Controlled/living radical polymerization: Features, developments, and perspectives

Monomers composed of a (meth)acrylate moiety connected to a short poly(ethylene)glycol (PEG) chain are versatile building-blocks for the preparation of “smart” biorelevant materials. Many of these monomers are commercial and can be easily polymerized by either anionic, free-radical, or controlled radical polymerization. The latter approach allows synthesis of well-defined PEG-based macromolecular architectures such as amphiphilic block copolymers, dense polymer brushes, or biohybrids. Furthermore, the resulting polymers exhibit fascinating solution properties in aqueous medium. Depending on the molecular structure of their monomer units, non linear PEG analogues can be either insoluble in water, readily soluble up to 100 °C, or thermoresponsive. Thus, these polymers can be used for building a wide variety of modern materials such as biosensors, artificial tissues, smart gels for chromatography, and drug carriers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3459–3470, 2008

Polymerization of oligo(ethylene glycol) (meth)acrylates: Toward new generations of smart biocompatible materials

3.10 - Nitroxide-Mediated Polymerization

This Perspective presents recent advances in macromolecular engineering enabled by ATRP. They include the fundamental mechanistic and synthetic features of ATRP with emphasis on various catalytic/initiation systems that use parts-per-million concentrations of Cu catalysts and can be run in environmentally friendly media, e.g., water. The roles of the major components of ATRP—monomers, initiators, catalysts, and various additives—are explained, and their reactivity and structure are correlated. The effects of media and external stimuli on polymerization rates and control are presented. Some examples of precisely controlled elements of macromolecular architecture, such as chain uniformity, composition, topology, and functionality, are discussed. Syntheses of polymers with complex architecture, various hybrids, and bioconjugates are illustrated. Examples of current and forthcoming applications of ATRP are covered. Future challenges and perspectives for macromolecular engineering by ATRP are discussed.

Macromolecular Engineering by Atom Transfer Radical Polymerization

Kinetics of Living Radical Polymerization

In nitroxide-mediated polymerization, NMP, the role of the initiation and therefore the role of the initiating dissociation rate constant kd1 on the control and livingness of a styrene and n-butyl acrylate polymerization was investigated. Different polymerizations were carried out, initiated with two different alkoxyamines based on the same nitroxide (1• or SG1). Kinetic modeling studies using the PREDICI software are used to explain these results. The use of a new tertiary SG1-based alkoxyamine 1a instead of the secondary SG1-based alkoxyamine 1b improved the control of the polymerization of both styrene and n-butyl acrylate. In particular, the polymerization of n-butyl acrylate can be carried out without adding any extra initial amount of nitroxide and the controlled polymerization of styrene at 90 °C is now possible. The complete kinetic analysis showed that the main role of the alkoxyamine with a high dissociation rate constant is to produce quickly in situ an extra amount of free nitroxide, which is ...

Nitroxide-Mediated Polymerization: The Pivotal Role of the kd Value of the Initiating Alkoxyamine and the Importance of the Experimental Conditions

The kinetics of the living radical polymerization of n-butyl acrylate (BuA) in the presence of an excess of N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (DEPN) as a rate moderator has been studied in the temperature range 115−125 °C. The equilibrium rate constant K = kd/kc between dormant and active chains was determined experimentally from the slope of ln([BuA]0/[BuA]) vs time. It obeys the following Arrhenius relation:  K = 4.93 × 105 exp(−119.3 kJ mol-1/RT), i.e., K = 1.09 × 10-10 mol L-1 at 125 °C. Some straightforward analytical kinetic equations that only depend on the excess of DEPN as the experimental parameter were established. These equations were successfully applied to simulate the DEPN-mediated polymerization of n-butyl acrylate initiated by either a styryl-DEPN alkoxyamine or an AIBN/DEPN bicomponent system. Last, the slow degradation of DEPN was considered in order to account for the upward deviation of the kinetics when a great excess of DEPN was used.

Living radical polymerization: Use of an excess of nitroxide as a rate moderator

Self-assembly of high molecular weight polydisperse acrylic block copolymers and their blends is presented under conditions as close as possible to thermodynamic equilibrium. Di- and triblock copolymers comprising a poly(butyl acrylate) (PBA) first or middle block, and poly(methyl methacrylate) (PMMA) second or outer blocks, denoted MBA and MBAM, respectively, are prepared by nitroxide-mediated polymerization (NMP). Their particularity is that the acrylic block is controlled while the methacrylate block is polymerized via an uncontrolled radical process under the synthesis conditions used. Overall composition and molecular weight polydispersities are large. Molecular disorder does not yield macrophase separation, and TEM on solvent cast films reveals lamellar and poorly ordered bicontinuous, cylindrical, or spherical morphologies. Except for the lamellar phase, clear multiple orders of diffraction are not visible in SAXS, and scattering profiles instead indicate a liquidlike order of microdomains. More im...

Molecular Disorder and Mesoscopic Order in Polydisperse Acrylic Block Copolymers Prepared by Controlled Radical Polymerization

Lack of Chain Length Effect on the Rate of Homolysis of Polystyryl-SG1 Alkoxyamines

During the last decade, Nitroxide Mediated Polymerization emerged as a promising technique to prepare controlled/living polymers via free radical polymerization. However, its scope remained limited because of the restricted number of nitroxides and alkoxyamines exhibiting the required characteristics to exert an efficient control on radical polymerization of various monomers. The combination of tertiary alkyl radicals [(Me 2 CY); Y - COOH, COOR, CN)] with the N-tert-butyl-N-(1-diethylphosphono-2,2-dimethyl-propyl) nitroxide, called SG1, led to an original series of alkoxyamines SGl-C(Y)Me 2 , some of them being isolated as stable solids easy to handle and to store. In solution, these alkoxyamines dissociate at room temperature, they exert an efficient control on the radical polymerization of various monomers and open up many new possibilities for the controlled synthesis of complex macromolecular architectures.

Florence Chauvin

Papers

Nitroxide-Mediated Polymerization: The Pivotal Role of the kd Value of the Initiating Alkoxyamine and the Importance of the Experimental Conditions

Living radical polymerization: Use of an excess of nitroxide as a rate moderator

Molecular Disorder and Mesoscopic Order in Polydisperse Acrylic Block Copolymers Prepared by Controlled Radical Polymerization

Lack of Chain Length Effect on the Rate of Homolysis of Polystyryl-SG1 Alkoxyamines

Crowded phosphonylated alkoxyamines with low dissociation temperatures : A milestone in nitroxide-mediated polymerization