Chain Transfer Kinetics of Acid/Base Switchable N-Aryl-N-Pyridyl Dithiocarbamate RAFT Agents in Methyl Acrylate, N-Vinylcarbazole and Vinyl Acetate Polymerization

Abstract

The structures of the 'Z' and 'R' substituents of a RAFT agent (Z-SCS2-R) determine a RAFT agent's ability to control radical polymerization. In this paper we report new acid/base switchable N-aryl-Npyridyl dithiocarbamates (R= -CH2CN, Z = -N(Py)(Ar)) which vary in substituent at the 4-position of the aryl ring and the use of these to control molecular weight and dispersity. In their protonated form, the new RAFT agents are more effective in controlling polymerization of the more activated monomer, methyl acrylate (MA), whereas in their neutral form they provide more effective control of the polymerization of less activated monomers, N-vinyl carbazole (NVC) and vinyl acetate (VAc). For each polymerization, the apparent chain transfer coefficient (Ctr app ) shows a good correlation with Hammett parameters. Dithiocarbamates with more electron-withdrawing aryl ring substituents have the higher Ctr app . This demonstrates the influence of polar effects on Ctr app and supports the hypothesis that the Scheme 1: Canonical Structures of dithiocarbamates 2 3Recently, we have reported acid/base switchable RAFT agents (4, R'=CH3) which possess a pyridyl moiety capable of moderating the electron density, and hence reactivity, of the thiocarbonyl group (see Scheme 2). [14][15][16] The pyridinium species 5 allows for control over the polymerization of MAMs, whilst the neutral species 4 controls the polymerization of LAMs. Factors that affect the acid/base equilibria and hence the extent of protonation of the RAFT agent in solution have a marked effect on the dispersity of the polymers obtained during MAM polymerization. 16 Importantly, the switchable RAFT protocol also allows for the preparation of block copolymers incorporating both MAM and LAM monomer units (i.e.poly(MAM)-block-poly(LAM)) [14][15][16] which are generally unobtainable using the conventional RAFT methodology.Scheme 2: Acid/base switchable RAFT agents 4 5 Herein, we show that new acid/base "switchable" N-aryl-N-pyridyl dithiocarbamates of structure 4, where R' is aryl or pyridyl, possess enhanced activity in both the acidified and neutral forms when compared to that of the parent class (R' = CH3). These specific RAFT agents (4) were synthesized as the incorporation of aryl substituents as R', due to their electron withdrawing character, should enhance their activity and improve control over molar mass (Mn) and dispersity (Đ). We also demonstrate how manipulation of the RAFT agent structure influences chain transfer kinetics during homopolymerization of methyl acrylate

Functionalisation of MWCNTs with poly(lauryl acrylate) polymerised by Cu(0)-mediated and RAFT methods

“…16,48 Initially, lauryl acrylate was polymerised using RAFT (Scheme 2) and Cu(0) mediated polymerisation (Scheme 3).…”

RAFT Polymerization of Vinyl Esters: Synthesis and Applications

“…In between these extremes, a wide range of R-groups may be employed to good effect, including esters of 1-acetyl [86][87][88][89][90]108,[110][111][112][113], 2-propionyl [3][4][5][6][7][8][9]30,31,34,66,69,70,[80][81][82]85,89,91,107,[114][115][116][117][118][119][120][121][122][123] and 2-methyl-2-propionyl [67,91], 2-acetic acid [124], 2-propionic acid [106,114,125], t-butyl [106], cyanomethyl [67,102], benzyl …”

“…Polymerizations of VAc have been carried out in the presence of a series of N-aryl N-(4-pyridyl) S-cyanomethyl dithiocarbamates with substituents of varying electron-withdrawing ability [102]. In contrast to the trend observed with xanthates [86], the apparent chain transfer constant of the RAFT agent increased with the electron-withdrawing nature of the substituent, from 93 for N-(p-methoxyphenyl) N-pyridyl S-cyanomethyl xanthate to over 320 for N-(4-pyridyl) N-(p-cyanophenyl) S-cyanomethyl dithiocarbamate.…”

Living Radical Polymerization by the RAFT Process – A Third Update

“…[115] Activity, as indicated by a higher C tr app or a lower for the polymer formed, increases with the electron-withdrawing qualities of Ar-X. Some retardation was also observed with the more active RAFT agents of this class.…”

“…Their analysis indicates a low value for K of ,10 1 M À1 (608C). As pointed [115] A See text for definitions of kinetic parameters and the section Abbreviations for the definitions of the abbreviations used here. out by Junkers et al [131] the more than six orders of magnitude difference in K for these two systems appears surprising.…”