Fast conversion of terminal thiocarbonylthio groups of RAFT polymers to “clickable” thiol groups via versatile sodium azide

Abstract

A facile and fast way of converting thiocarbonylthio end groups of RAFT polymers to thiol groups was demonstrated.

Cleavage of macromolecular RAFT chain transfer agents by sodium azide during characterization by aqueous GPC

“…Given that PX1 is unstable at room temperature, it is not surprising that significant fragmentation to PX2 appears to have occurred during MS analysis (calculated for Thiatriazoles are known to be unstable compounds in solution at room temperature and degrade into nitrogen gas, sulfur and a nitrile. [21][22][23] However, the formation of a thioacyl azide (as proposed in the work by Wu et al 14 ) instead of a thiatriazole cannot be ruled out from the above evidence since it will produce MS and NMR spectra in line with what has been observed experimentally. Importantly, it is known that the ring structure of thiatriazoles does not have an IR absorbance at 2100 -2200 cm -1 , while a thioacyl azide would since the azide absorbance at 2100 -2200 cm -1 is so strong and little altered by surrounding groups.…”

“…Note that we cannot comment quantitatively on the extent of CTA removal since there may be other groups in the polymers that absorb at CTA λ max . In order to demonstrate the general applicability of sodium azide for CTA removal and to compare these results to the work by Wu et al 14 , a second experiment studying the rate of reaction with sodium azide at higher concentrations was also conducted. Additionally, the rate of removal was compared to that which can be achieved by methylamine at identical concentrations.…”

“…As stated above, certain dithiobenzoate CTAs have already been shown to be susceptible to nucleophilic attack at high concentrations of sodium azide. 14 In the same work, a xanthate CTA was also examined and shown to have a significantly slower reaction rate than the dithiobenzoate CTA. As far as we are aware, no investigation of CTA types has thus far been conducted and so a systematic comparison of trithiocarbonates (symmetrical and standard), dithiobenzoates, xanthates and dithiocarbamates was conducted.…”

Protected thiol strategies in macromolecular design

“…The reduction to a thiol can be achieved using a nucleophile, which is typically an amine, although also hydroxides and borohydrides have been used. A recent contribution of Wu et al [165] demonstrates an alternative way of transforming the RAFT end group into a thiol, using sodium azide as nucleophile. The conversion was shown to be finished within 1 to 5 minutes, for several chain transfer agents and polymers.…”

Desulfurization–bromination: direct chain-end modification of RAFT polymers

“…25–27 For the further modification of RAFT polymers, the majority of chain-end functionalization strategies have focused on the use of the CTA as a masked thiol. 28,29 In the presence of excess nucleophiles, including amines, 23,24 azides 30 and hydrazine, 31 the CTA can be reduced to a thiol chain-end suitable for further reaction. In particular, thiol-Michael addition has been commonly reported for the introduction of a range of chain-end groups.…”