Benzyl and Cumyl Dithiocarbamates as Chain Transfer Agents in the RAFT Polymerization of N-Isopropylacrylamide. In Situ FT-NIR and MALDI−TOF MS Investigation

The principles of RAFT polymerization were applied to the polymerization of N-isopropylacrylamide (NIPAAm), which was carried out in the presence of the dithiocarbamates benzyl 1-pyrrolecarbodithioate and cumyl 1-pyrrolecarbodithioate, respectively, as chain transfer agents in 1,4-dioxane at 60 °C. A kinetic investigation using in situ FT-NIR spectroscopy shows very long induction periods which depend on the nature and concentration of the chain transfer agent. The resulting polymers have polydispersity indices Mw/Mn < 1.3 and have been investigated by MALDI−TOF mass spectrometry, GPC, NMR, and UV spectroscopy. The expected end group signals for chain transfer agent (CTA) and initiator could be identified together with fragmentation of the dithioester end group under MALDI conditions. The number-average molecular weights obtained by MALDI−TOF MS are significantly lower than those obtained by GPC with polystyrene calibration. With the use of the abovementioned dithiocarbamates, new thiocarbonylthio compounds have been applied in the RAFT polymerization of N-isopropylacrylamide.