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Journal ArticleDOI

A New Double-Responsive Block Copolymer Synthesized via RAFT Polymerization: Poly(N-isopropylacrylamide)-block-poly(acrylic acid)

21 Sep 2004-Macromolecules (American Chemical Society)-Vol. 37, Iss: 21, pp 7861-7866
TL;DR: In this article, double-responsive block copolymers in solution were investigated by dynamic light scattering, temperature-sweep NMR, cryogenic transmission electron microscopy, and IR spectroscopy.
Abstract: Poly(N-isopropylacrylamide)-block-poly(acrylic acid), PNIPAAm-b-PAA, with low polydispersity was prepared by reversible addition−fragmentation chain transfer (RAFT) polymerization in methanol. The block copolymers respond to both temperature and pH stimuli. The behavior of the double-responsive block copolymers in solution was investigated by dynamic light scattering, temperature-sweep NMR, cryogenic transmission electron microscopy, and IR spectroscopy. The block copolymers form micelles in aqueous solutions in dependence of pH and temperature. Cloud point measurements indicated the formation of larger aggregates at pH 4.5 and temperatures above the lower critical solution temperature (LCST) of PNIPAAm. The solution behavior is strongly influenced by hydrogen bonding interactions between the NIPAAm and acrylic acid blocks.
Citations
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Journal ArticleDOI
TL;DR: A review of living radical polymerization achieved with thiocarbonylthio compounds by a mechanism of reversible addition-fragmentation chain transfer (RAFT) is presented in this article.
Abstract: This paper presents a review of living radical polymerization achieved with thiocarbonylthio compounds [ZC(=S)SR] by a mechanism of reversible addition–fragmentation chain transfer (RAFT). Since we first introduced the technique in 1998, the number of papers and patents on the RAFT process has increased exponentially as the technique has proved to be one of the most versatile for the provision of polymers of well defined architecture. The factors influencing the effectiveness of RAFT agents and outcome of RAFT polymerization are detailed. With this insight, guidelines are presented on how to conduct RAFT and choose RAFT agents to achieve particular structures. A survey is provided of the current scope and applications of the RAFT process in the synthesis of well defined homo-, gradient, diblock, triblock, and star polymers, as well as more complex architectures including microgels and polymer brushes.

2,127 citations

Journal ArticleDOI
03 Mar 2008-Polymer
TL;DR: In this paper, a review of the development of addition-fragmentation chain transfer agents and related ring-opening monomers highlighting recent innovation in these areas is presented, including dithioesters, trithiocarbonates, dithioco-baramates and xanthates.

1,309 citations

Journal ArticleDOI
TL;DR: A review of the state-of-the-art in responsive polymer systems for controlled drug delivery applications is given in this article, where the authors describe different types of stimuli-sensitive systems and give an account of their synthesis through methods such as group transfer polymerization, atom transfer radical polymerization and reversible addition-fragmentation chain transfer polymerisation.

1,186 citations

Journal ArticleDOI
TL;DR: A review of the progress made in reversible addition-fragmentation chain transfer (RAFT) and macromolecular design via the interchange of xanthates (MADIX) polymerization can be found in this article.
Abstract: Among the living radical polymerization techniques, reversible addition–fragmentation chain transfer (RAFT) and macromolecular design via the interchange of xanthates (MADIX) polymerizations appear to be the most versatile processes in terms of the reaction conditions, the variety of monomers for which polymerization can be controlled, tolerance to functionalities, and the range of polymeric architectures that can be produced. This review highlights the progress made in RAFT/MADIX polymerization since the first report in 1998. It addresses, in turn, the mechanism and kinetics of the process, examines the various components of the system, including the synthesis paths of the thiocarbonyl-thio compounds used as chain-transfer agents, and the conditions of polymerization, and gives an account of the wide range of monomers that have been successfully polymerized to date, as well as the various polymeric architectures that have been produced. In the last section, this review describes the future challenges that the process will face and shows its opening to a wider scientific community as a synthetic tool for the production of functional macromolecules and materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43:5347–5393, 2005

1,098 citations

Journal ArticleDOI
TL;DR: This review gives a brief overview about some types of stimuli-responsive nanocarriers with the main focus on organic polymer-based systems.

