SYNTHESIS OF NOVEL CHITIN DERIVATIVES HAVING POLY(2-ALKYL-2-OXAZOLINE) SIDE-CHAINS

Novel chitin derivatives having poly(2-alkyl-2-oxazoline) side chains, i.e., chitin-graft-poly(2-methyl-2-oxazoline) (4a) and chitin-graft-poly(2-ethyl-2-oxazoline) (4b), were synthesized by means of the reaction of ca. 50% deacetylated chitin (3) with living poly(2-methyl-2-oxazoline) (2a) and poly(2-ethyl-2-oxazoline) (2b), respectively. The reaction between amino groups of 3 and the oxazolinium active species of 2 was examined by changing molar ratios of the feed ([2]0/[D-glucosamine units of 3]0, ranging from 1,0 to 9,9) under mild conditions (at 27-degrees-C in dimethyl sulfoxide (DMSO)). 4a having monodisperse poly(2-methyl-2-oxazoline) side chains on almost every D-glucosamine unit of the main chain was obtained in 35% yield. The number of poly(2-alkyl-2-oxazoline) side chains was roughly controlled by the molar feed ratio of 2 and 3. 4 is soluble in water, N,N-dimethylformamide, and DMSO, and partially soluble in methanol, acetonitrile, and chloroform. 4 shows improved solubilities in organic solvents, compared with 3 or chitin. The molecular motion of 4b in aqueous solution was discussed by employing H-1 NMR analytical data measured with changing temperature and solvent. In D2O and, especially, in DMSO, it is suggested that motion of the chitin backbone is restricted, compared with that of the poly(2-ethyl-2-oxazoline) side chain. The content of the side chain in 4 was calculated from the H-1 NMR spectra recorded in D2O/CD3CO2D (vol. ratio 95:5) above 60-degrees-C.