Abstract
Studies on the end group stability of poly(N-isopropylacrylamide) during the atom transfer radical polymerization (ATRP) process are presented. Polymerization of N-isopropylacrylamide was conducted in different solvents using a copper(I) chloride/Me6Tren catalyst complex. The influence of the ATRP solvent as well as the polymer purification process on the end group stability was investigated. For the first time, mass spectrometry results clearly underline the loss of ω end groups via an intramolecular cyclization reaction. Furthermore, an ATRP system based on a copper(I) bromide/Me6Tren catalyst complex was introduced, that showed not only good control over the polymerization process, but also provided the opportunity of block copolymerization of N-isopropylacrylamide with acrylates and other N-substituted acrylamides. The polymers were characterized using 1H-NMR spectroscopy and size exclusion chromatography. Polymer end groups were determined via ESI-TOF mass spectrometry enhanced by ion mobility separation (IMS).
Highlights
The development of controlled radical polymerization (CRP) techniques in the early 1990s enabled the synthesis of polymers with advanced architecture [1,2,3,4]
If the addition of the second monomer was done after 120 min, the resulting copolymer showed a relatively high number of inactive PNIPAAm chains leading to a significant shoulder in the molecular mass distribution. These results indicated that the halide end groups of the PNIPAAm homopolymers were not stable for more than 1 h in the atom transfer radical polymerization (ATRP) reaction mixture
End group stability of PNIPAAm homopolymers prepared by copper-catalyzed ATRP was investigated using electrospray ionization (ESI)-ion mobility separation (IMS)-TOF mass spectrometry and size exclusion chromatography (SEC)
Summary
The development of controlled radical polymerization (CRP) techniques in the early 1990s enabled the synthesis of polymers with advanced architecture [1,2,3,4]. The first-order kinetic plots were reported to be linear in the case of water/DMF (v/v 1:1) but showed significant curvature for ATRP of NIPAAm in DMSO, ethanol, 2-propanol, and tert-butyl alcohol [22,24] This deviation from a first-order kinetic was attributed to a partial oxidation of the copper(I)-complex, especially at the beginning of the reaction. We describe our studies on end group stability of ATRP-synthesized PNIPAAm. The CuCl/Me6 Tren catalyst complex was used in different solvents (water/DMF, DMSO, acetonitrile) with methyl-2-chloropropionate (MCP) as initiator. A new bromine-based ATRP system is presented, allowing the controlled polymerization of NIPAAm and the block copolymer synthesis of NIPAAm with acrylates and acrylamides. Different strategies are explained of how to remove residual amounts of unreacted macroinitiator after block copolymer synthesis
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