RAFT Synthesis of a Thermally Responsive ABC Triblock Copolymer Incorporating N-Acryloxysuccinimide for Facile In Situ Formation of Shell Cross-Linked Micelles In Aqueous Media

A poly(ethylene oxide) (PEO)-based macromolecular chain transfer agent (macro-CTA) was employed to demonstrate the controlled polymerization of N,N-dii-nethylacrylamide (DMA) in anhydrous 1,4-dioxane at 70 degrees C using reversible addition-fragmentation chain transfer polymerization. This macro-CTA was then used to mediate the statistical copolymerization of DMA and the reactive monomer N-acryloxysuccinimide (NAS), forming a diblock copolymer of PEO-b-(DMA-s-NAS). Subsequent chain extension with N-isopropylacrylamide (NIPAM) yielded a PEO-b-(DMA-s-NAS)-b-NIPAM thermally responsive triblock copolymer. In aqueous solution at room temperature the triblock copolymer chains exist as unimers but form micelles when the solution temperature is raised above the lower critical solution temperature (LCST) of the NIPAM block. The hydrodynamic dimensions and micellization temperatures depend on the length of the NIPAM block. Incorporation of the NAS units into the triblock copolymer allows for facile formation of uniform shell cross-linked micelles by reaction with difunctional primary amines in aqueous media. These shell cross-linked micelles swell when the solution temperature is lower than the LCST of the NIPAM block

Reversible Addition Fragmentation Chain Transfer Polymerization of Water-Soluble, Ion-Containing Monomers

Reversible add ition-fragmentation chain transfer (RAFT) polymerization has been the focus of extensive research over the last several years. RAFT allows for the tailoring of polymers with complex architectures including block, graft, comb, and star structures with predetermined molecular weights, end group functionality, and narrow molecular weight distributions. In this chapter we present an overview of the synthesis and solution properties of water-soluble, ioncontaining monomers synthesized via RAFT

RAFT-synthesized Diblock and Triblock Copolymers: Thermally-Induced Supramolecular Assembly in Aqueous Media

This review highlights recent advances in the synthesis of functional, temperature-responsive, water-soluble block copolymers, including particular focus on the results obtained by employing reversible addition-fragmentation chain transfer ( RAFT) polymerization. The applicability of the RAFT process for the polymerization of functional monomers under a diverse range of experimental conditions has facilitated the synthesis of water-soluble (co) polymers that were previously inaccessible. Unprecedented control afforded by RAFT in homogeneous aqueous media allows well-defined polymeric systems to be prepared without stringent purification techniques and under increasingly ``green\u27\u27 conditions while maintaining the ability to tailor many of the macromolecular characteristics ( molecular weight, chain topology, copolymer composition, functionality, etc.) that affect self-assembly in solution. Block copolymer formation and postpolymerization modification utilizing crosslinking and copper-catalyzed azide-alkyne click\u27\u27 chemistry are described, with attention being paid to their ability to control copolymer structure for subsequent self-assembly in response to changes in temperature

Responsive Nanoassemblies Via Interpolyelectrolyte Complexation of Amphiphilic Block Copolymer Micelles

Shell locked nanoassemblies ranging in size from 34 to 78 nm have been prepared from interpolyelectrolyte complexation of block copolymer micelles of poly[(N,N-dimethylacrylamide)-b-(N-acryloylalanine)-b-(N- isopropylacrylamide)] with the homopolymer poly(ar-vinylbenzyl)trimethylammonium chloride above the unimer to micelle phase transition temperature of the block copolymer in water. Of technological significance is the reversibility of the shell cross-linking by addition of 0.4 M NaCl, allowing micelle dissociation below the lower critical solution temperature of the copolymer micelles. Poly(N-acryloylalanine) (AAL) and block copolymers were prepared directly in water via controlled reversible addition fragmentation chain transfer (RAFT) polymerization utilizing mono- and difunctional poly(N,N-dimethylacrylamide) macroCTAs

Aqueous RAFT Polymerization of Acrylamide and N,N-Dimethylacrylamide at Room Temperature

The first example of a room temperature reversible addition fragmentation chain transfer polymerization conducted directly in aqueous media is detailed. Under these conditions acrylamide and N,N-dimethylacrylamide may be polymerized in a controlled fashion to near quantitative conversions employing a difunctional trithio-carbonate chain transfer agent (CTA). Hydrolysis studies conducted at pH 5.5 suggest that the CTA is stable up to approximately 50 degrees C

Aqueous RAFT Polymerization of Acrylamide and N,N-Dimethylacrylamide At Room Temperature

The first example of a room temperature reversible addition-fragmentation chain transfer polymerization conducted directly in aqueous media is detailed. Under these conditions acrylamide and N,N-dimethylacrylamide may be polymerized in a controlled fashion to near quantitative conversions employing a difunctional trithiocarbonate chain transfer agent (CTA). Hydrolysis studies conducted at pH 5.5 suggest that the CTA is stable up to approximately 50°C

Chiroptical Properties of Homopolymers and Block Copolymers Synthesized From the Enantiomeric Monomers \u3ci\u3eN\u3c/i\u3e-acryloyl-L-alanine and \u3ci\u3eN\u3c/i\u3e-acryloyl-D-alanine Using Aqueous RAFT Polymerization

Chiral homo- and block copolymers based on the enantiomeric monomers N-acryloyl-l-alanine (ALAL) and N-acryloyl-d-alanine (ADAL) were prepared directly in water using controlled reversible addition–fragmentation chain transfer (RAFT) polymerization. The polymerization of the chiral monomers proceeded in a controlled fashion producing the respective homopolymers, block copolymers, and a statistical copolymer with targeted molecular weights and narrow molecular weight distributions. The chiroptical activity of these biomimetic polymers and their analogous model compounds was investigated using circular dichroism (CD). P(ALAL) and P(ADAL) were shown to be optically active exhibiting mirror image CD spectra. In addition, statistical and enantiomeric block copolymers prepared at 1:1 stochiometric ratios exhibited virtually no optical activity