Sugar-based monomers

Synthetic polymers obtained from sugar-based monomers are innocuous for human health. Their hydrophilic nature ensures a greater hydrolytic degradability [6], and reduces their environmental impact compared to classic polymers [3]. 

Some reviews have been published on the synthetic carbohydrate-based polymers and glycopolymers [11-15]. However, they refer mainly to poly(vinylsaccharide)s and other conventional functionalized polymers having sugars as groups pendant from the main chain of the polymer. In this chapter we shall describe those sugar-based monomers which lead to polymers having the sugar units incorporated into... 

The ADMET polymerization of sugar-based monomers is much less explored than the ROMP approach, and only a few examples have been reported to date. Bui and Hudlicky prepared a,oo-dienes derived from a biocatalytically synthesized diene diol, from which chiral polymers (up to 20 kDa) with D-c/uro-inositol units were prepared via ADMET in the presence of 1 mol% of C4 [169]. Furthermore, several ot,co-dienes containing D-mannitol, D-ribose, D-isomannide, and D-isosorbide have been synthesized by Enholm and Mondal [170]. Also in this study, C4 was used to catalyze the ADMET polymerizations at 1 mol% catalyst loading. As pointed out by the authors, the viscosity increased as the reactions progressed and vacuum had to be applied to efficiently remove the released ethylene. Unfortunately, the polymers obtained were not further analyzed. As already mentioned above, Fokou and Meier have also reported the ADMET polymerization of a fatty acid-/D-isosorbide-based a,co-diene [126]. Furthermore, Krausz et al. have synthesized plastic films with good mechanical properties by cross-linking fatty esters of cellulose in the presence of C3 [171-173]. 

Sustained efforts have been extensively devoted to prepare new polymers based on renewable resources and with higher degradability. Of the different natural sources, carbohydrates stand out as highly convenient raw materials because they are inexpensive, readily available, and provide great stereochemical diversity. This chapter describes the potential of sugar-based monomers as precursors to a wide variety of macromolecular materials, with particular emphasis on both the mechanisms of polymerization and the properties of the ensuing products. 

Sugar-based monomers. Carbohydrate monomers. Bifunctional sugar derivatives. Alditols, Aminosugars, Aldonic acids, Aldaric acids... 

Scheme 4 Free-radical copolymerization of an exo-cyclic unsaturated sugar-based monomers (type ll). ...

The complete elimination of functional groups is often an undesirable side reaction in organic synthesis, but on the other hand it is a possibility for the recycling of environmentally harmful compounds, for example phenols and haloarenes such as polychlorinated dibenzodioxins (PCDDs or dioxins ). For example, aryl chlorides can be effectively dechlorinated with Pd(0) NPs in tetra-butylammonium salts with almost quantitative conversions also after 19 runs (entry H, Table 1.4) [96]. On the other hand, a C-0 bond cleavage reaction also seems suitable for the fragmentation of sugar-based biomass such as cellulose or cello-biose in that way, sugar monomers and bioalcohol can be derived from renewable resources (entry F, Table 1.4) [164]. 

From the results presented in this chapter we can conclude that it is feasible to prepare sugar-based polymers analogous to the more qualified technological polymers - polyamides, polyesters, polyurethanes - with an enhanced hydrophilicity and degradability. However, in most cases, the high costs associated with the preparation of the monomers restrict the application of these polymers to biomedical applications and other specialized fields. More readily available monomers and simpler polymerization processes have to be found if sugar-derived polymers should compete with petrochemical-based polymers that are used in domestic applications. 

The above sections provide information about the synthesis of block copolymers using CRP techniques. In the first section, details about the nitroxide-based systems were presented. From the literature reports, it is clear that TEMPO and TEMPO-based analogs only produce block copolymers of St-based monomers successfully. Liquid crystalline monomers, sugar containing derivatives, and even silicon-based St monomers were successfully homopolymerized. Water soluble monomers like sodium 4-styrenesulfonate and 4-(dimethylamino) methylstyrene were successfully incorporated into block copolymers using TEMPO in aqueous media. However, there was evidence that even with some St derivatives, particularly those that were chloromethylated, side reactions occurred to pro-... 

Wulff et alr attached vinyl groups to a large chiral sugar based template molecule and then copolymerized this substrate wdth various monomers. With MMA and MAN they achieved some optical induction. This approach lias been extended in studies of higher molecular weight systems. "" Thus, PVA was esterilied with methacryloyl chloride to give a "multimethacrylate" (24) and... 

An entirely different approach to sugar-based polymers involves the use of selective enzymatic catalysts to prepare vinyl sugar monomers that are subsequently polymerized via chemical catalysts. Tokiwa and Kitagawa (25) published extensively on this subject, and their contribution within this book describes a wide range of sugar monomer structures. 

Lactic acid (LA) is one of the top carbohydrate-derived chemicals and it was recently included in BozeU and Petersen s revised selecticai of the top ten sugar-based chemicals [10, 24]. The conversion of carbohydrates into LA via anaerobic fermentation has been known for ages [25]. The first industrial fermentation was developed by A. Boehringer in 1895 and at the present time the global installed production capacity is estimated at 0.5 Mton year [10, 26, 27]. The current fermentation process and its issues will be critically discussed in Sect. 3 in light of the major application of LA today, i.e., as monomer for commercial bioplastic PLA [28]. Besides being used for polyester synthesis, LA is seriously considered as a platform chemical for the synthesis of a diverse range of chemicals such as pyruvic acid, 2,3-pentanedione, and acrylic acid [10, 29]. 

In comparison to nucleic add or peptide chemistry, the chemistry of carbohydrates remains relatively difficult and challenging. In this context, the direct polymerization of monomers bearing monosaccharide or oligosaccharide moieties is a very convenient method for preparing sugar-based macromolecules. This particular aspect has been comprehensively described in an excellent recent review of Ladmiral et Thus, the following section presents only a concise overview of this field of research and highlights principally recent examples. 

Sugar-based fatty acid ester diols have also been prepared by transesterification of epoxidised oleates with methyl a-D-glucopyranoside and sucrose, followed by hydrolysis of the oxirane ring [57]. These fully bio-based monomers were polymerised with an aliphatic diisocyanate to produce PU whose structure could be oriented toward a linear architecture (when the sugar OH groups were not involved) or a network (if at least some of them participated in the polycondensation) by changing the solvent medium. 

The fine understanding of copolymerization mechanisms should be extended using the same methodology to the microstructural study of copolymers with more complex structure such as sugar-based copolymers as well as polymer networks from multifunctional monomers. 

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