Current-controlled ‘plug-and-play’ electrochemical atom transfer radical polymerization of acrylamides in water

Abstract

Aqueous electrochemical atom transfer radical polymerisation (eATRP) can be challenging due to deleterious side reactions leading to the loss of the ω-chain end, increased rates of activation (k_act) leading to higher [P_n˙], increased rates of termination, and the lability of the X–Cu^II/L bond to hydrolysis leading to poor control. Herein, we build on recent advances in eATRP methodology to develop a simplified current-controlled eATRP of acrylamides in water. The simplification arises from the use of commercial, standardised reaction hardware which enables the polymerisations to be performed in a 2-electrode, ‘plug-and-play’, undivided electrochemical cell configuration. Further simplification is afforded by the design of a single stepwise current profile (I_appvs. time) capable of mediating current-controlled eATRP of N-hydroethylacrylamide (HEAm). At room temperature, polymerisation of HEAm to target degrees of polymerisation (DP_n,th) of 20–100 proceeds with good control (Đ ≤ 1.50). Loss of control when targeting higher DP_n at room temperature is circumvented by lowering the reaction temperature (RT to 0 °C), increasing the stirring rate (400 rpm to 800 rpm) and increasing the catalyst concentration. Using the best conditions, a linear increase in M_n,SEC with DP_n (up to DP_n = 320) and low dispersity values (DP_n,th = 40–160; Đ = 1.26–1.38) were obtained. Furthermore, the current profile and reaction conditions can support the polymerisation of other primary and secondary acrylamides and the retention of the ω-Br chain end is exemplified by a short in situ chain extension. Overall, this represents further simplification of aqueous eATRP with respect to reaction set up and experimental parameters (single current profile) which has been employed to synthesise polyacrylamides with good efficiency and control.