reaction. Living polymerization methods are notoriously sensitive to impurities, which makes a practical realization of such control very challenging. Reversible-deactivation radical polymerization methods are typically more robust, but have other limitations. Here, we demonstrate by repeated (≥10 times) chain extension the extraordinary robustness of the living nucleophilic ring-opening polymerization of N-substituted glycine N-carboxyanhydrides, which yields polypeptoids. We observe essentially quantitative end-group fidelity under experimental conditions that are comparatively easily managed. This is employed to synthesize a pentablock quinquiespolymer with high definition.

One-Step Synthesis of Amphiphilic, Double Thermoresponsive Diblock Copolymers

The copolymerization of an excess of a functionalized styrene monomer, 4-vinylbenzyl methoxytetrakis(oxyethylene) ether, with various N-substituted maleimides yields tapered diblock copolymers in a one-step procedure, when applying reversible deactivation radical polymerization (RDRP) methods, such as ATRP and RAFT. The particular chemical structure of the diblock copolymers prepared results in reversible temperature-responsive two-step aggregation behavior in dilute aqueous solution. In this way, a double hydrophilic block copolymer is transformed step by step into an amphiphilic macrosurfactant, and finally into a double hydrophobic copolymer, as followed by turbidimetry and dynamic light scattering. Copolymers in which the maleimide repeat units bear short hydrophobic side chains are freely water-soluble at low temperature and form micellar aggregates above their cloud point. Further heating above the phase transition temperature of the second block results in secondary aggregation. Copolymers with maleimides that bear strongly hydrophobic substituents undergo two thermally induced aggregation steps upon heating, too, but show in addition intramolecular hydrophobic association in water already at low temperatures, similar to the behavior of polysoaps.

Aqueous RAFT/MADIX polymerisation of vinylphosphonic acid

RAFT/MADIX polymerisation of vinylphosphonic acid (VPA) was controlled in water with an O-ethyl xanthate transfer agent. This represents the first example of reversible deactivation radical polymerisation of a monomer bearing an unprotected phosphonic acid function. Hence, macromolecular engineering of polyphosphonates can now be envisioned by directly polymerising VPA in water.

Reversible-deactivation radical polymerization mediated by CuSO4·5H2O: an alternative and promising copper(ii)-based catalyst

This work demonstrated a successful example of RDRP with CuSO4·5H2O as a Cu(II) based catalyst in the presence of a reducing agent. CuSO4·5H2O produced a more controllable polymerization compared with the widely used CuBr2. The mechanism was revealed to be a Cu(0)-mediated RDRP with the in situ generated Cu(0) from CuSO4·5H2O as the catalyst. This work may provide an alternative, economical and promising copper(II)-based RDRP catalyst, which would eventually enrich and benefit the RDRP technique.

Threshold Particle Diameters in Miniemulsion Reversible-Deactivation Radical Polymerization

Various types of controlled/living radical polymerizations, or using the IUPAC recommended term, reversible-deactivation radical polymerization (RDRP), conducted inside nano-sized reaction loci are considered in a unified manner, based on the polymerization rate expression, Rp = kp[M]K[Interm]/[Trap]. Unique miniemulsion polymerization kinetics of RDRP are elucidated on the basis of the following two factors: (1) A high single molecule concentration in a nano-sized particle; and (2) a significant statistical concentration variation among particles. The characteristic particle diameters below which the polymerization rate start to deviate significantly (1) from the corresponding bulk polymerization, and (2) from the estimate using the average concentrations, can be estimated by using simple equations. For stable-radical-mediated polymerization (SRMP) and atom-transfer radical polymerization (ATRP), an acceleration window is predicted for the particle diameter range, . For reversible-addition-fragmentation chain-transfer polymerization (RAFT), degenerative-transfer radical polymerization (DTRP) and also for the conventional nonliving radical polymerization, a significant rate increase occurs for . On the other hand, for the polymerization rate is suppressed because of a large statistical variation of monomer concentration among particles.

The Impact of Band Broadening on Molar‐Mass Determination of Narrow‐Distribution Polymer by Size‐Exclusion Chromatography

AbstractA systematic study of the effects of band broadening (BB) in size‐exclusion chromatography (SEC) on Poisson molar‐mass distributions (MMDs) is carried out. Such distributions apply for polymer standards used for SEC calibration, and they are a good model for the MMD from any quasi‐living polymerization, including reversible‐deactivation radical polymerization (RDRP). BB is simulated using the exponentially modified Gaussian model, which is shown to work excellently for actual polymer standards. A series of simulations with this model revealed how BB parameter values affect number‐average degree of polymerization and polydispersity index from SEC. It is shown that the skewness parameter is particularly important in these considerations. Many of the obtained trends echo ones from RDRP, suggesting that BB has been making a hitherto unsuspected – indeed uninvestigated – contribution to deviations from ideal behavior in such systems.magnified image

RAFT Polymerization and Thiol Chemistry: A Complementary Pairing for Implementing Modern Macromolecular Design

Reversible addition fragmentation chain transfer (RAFT) polymerization is one of the most extensively studied reversible deactivation radical polymerization methods for the production of well-defined polymers. After polymerization, the RAFT agent end-group can easily be converted into a thiol, opening manifold opportunities for thiol modification reactions. This review is focused both on the introduction of functional end-groups using well-established methods, such as thiol-ene chemistry, as well as on creating bio-cleavable disulfide linkages via disulfide exchange reactions. We demonstrate that thiol modification is a highly attractive and efficient chemistry for modifying RAFT polymers.

