Characterization of polymer‐brush‐type polysaccharide β‐ketoesters

Abstract

Polyvinyl alcohol (PVA) and four glucans, cellulose, curdlan, amylase, and pullulan, were dissolved in 8% lithium chloride/1,3-dimethyl-2-imidazolodinone, and reacted with ketene dimers with long alkyl or alkenyl chains under homogeneous conditions. The corresponding polysaccharide b-ketoesters with degrees of substitution (DS) of 2.1-2.9 and the PVA b-ketoester with DS 0.9 were prepared in the yields of 80-90%. Solution-state 1 H-and 13 C-NMR spectra of the polysaccharide and PVA b-ketoesters revealed that the polymer chains behaved like solid even in solutions. However, size-exclusion chromatographic analysis showed that the polysaccharide and PVA b-ketoesters prepared had random-coil conformations in tetrahydrofuran, which could not explain the anomalous NMR patterns. The specific chemical structures of the substituents having long and branched alkyl or alkenyl chains may have brought about such specific solution-state NMR patterns, irrespective of the chemical structures of the polymer backbones.

Structural analysis of polymer-brush-type cellulose β-ketoesters by molecular dynamics simulation

“…Thus, the 1 H-and 13 C-NMR spectra of the cellulose b-ketoesters look like simple alkanes or alkenes, and no information concerning DS, DS distribution among the C2, C3 and C6 hydroxyls of cellulose or others could be obtained from their NMR spectra. Such anomalous NMR patterns were observed also for polysaccharide b-ketoesters with DS 2.3-2.9 prepared from pullulan, amylose and curdlan (Yoshida and Isogai 2008). Moreover, a polyvinyl alcohol b-ketoester with DS 0.9 also showed similar NMR patterns.…”

Cyclic alkyl ketene oligomers

“…These solutionstate 13 C-NMR spectra of AKOs are very similar to those of polymer-brush-type cellulose b-ketoesters with degrees of substitution of >2 prepared from cellulose via homogeneous reaction with AKDs. [4][5][6][7] In the case of the polymer-brush-type cellulose bketoesters, cellulose molecules and b-ketoester parts (except long alkyl chains) behave like solid even in solution state owing to strong restriction in their mobility via the densely introduced long alkyl chains into cellulose molecules. [4][5][6][7] The results of solution-state 13 C-NMR spectra of AKOs also indicated that the connection parts of the repeating units were strongly restricted in mobility.…”

“…[4][5][6][7] In the case of the polymer-brush-type cellulose bketoesters, cellulose molecules and b-ketoester parts (except long alkyl chains) behave like solid even in solution state owing to strong restriction in their mobility via the densely introduced long alkyl chains into cellulose molecules. [4][5][6][7] The results of solution-state 13 C-NMR spectra of AKOs also indicated that the connection parts of the repeating units were strongly restricted in mobility. If AKOs have linear chemical structures consisting of the repeating units, some carbon signals due to both ends of oligomer chains should be detected in the 13 C-NMR spectra.…”

“…2 Yoshida et al have prepared cellulose b-ketoesters with degrees of substitution of >2 by reactions of cellulose (dissolved in a non-aqueous cellulose solvent) with various AKDs (prepared form C12-C18 fatty acid chlorides) in the presence of 1-methylimidazole used as an esterification promoter. [4][5][6][7] The obtained polymer-brush-type cellulose derivatives had unique properties; carbons of cellulose chains and those close to the b-ketoester bonds behave like solids in solution states, because mobility of these carbons are strongly restricted even in solution states, owing to the long alkyl chains densely introduced to cellulose chains. Moreover, it was found that significant amounts of AKOs were formed as by-products from AKDs in the reaction mixtures, and that the formation of these AKOs disturbed efficient b-ketoesterification between cellulose and AKDs.…”

“…Moreover, it was found that significant amounts of AKOs were formed as by-products from AKDs in the reaction mixtures, and that the formation of these AKOs disturbed efficient b-ketoesterification between cellulose and AKDs. [4][5][6][7] Thus, according to the literature and our previous studies, two protocols are possible to prepare AKOs, AKO-I and AKO-II. AKO-I is formed as a by-product during AKD synthesis and present as a contaminant in the obtained AKD wax, and AKO-II is formed from AKD during b-ketoesterification of cellulose in the presence of 1-methylimidazole.…”