Facile, Controlled, Room-Temperature RAFT Polymerization of N -Isopropylacrylamide †
Department of Polymer Science, University of Southern Mississippi, Hattiesburg, Mississippi 39406, USA. Biomacromolecules
(Impact Factor: 5.75).
07/2004; 5(4):1177-80. DOI: 10.1021/bm049825h
Poly(N-isopropyl acrylamide) is a thermoresponsive polymer that has been widely investigated for drug delivery. Herein, we report conditions facilitating the controlled, room-temperature RAFT polymerization of N-isopropylacrylamide (NIPAM). The key to success is the appropriate choice of both a suitable RAFT chain transfer agent (CTA) and initiating species. We show that the use of 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid, a trithiocarbonate RAFT CTA, in conjunction with the room-temperature azo initiator 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), in DMF, at 25 degrees C, yields conditions leading to NIPAM homopolymerizations which bear all of the characteristics of a controlled/"living" polymerization. We also demonstrate facile size exclusion chromatographic analysis of PNIPAM samples in DMF at 60 degrees C, directly on aliquots withdrawn during the polymerizations, which avoids the problems previously reported in the literature.
Available from: Olgun Güven
- "observed that the use of the trithiocarbonate DMPA in conjunction with V-70 allowed for the synthesis of PNIPAM in a controlled fashion (Convertine et al., 2004). In our study, we also found that PNiPAAm had a narrow molecular weight distribution when synthesized in the presence of DMPA by gamma radiation. "
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ABSTRACT: Poly(N-isopropylacrylamide) (PNiPAAm) is synthesized by gamma radiation induced Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization. The monomer is polymerized in the presence of two different trithiocarbonate-based RAFT agents i.e., Cyanomethyldodecyltrithiocarbonate (CDTC) and 2-(Dodecylthiocarbonothioylthio)-2-methylpropionic acid (DMPA) in dimethylformamide (DMF) at room temperature under nitrogen atmosphere. Number-average molecular weights (Mn) and dispersities of the polymers were determined by Size Exclusion Chromatography (SEC). Dispersities (Ɖ) of the resulting polymers are narrow, i.e., Ɖ≤1.18, indicating the occurrence of well-controlled polymerization via radiation induced RAFT process. %Conversion is determined by gravimetric method and also confirmed by Proton Nuclear Magnetic Resonance (1H-NMR) Spectroscopy. By selecting proper [Monomer]/[RAFT] ratio and controlling conversion it is possible to synthesize PNiPAAm in the molecular weight range of 2400–72400 with extremely low molecular weight distributions with the anticipation of preparing corresponding size-controlled nanogels. The phase transition of PNiPAAm with low dispersity synthesized by RAFT is sharper than PNiPAAm synthesized by free radical polymerization.
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ABSTRACT: A water-soluble diblock copolymer was prepared from sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS) and N-isopropylacrylamide (NIPAM) via reversible addition−fragmentation chain transfer (RAFT) controlled radical polymerization. The RAFT “living” radical polymerization process of NIPAM using an NaAMPS-based macrochain transfer agent was confirmed by the fact that the number-average molecular weight increased linearly with monomer consumption while the molecular weight distribution remained to be narrow for the polymerization. The NIPAM block exhibited a lower critical solution temperature (LCST) in water. Both the NaAMPS and NIPAM blocks are soluble in water at room temperature. At temperatures above the LCST, the NIPAM blocks associated into a polymer aggregate. The polymer aggregate was assumed to be an elongated micelle or a multiple aggregate due to intermicellar association of the spherical core−corona micelles based on characterization data obtained from 1H NMR, turbidity, light scattering, and fluorescence probe experiments. A hydrophobic compound such as 8-anilino-1-naphthalenesulfonic acid, ammonium salt hydrate (ANS), was incorporated into the hydrophobic aggregate of the NIPAM blocks above LCST and released from the aggregate when temperature was reduced below LCST. The capture and release of ANS triggered by temperature change were completely reversible.
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