Facile, contolled, room-temperature RAFT polymerization of N-isopropylacrylamide
ABSTRACT 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facile size exclusion chromatographic analysis of PNIPAM samples in DMF at 60 degrees C, directly on aliquots withdrawn during the polymerizations, which avoids the problems previously reported in the literature.
- SourceAvailable from: Olgun Güven
[Show abstract] [Hide abstract]
- "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. "
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.Radiation Physics and Chemistry 07/2015; 112. DOI:10.1016/j.radphyschem.2015.03.013 · 1.19 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The reversible addition−fragmentation chain transfer (RAFT) polymerization of acrylamide (AM) was studied in order to establish reaction conditions which would provide optimal rates of monomer conversion and to determine reasons for deviation of theoretical and experimental molecular weights, the former predicted from current models. To this end, chain transfer agents (CTAs) and initiators were selected and experiments performed in water and in dimethyl sulfoxide (DMSO) at specified CTA/initiator ratios and temperatures. Higher apparent rates of polymerization were achieved utilizing CTAs with higher intermediate fragmentation rates, larger initiator concentrations, and higher temperatures. For RAFT polymerization of acrylamide under these experimental conditions, a continuing supply of radicals was required in order to achieve reasonable conversions. The deviations of experimentally measured molecular weights from those theoretically predicted are a function of the CTA utilized and parallel the extent of rate retardation. The deviations are, at least in part, consistent with significant early radical coupling of stable intermediate species during the preequilibrium period (or the recently proposed CTA “initialization” period). These effects are apparent in both aqueous buffer and DMSO. The retardation effects and eventual loss of linearity of the first-order kinetic plots at extended times are also consistent with termination processes although these experiments alone do not rule out alternative mechanisms of reversible termination or slow fragmentation of intermediate species. For RAFT polymerizations in DMSO mediated by the trithiocarbonate CTA, reaction rates are significantly faster, and near quantitative conversions can be reached with proper initiator choice.Macromolecules 11/2004; 37(24). DOI:10.1021/ma048199d · 5.93 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: We report the synthesis and uses of a novel terpyridine-functionalized chain transfer agent (CTA) that produces well-controlled macromolecular architectures with terpyridine functionalities at one chain end via reversible addition−fragmentation chain transfer (RAFT) polymerization. The terpyridine-terminated macromolecules with well-defined structures were further used for preparation of supramolecular diblock metallomacromolecules by bis(2,2‘:6‘,2‘ ‘-terpyridine)ruthenium(II) complex connectivity. The successful connectivity between two macromolecular blocks via the metallocomplex was confirmed by UV−vis, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC) as well as atomic force microscopy (AFM) techniques.Macromolecules 04/2005; 38(10). DOI:10.1021/ma047955c · 5.93 Impact Factor