Catalytic Halogen Exchange in Miniemulsion ARGET ATRP: A Pathway to Well‐Controlled Block Copolymers

Abstract

Halogen exchange in atom transfer radical polymerization (ATRP) is an efficient way to chain‐extend from a less active macroinitiator (MI) to a more active monomer. This has been previously achieved by using CuCl/L in the equimolar amount to Pn−Br MI in the chain extension step. However, this approach cannot be effectively applied in systems based on regeneration of activators (ARGET ATRP), since they operate with ppm amounts of catalysts. Herein, a catalytic halogen exchange procedure is reported using a catalytic amount of Cu in miniemulsion ARGET ATRP to chain‐extend from a less active poly(n‐butyl acrylate) (PBA) MI to a more active methyl methacrylate (MMA) monomer. Influence of different reagents on the initiation efficiency and dispersity is studied. Addition of 0.1 m NaCl or tetraethylammonium chloride to ATRP of MMA initiated by methyl 2‐bromopropionate leads to high initiation efficiency and polymers with low dispersity. The optimized conditions are then employed in chain extension of PBA MI with MMA to prepare diblock and triblock copolymers.

Catalytic Halogen Exchange in Supplementary Activator and Reducing Agent Atom Transfer Radical Polymerization for the Synthesis of Block Copolymers

“…The lower activity of Cl‐capped polymers compared to Br‐capped ones is the core of the mechanism. Up to now, c HE has been reported only for e ATRP and very recently for mini‐emulsion ARGET ATRP, [ 48 ] using [Cu II TPMA] 2+ as the catalyst. With e ATRP, c HE has been successfully applied to overcome the high (re)activation rate constant of PMMA in [BMIm][OTf] and in EtOH by careful selection of suitable initiator and Cl − excess.…”

Dual electrochemical and chemical control in atom transfer radical polymerization with copper electrodes

“…39,44,45 We attempted SARA ATRP of MMA in ethanol initiated by BPN at 50 C and catalyzed by [Cu II TPMA] 2+ (TPMA ¼ tris(2-pyridilmethyl)amine), utilizing catalytic halogen exchange (cHE, with 0.05 M Bu 4 NCl) to suppress the mismatch of reactivity. 39,[46][47][48][49][50] This SARA ATRP (Table 5, entry 3) was unsuccessful, even with cHE, and resulted in a poorly controlled PMMA-Cl, with a multimodal MW distribution (M n ¼ 31.6 kDa, Đ ¼ 1.86). However, using the same conditions but superimposing electrochemical control with a potentiostatic electrolysis at E app ¼ E 1/ 2 + 0.06 V (E 1/2 ¼ À0.714 V vs. ferrocenium/ferrocene), the polymerization greatly improved (Table 5, entry 4).…”

High‐efficient surface tailoring via reverse atom transfer radical polymerization and reversible addition‐fragmentation chain‐transfer polymerization in an aqueous system initiated by a monocenter redox pair

“…The redox initiation pair consisting of hydroperoxide and ascorbic acid (AsAc) has been widely used to initiate aqueous reverse ATRP and RAFT polymerization 40,41 . The application of AsAc in the well‐controlled activator regenerated by electron transfer ATRP (ARGET ATRP) confirms that AsAc radicals could hardly initiate polymerization 42–44 . AsAc was also known to be oxidated to produce a relatively stable free radical intermediate, which provided the potential application of hydroperoxide‐AsAc redox pair in the high‐efficient surface tailoring of different materials 45…”

“…40,41 The application of AsAc in the well-controlled activator regenerated by electron transfer ATRP (ARGET ATRP) confirms that AsAc radicals could hardly initiate polymerization. [42][43][44] AsAc was also known to be oxidated to produce a relatively stable free radical intermediate, which provided the potential application of hydroperoxide-AsAc redox pair in the high-efficient surface tailoring of different materials. 45 Herein, in this work, we reported using the hydroperoxide-AsAc redox pair for the surface-initiated RAFT polymerization and reverse ATRP processes.…”