Synthesis and characterisation of regioselective cellulose derivatives
The typical regioselective cellulose derivatives 3-mono-O-alkyl cellulose samples bearing two different ether moieties, namely methyl/ethyl, methyl/n-propyl, and ethyl/n-propyl were synthesized applying protecting group technique. The NMR spectra of the peracetylated products revealed the regioselectivity of the alkylation as well as the degree of substitution of both alkyl moieties. The number average degree of polymerization (DPn) calculated from size exclusion chromatography decreases from DPn 117 (starting cellulose, Avicel PH-101) to DPn range of 20-50 due to the multi-step synthesis. It could be demonstrated that the lower critical solution temperature (LCST) is influenced by the degree of substitution of both alkyl groups. For example, LCST values between 33 and 58°C were measured for aqueous solutions of 3-mono-O-ethyl/n-propyl cellulose. On the contrary, the solution behaviour of a mixture of 3-mono-O-ethyl- and 3-mono-O-propyl cellulose, e. g., was controlled by the derivative with the lowest LCST.