963 citations

References
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Journal ArticleDOI
TL;DR: Colloidal aggregates which switch reversibly can be prepared in water, and without any additive, their "inside" to the "outside", and vice versa, provide microdomains and surfaces of different character which can be controlled by a simple thermal stimulus.
Abstract: Water-soluble block copolymers were prepared from the nonionic monomer N-isopropylacrylamide (NIPA) and the zwitterionic monomer 3-[N-(3-methacrylamidopropyl)-N,N-dimethyl]ammoniopropane sulfonate (SPP) by sequential free radical polymerization via the RAFT process. Such block copolymers with two hydrophilic blocks exhibit double thermoresponsive behavior in water: the poly-NIPA block shows a lower critical solution temperature, whereas the poly-SPP block exhibits an upper critical solution temperature. Appropriate design of the block lengths leads to block copolymers which stay in solution in the full temperature range between 0 and 100 degrees C. Both blocks of these polymers dissolve in water at intermediate temperatures, whereas at high temperatures, the poly-NIPA block forms colloidal hydrophobic associates that are kept in solution by the poly-SPP block, and at low temperatures, the poly-SPP block forms colloidal polar aggregates that are kept in solution by the poly-NIPA block. In this way, colloidal aggregates which switch reversibly can be prepared in water, and without any additive, their "inside" to the "outside", and vice versa. The aggregates provide microdomains and surfaces of different character, which can be controlled by a simple thermal stimulus.

519 citations

Journal ArticleDOI
TL;DR: It is demonstrated that this bioconjugate can provide pH control of biotin binding to and triggered release from the mutant SAv, which is relevant to affinity separations, biosensors, diagnostics, enzyme processes, and targeted delivery of drugs or chemical agents, labels, and other signals.

195 citations

Journal ArticleDOI
TL;DR: This communication provides the first experimental evidence for this cooperative interaction in the acetaldehyde-CO2 complex using Raman spectroscopy at 25.0 degrees C in the gas phase.
Abstract: In carbonyl compounds having a hydrogen atom attached to the α-carbon or directly to the carbonyl carbon, our recent ab initio and solvation studies have predicted the presence of a weak C−H···O interaction with CO2. This intermolecular interaction acts cooperatively with the Lewis acid−Lewis base interaction that exists between CO2 and the carbonyl group. This communication provides the first experimental evidence for this cooperative interaction in the acetaldehyde−CO2 complex using Raman spectroscopy at 25.0 °C in the gas phase. The implications of these interactions in the solvation of carbonyl-based CO2-philes are also discussed.

122 citations

Journal ArticleDOI
TL;DR: These results are a first step in understanding alkane σ-bond metathesis on metal hydrides and are similar to those obtained with a silica-supported TaIII hydride.
Abstract: C-C activation of unactivated alkanes on a silica-supported neopentyl neopentylidene TaV complex [Eq. (1)] affords the alkane cross-metathesis products tBuCH2 R and an alkane-metathesis catalyst. Since the activity and product distributions are similar to those obtained with a silica-supported TaIII hydride, these results are a first step in understanding alkane σ-bond metathesis on metal hydrides.

97 citations

Journal ArticleDOI
TL;DR: In this paper, graft copolymers were synthesized by free radical copolymerization of AAc with PDMAAm macromonomer, and they were shown to be water-soluble at lower temperatures, while they showed a liquid−liquid phase separation from water above the characteristic transition temperatures.
Abstract: To investigate the influence of molecular architecture of poly(acrylic acid) (PAAc)-graft-poly(N,N-dimethylacrylamide) (PDMAAm) (PAAc-g-PDMAAm) on its solution properties in aqueous media, graft copolymers were synthesized by free radical copolymerization of AAc with PDMAAm macromonomer. PAAc-g-PDMAAms were water-soluble at lower temperatures, while they showed a liquid−liquid phase separation from water above the characteristic transition temperatures. The phase transition behavior was affected by the copolymer compositions and pH of the solution. Below the transition temperature, hydrogen-bonding formation between AAc and DMAAm units was observed in the PAAc-g-PDMAAm aqueous solution by FT-IR−ATR measurement. Graft copolymers were thus formed spherical associates with a diameter of ca. 150 nm estimated from the dynamic light scattering measurement. At higher temperatures, the dehydrated regions and the weak dehydration of the PDMAAm chains induced cooperatively the hydrophobic aggregation, resulting in ...

86 citations