Study of the RAFT Polymerization of a Water-Soluble Bisubstituted Acrylamide Derivative. 1. Influence of the Dithioester Structure

Abstract

Homopolymers of N-acryloylmorpholine (NAM), a water-soluble bisubstituted acrylamide derivative, have been synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). Several dithioesters were used as chain transfer agents: carboxymethyl dithiobenzoate (CMDB), tert-butyl dithiobenzoate (tBDB), menthonyl dithiobenzoate (MDB), and a bifunctional dithiobenzoate, 1,3-bis(2-(thiobenzoylthio)prop-2-yl)benzene (TPB). Whereas CMDB is a commercial reagent, tBDB and MDB were synthesized by a novel biphasic process based on a thioacylation reaction and leading to very high yields. The performances of the four dithiobenzoates were compared in term of kinetics and molecular weight distribution control. Very good control of NAM polymerization was obtained with tBDB and MDB, with a linear increase of M n vs conversion over the whole conversion range and with polydispersity indices (PDI) below 1.1, as determined by aqueous size exclusion chromatography with on-line light scattering detection. In addition, a degradation phenomenon of the dithioester functions was evidenced during the course of the polymerization, correlated with a M n vs conversion curve leveling off and even sometimes decreasing above 80% conversion. Such observations were assumed to be the consequence of the formation of side products in the polymerization media, subsequently acting as nondegradative irreversible transfer agents.

A Detailed On‐Line FT/NIR and 1H NMR Spectroscopic Investigation into Factors Causing Inhibition in Xanthate‐Mediated Vinyl Acetate Polymerization

“…The outcome of a RAFT polymerization depends on the structure of thiocarbonylthio controlling agent [17][18][19][20] in conjunction with the nature of the monomer as well as on the experimental parameters. [21] Fast polymerization kinetics and excellent control of the molecular weight distribution can be achieved by favoring fast addition and fast fragmentation rates.…”

“…[34] In the context of the RAFT polymerization such transfer agents have been shown to have only limited influence on the polymerization kinetics, but can cause a leveling off and/or even a decrease in number-average molecular weights, M n , at high monomer conversions. [20] We thus believe that the observed inhibition period is more likely to be due to the presence of the by-product (B 0 ), which is more likely to react with propagating radicals to form non-propagating species.…”

“…Further, in the case of a RAFT polymerization, an additional retardation may stem from bimolecular termination reactions involving the intermediate radicals, especially if their concentration builds up. [20,32,33] In the (A)-mediated free radical polymerization of VA the O-alkyl Z-group of the xanthate sufficiently activates the C S double bond to favor addition of the highly reactive VA propagating radicals to the CTA, i.e. the ratio k add /k p between the addition rate coefficient (k add ) and the propagation rate coefficient (k p ) is sufficiently high.…”

Vinyl phenylboronic acid controlling co‐monomer for nitroxide mediated synthesis of thermoresponsive poly(2‐N morpholinoethyl methacrylate)

“…28 Another example of morpholino-functional polymers is 2-N-morpholinoethyl methacrylate (MEMA), a methacrylate related to 4AM, and unlike water-soluble 4AM homopolymers, MEMA homopolymers exhibited LCST-type behavior around 37 8C, 29 which makes MEMA an interesting candidate for polymers used in controlled release applications. Despite these properties, morpholino-functional polymers have not been as extensively studied as other thermoresponsive polymers and only recently has poly(4AM) been synthesized by controlled radical polymerizations like NMP, 25,30 RAFT, [31][32][33][34][35][36][37][38] and Cu(0)-mediated living radical polymerization (SET-LRP). 39 In this work, 4-vinylphenyl boronic acid (VPBA), was used to control the NMP of MEMA (Fig.…”

“…Using the commercially available SG1-based BlocBuilder unimolecular initiator, addition of a small amount of controlling comonomer however enables NMP methacrylic-rich copolymers (>90 mol % methacrylate) by lowering the coupled product k p K, which has been used as one measure of NMP controllability (linear M n vs. conversion, low -D, chain-end fidelity). 40 Examples of controlling co-monomers for NMP include styrene 40,41 and many of its derivatives (like sodium 4-styrene sulfonate (SS), 42 pentafluorostyrene (PFS), 32 2-vinylpyridine (2VP), 44,45 4-vinylpyridine (4VP), 46,47 9-(4-vinylbenzyl-9H-carbazole) (VBK), [48][49][50][51][52][53] and acrylonitrile (AN).…”