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°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 1 H NMR analytical data measured with changing temperature and solvent. In D 2 O 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 1 H NMR spectra recorded in D 2 O/CD 3 CO 2 D (vol. ratio 95:5) above 60°C.