"Giant surfactants" created by the fast and efficient functionalization of a DNA tetrahedron with a temperature-responsive polymer

Copper catalyzed azide-alkyne cycloaddition (CuAAC) was employed to synthesize DNA block copolymers (DBCs) with a range of polymer blocks including temperature-responsive poly(N-isoproylacrylamide) (poly(NIPAM)) and highly hydrophobic poly(styrene). Exceptionally high yields were achieved at low DNA concentrations, in organic solvents, and in the absence of any solid support. The DNA segment of the DBC remained capable of sequence-specific hybridization: it was used to assemble a precisely defined nanostructure, a DNA tetrahedron, with pendant poly(NIPAM) segments. In the presence of an excess of poly(NIPAM) homopolymer, the tetrahedron-poly(NIPAM) conjugate nucleated the formation of large, well-defined nanoparticles at 40 °C, a temperature at which the homopolymer precipitated from solution. These composite nanoparticles were observed by dynamic light scattering and cryoTEM, and their hybrid nature was confirmed by AFM imaging. As a result of the large effective surface area of the tetrahedron, only very low concentrations of the conjugate were required in order for this surfactant-like behavior to be observed.

Multi-Functionalization of Polymers by Strain-Promoted Cycloadditions

We report here a synthetic route to oxime, azide and nitrone-bearing copolymers via reversible addition-fragmentation chain transfer copolymerization of 4-vinylbenzaldehyde and 1-(chloromethyl)-4-vinylbenzene with styrene. The azide and nitrone moieties could be employed in strain-promoted 1,3-dipolar cycloadditions with various functionalized dibenzocyclooctynols (DIBO) for metal-free post-functionalization of the polymers. In situ oxidation of the oximes with hypervalent iodine gave nitrile oxides, which could also be employed as 1,3-dipoles for facile cycloadditions with DIBO derivatives. Kinetic measurements demonstrated that the pendant nitrile oxides reacted approximately twenty times faster compared to similar cycloadditions with azides. A block copolymer, containing azide and oxime groups in segregated blocks, served as a scaffold for attachment of hydrophobic and hydrophilic moieties by sequential strain-promoted alkyne-azide and strain-promoted alkyne-nitrile oxide cycloadditions. This sequential bi-functionalization approach made it possible to prepare in a controlled manner multi-functional polymers that could self-assemble into well-defined nanostructures.

Fundamentals of RAFT Polymerization

This chapter sets out to describe the fundamental aspects of radical polymerization with reversible addition-fragmentation chain transfer (RAFT polymerization). Following a description of the mechanism we describe aspects of the kinetics of RAFT polymerization, how to select a RAFT agent to achieve optimal control over polymer molecular weight, composition and architecture, and how to avoid side reactions which might lead to retardation or inhibition.

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.

On the Origins of Nitroxide Mediated Polymerization (NMP) and Reversible Addition–Fragmentation Chain Transfer (RAFT)

The early experiments on radical polymerization, which were to lead to a study of nitroxide trapping of the initiation step and the interest in defect groups, particularly the macromonomers formed by termination by disproportionation, are discussed. Results from the nitroxide trapping clearly show that the initiation step ranges from simple clean addition to the head of the monomer, to complex addition/abstraction reactions. Careful selection of the monomer/initiation system is emphasized with particular reference to two common monomers, styrene and methyl methacrylate, and two initiating radicals, t-butoxy and benzoyloxy. The discovery of nitroxide mediated polymerization (NMP) from observations made during the nitroxide trapping work is reported and the ability to have a living radical system demonstrated with numerous examples. Similarly, the study of the copolymerization of macromonomers, formed by disproportionation of the propagating chains, is discussed with the discovery of β-scission and an early form of addition–fragmentation reported. The evolution of reversible addition–fragmentation chain transfer (RAFT) to a highly versatile and commercially attractive radical system is reported and the detailed chemistry behind the discovery of this living radical system discussed. Both NMP and RAFT enable the synthesis of structures not previously possible by radical polymerization and in some cases not possible by any other process.

Synthesis of Biodegradable Multiblock Copolymers by Click Coupling of RAFT-Generated HeterotelechelicPolyHPMA Conjugates

A new strategy for the synthesis of biodegradable high molecular weight N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymeric carriers has been designed. An enzyme-sensitive, alkyne-functionalized, chain transfer agent (CTA-GFLG-alkyne; N(α)-(4-pentynoyl)-N(δ)-(4-cyano-4-(phenylcarbonothioylthio)pentanoyl-glycylphenylalanylleucylglycyl)-lysine) was synthesized and used to mediate the reversible addition-fragmentation chain-transfer (RAFT) polymerization and copolymerization of HPMA. Post-polymerization modification with 4,4'-azobis(azidopropyl 4-cyanopentanoate)resulted in the formation of heterotelechelic HPMA copolymers containing terminal alkyne and azide groups. Chain extension via click reaction resulted in high molecular weight multiblock copolymers. Upon exposure to papain, these copolymers degraded into the initial blocks. Similar results were obtained for copolymers of HPMA with N-methacryloylglycylphenylalanylleucylglycyl thiazolidine-2-thione and N-methacryloylglycylphenylalanylleucylglycyl-gemcitabine. The new synthetic method presented permits the synthesis of biocompatible, biodegradable high molecular weight HPMA copolymer-anticancer drug conjugates that possess long-circulation times and augmented accumulation in solid tumor tissue due to the enhanced permeability and retention effect.

End Group Reactions of RAFT-Prepared (Co)Polymers

This review highlights the chemistry of thiocarbonylthio groups with an emphasis on chemistry conducted at ω or α and ω chain-ends in copolymers prepared by reversible addition–fragmentation chain-transfer (RAFT) radical polymerization. We begin by giving a general overview of reactions associated with the thiocarbonylthio groups, followed by examples associated with macromolecular thiols.