Universal (Switchable) RAFT Agents

Abstract

The polymerization of most monomers that are polymerizable by radical polymerization can be controlled by the reversible addition-fragmentation chain transfer (RAFT) process. However, it is usually required that the RAFT agent be selected according to the types of monomer being polymerized. Thus, RAFT agents (dithioesters, trithiocarbonates) suitable for controlling polymerization of "more activated" monomers (MAMs; e.g., styrene, acrylates, methacrylates, etc.) tend to inhibit polymerization of "less activated" monomers (LAMs; e.g., vinyl acetate, N-vinylpyrrolidone, etc.). Similarly RAFT agents suitable for polymerizations of LAMs (xanthates, certain dithiocarbamates) tend to give little or poor control over polymerizations of MAMs. We now report a new class of "switchable" RAFT agents, N-(4-pyridinyl)-N-methyldithiocarbamates, that provide excellent control over polymerization of LAMs and, after addition of 1 equiv of a protic or Lewis acid, become effective in controlling polymerization of MAMs, allowing the synthesis of poly(MAM)-block-poly(LAM) with narrow molecular weight distributions.

Living Radical Polymerization by the RAFT Process - A Second Update

“…B See footnote B of Table 3. 261 [416] BA [416] (BA) [416] VAc [416] 262 [416] NVP [416] NVC [416] MA [416] St [416] (NVC) [416] MA-b-NVC [416 MMA [416] MMA-b-VAc [416] C A See footnote A of Table 3. B See footnote B of Table 3.…”

“…[416] N-(4-pyridinyl)-N-methyldithiocarbamates (Table 14) are effective with LAMs and in the presence of a strong acid, the protonated form of the N-(4-pyridinyl)-Nmethyldithiocarbamates provide excellent control over the polymerization of MAMs. [416] The process is illustrated in Scheme 4 for the preparation of poly(methyl methacrylate)-block-PVAc.…”

“…[416] N-(4-pyridinyl)-N-methyldithiocarbamates (Table 14) are effective with LAMs and in the presence of a strong acid, the protonated form of the N-(4-pyridinyl)-Nmethyldithiocarbamates provide excellent control over the polymerization of MAMs. [416] The process is illustrated in Scheme 4 for the preparation of poly(methyl methacrylate)-block-PVAc. Thus in the first step the protonated RAFT agent (formed by adding 4-toluenesulfonic acid) is used to control the polymerization of MMA to form PMMA.This macro-RAFT agent is then neutralized in situ by adding a stoichiometric amount of N,Ndimethylaminopyridine (DMAP).…”

RAFT Polymerization of Vinyl Esters: Synthesis and Applications

“…The N-pyridyl dithiocarbamates discussed above are also known as switchable RAFT agents [42], as protonation of the pyridyl group results in the formation of a RAFT agent of comparable activity to a dithioester or trithiocarbonate. In their protonated form, these dithiocarbamates are capable of controlling the polymerization of more activated monomers such as acrylates and S, but inhibit the polymerization of vinyl esters and N-vinyl monomers such as N-vinyl carbazole [42].…”

“…While high molar mass PVAc samples with low dispersities are accessible by CoMRP, this technique is applicable only to a narrow range of monomers, which hampers its development. In contrast, RAFT technology using xanthates and dithiocarbamates [41,42] is of particular interest for its ease of application, versatility and compatibility with a large range of monomers with very different reactivities including vinyl esters.…”