Synthetic Strategies for the Design of Peptide/Polymer Conjugates

We review the advantages and drawbacks of the various synthetic strategies for conjugating peptides to synthetic polymers obtained from reversible-deactivation radical polymerization (also known as living radical polymerization, controlled radical polymerization, or controlled/living radical polymerization). By using a selection of examples, we summarize the concept behind divergent and convergent syntheses, which lead to the production of linear and grafted peptide/polymer conjugates. In the second section of this review, we present an overview of a near–universal convergent approach for the production of peptide/polymer conjugates, by combining reversible addition–fragmentation chain transfer (RAFT) polymerization and copper(I)–catalyzed Huisgen 1,3-dipolar cycloaddition reactions between an azide and an alkyne (CuAAC).

Nitroxide-Mediated Radical Polymerization: Limitations and Versatility

Since its introduction in the early 1990s, nitroxide-mediated radical polymerization (NMP) has been widely adopted for the preparation of a panoply of new polymer architectures. While NMP provides a number of advantages for the preparation of specific types of polymers, several inherent limitations with NMP have led to the more widespread use of other reversible-deactivation radical polymerization (RDRP) methods, chiefly atom transfer radical polymerization (ATRP) and reversible addition-fragmentation-chain transfer (RAFT) polymerization, in polymer synthesis. This short review discusses strategies that have been adopted for dealing with the difficulties of NMP and also surveys the use of NMP to prepare new polymers and copolymers over the past several years.

Synthesis of double-hydrophilic poly(methylacrylic acid)-poly(ethylene glycol)-poly(methylacrylic acid) triblock copolymers and their micelle formation

The aim of the work reported was to synthesize a series of double-hydrophilic poly(methacrylic acid)-block-poly(ethylene glycol)-block-poly(methacrylic acid) (PMAA-b-PEG-b-PMAA) triblock copolymers and to study their self-assembly behavior. These copolymeric self-assembly systems are expected to be potential candidates for applications as carriers of hydrophilic drugs. Bromo-terminated difunctional PEG macroinitiators were used to synthesize well-defined triblock copolymers of poly(tert-butyl methacrylate)-block-poly(ethylene glycol)-block-poly(tert-butyl methacrylate) via reversible-deactivation radical polymerization. After the removal of the tert-butyl group by hydrolysis, double-hydrophilic PMAA-b-PEG-b-PMAA triblock copolymers were obtained. pH-sensitive spherical micelles with a core–corona structure were fabricated by self-assembly of the double-hydrophilic PMAA-b-PEG-b-PMAA triblock copolymers at lower solution pH. Transmission electron microscopy and laser light scattering studies showed the micelles were of nanometric scale with narrow size distribution. Solution pH and micelle concentration strongly influenced the hydrodynamic radius of the spherical micelles (48–310 nm). A possible reason for the formation of the micelles is proposed. Copyright © 2010 Society of Chemical Industry

Terminology for reversible-deactivation radical polymerization previously called "controlled" radical or "living" radical polymerization (IUPAC Recommendations 2010)

This document defines terms related to modern methods of radical polymerization, in which certain additives react reversibly with the radicals, thus enabling the reactions to take on much of the character of living polymerizations, even though some termination inevitably takes place. In recent technical literature, these reactions have often been loosely referred to as, inter alia, "controlled", "controlled/living", or "living" polymerizations. The use of these terms is discouraged. The use of "controlled" is permitted as long as the type of control is defined at its first occurrence, but the full name that is recommended for these polymerizations is "reversible-deactivation radical polymerization".

Living Radical Polymerization by the RAFT Process - A Second Update

This paper provides a second update to the review of reversible deactivation radical polymerization achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition–fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379–410). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669–692). This review cites over 500 papers that appeared during the period mid-2006 to mid-2009 covering various aspects of RAFT polymerization ranging from reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses and a diverse range of applications. Significant developments have occurred, particularly in the areas of novel RAFT agents, techniques for end-group removal and transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.

Living Radical Polymerization by the RAFT Process – A Third Update

This paper provides a third update to the review of reversible deactivation radical polymerization (RDRP) achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669) and the second in December 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymerization which include reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.