Elsevier

Polymer

Volume 44, Issue 22, October 2003, Pages 6761-6765
Polymer

Polymer Communication
The direct polymerization of 2-methacryloxyethyl glucoside via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization

https://doi.org/10.1016/j.polymer.2003.08.039Get rights and content

Abstract

A preliminary study on the direct controlled radical polymerization of a glycomonomer, namely 2-methacryloxyethyl glucoside (MAGlu), under reversible addition-fragmentation chain transfer (RAFT) polymerization conditions in aqueous media has been conducted. This represents the first example detailing the direct polymerization of a sugar monomer via RAFT and, significantly, has been conducted without protecting group chemistry. 4-Cyano-4-methyl-4-thiobenzoylsulfanyl butyric acid (CTP) was employed as the RAFT chain transfer agent (CTA) due to its inherent water-solubility and its applicability for methacrylic monomers. The homopolymerization displays all the characteristics of a controlled/‘living’ polymerization—linear increase in Mn with conversion, pseudo-first order kinetics, the final polymers have narrow molecular distributions and novel block copolymers can be prepared.

Introduction

In recent years there has been increasing interest in (co)polymers bearing sugar moieties—so called ‘glycopolymers’—due in part to their biomimetic properties [1]. Synthetic glycopolymers may be synthesized via two broad methods: (1) the polymerization of sugar-bearing monomers and (2) the post-polymerization modification of preformed polymers with sugar-containing reagents. The polymerization of glycomonomers has been reported by a wide variety of techniques such as traditional free radical, [2] ring-opening, [3], [4] anionic, [5] coordination, [6] cationic, [7], [8] stable free radical, [9], [10], [11] and atom transfer radical [12], [13] polymerization (ATRP) methods. However, with only a few exceptions, notably hydrogels prepared by traditional free radical polymerization, certain statistical copolymers prepared by cyanoxyl-mediated polymerizations, and a recent report detailing the polymerization of 2-gluconamidoethyl methacrylate via ATRP, the above techniques have typically employed the use of protected glycomonomers for successful polymerization, followed by selective deprotection.

Clearly, the ability to directly polymerize glycomonomers without the need for protecting group chemistry is beneficial. To this end, we recently examined reversible addition-fragmentation chain transfer (RAFT) [14] polymerization as a possible candidate for accomplishing this. RAFT has proven to be an extremely versatile controlled free radical polymerization (CRP) technique, applicable to a wide range of monomers, [15], [16], [17] functionality, [17], [18], [19], [20], [21] and conditions, [22], [23], [24], [25], [26], [27], [28], [29] and importantly is also readily conducted in aqueous media [30]. For example, historically ‘problematic’ monomers such as acrylamido [17], [20], [31], [32], [33], [34], [35], [36], [37], [38] derivatives are generally readily polymerized in a controlled fashion under RAFT conditions in both aqueous and non-aqueous media. Herein, we report preliminary observations for the direct polymerization of 2-methacryloxyethyl glucoside (MAGlu) directly in aqueous media without the use of protecting group chemistries, see Scheme 1.

Section snippets

Materials

MAGlu was purchased from Polysciences Inc. as a 50 wt% aqueous solution (mixture of anomers) and was purified by passage over a column of basic alumina. The azo initiator, V-501, was a gift from Wako and was recrystallized from methanol prior to use. 4-Cyano-4-methyl-4-thiobenzoylsulfanyl butyric acid (CTP) was prepared according to the method previously reported [21].

Homopolymerization of MAGlu

To a 20 ml scintillation vial equipped with a magnetic stir bar was added MAGlu (as a 50 wt% solution, 2.53 g, 1.71 M) and CTP

Homopolymerization of MAGlu

The direct polymerization of the glycomonomer MAGlu in aqueous media via RAFT has been attempted using CTP as the RAFT CTA, and V-501 as the azo initiator. CTP was chosen for its inherent water-solubility and the fact that cyanoalkyl derivatives of dithiobenzoates are particularly effective for the controlled polymerization of methacrylates [39]. Fig. 1 shows the experimentally determined molecular weight (MW) distributions with increasing conversion for a polyMAGlu (PMAGlu) homopolymer.

It is

Concluding remarks

Herein we have reported preliminary observations regarding the aqueous RAFT polymerization of MAGlu, without the need for protecting group chemistries, at 70 °C employing CTP as the RAFT CTA. The homopolymerization displays the characteristics of a controlled/living polymerization although deviations from the theoretical MW are observed at higher conversions. Also, we have shown that it is possible to produce novel sugar-based AB-diblock copolymers in which MAGlu may be polymerized first or

Acknowledgements

ABL wishes to thank the Chair of the Department of Chemistry and Biochemistry, the Dean of the College of Science and Technology and the VP for Research at the University of Southern Mississippi for generous start-up funds.

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    Present address: Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA.

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