Living Radical Polymerization with Alkali and Alkaline Earth Metal Iodides as Catalysts

Abstract

The generation of an alkyl radical (R•) from an alkyl iodide (R–I) with NaI playing a catalytic role was experimentally demonstrated. This catalytic reaction was exploited as an activation process for living radical polymerization. Alkali metal iodides, NaI, KI, and CsI, and alkaline earth metal iodides, MgI2 and CaI2, were systematically studied as catalysts. 18-crown-6-Ether and a polyether, that is, diethylene glycol dimethyl ether (diglyme), were utilized to solvate these catalysts in hydrophobic monomers. Among the five catalysts, NaI exhibited a particularly high reactivity. The polymer molecular weight and its distribution (M w/M n = 1.2−1.4) were well controlled with high conversions (e.g., 80–90%) in reasonably short periods of time (3–6 h) at mild temperatures (60–70 °C) in the polymerizations of methyl methacrylate. NaI is also amenable to styrene, acrylonitrile, and functional methacrylates. In addition to homopolymers, NaI also afforded well-defined block copolymers, chain-end functional polymers, and a star polymer. The high monomer versatility and accessibility to a wide range of polymer architectural designs are desirable features of this polymerization system.

Low‐Temperature, Rapid Copolymerization of Acrylic Acid and Sodium Acrylate in Water

“…S3 and Table , entry 1–2). These results suggest that NaI may directly moderate polymer growth or enhance the efficiency of chain transfer to iodoacetonitrile, in accordance with recent reports indicating reversible complexation of NaI with active alkyl iodides moderates the polymerization of methyl methacrylate.…”

“…This strategy, inspired by reports on controlled iodine chain‐transfer systems from Goto and Matyjaszewski, benefits from radical processes that are well‐known in organic synthesis and are most efficient for alkyl iodides . We postulate that the elementary reactions of polymerization (initiation, propagation, and termination) can be supplemented with degenerative chain transfer events to yield an iodine‐capped dormant species that limits side reactions and lowers both molar mass and dispersity via a reduction in the number of active radicals …”

Schiff base as a novel kind of catalyst for reversible complexation‐mediated radical polymerization of methyl methacrylate

“…Moreover, the dosage of NDBE is lower than that commonly used in reported RCMP system ([CP‐I] 0 :[catalyst] 0 = 1:0.5) . In our system, the molar ratio of [CP‐I] 0 :[NDBE] 0 = 1:0.125 can also realize RCMP of MMA with obvious “living” features.…”

“…The M n,GPC agreed with the theoretical value, and the PDI was Moreover, the dosage of NDBE is lower than that commonly used in reported RCMP system ([CP-I] 0 :[catalyst] 0 = 1:0.5). 31,36,41 In our system, the molar ratio of [CP-I] 0 :[NDBE] 0 = 1:0.125 can also realize RCMP of MMA with obvious "living" features. All these characters showed the high efficiency of NDBE as a catalyst for RCMP of MMA.…”

“…Organic salts (including tetrabutylammonium iodine (BNI) and ethylmethylimidazolium iodide) were a class of high effective organic catalysts for RCMP, and high‐molecular‐weight polymers (up to M n = 140,000 g mol −1 ) with narrow distribution were obtained. Other reported RCMP catalysts include organic superbases (such as guanidine with conjugated three‐nitrogen framework), alkaline earth metal iodides (such as NaI), choline iodide analogues (including choline iodide and butyrylcholine iodide), and azide anion (such as NaN 3 ) . At the same time, photocontrolled LRP has been achieved using iodine as capping agent .…”