I want to know how the DS is measured/calculated for a (commercially non-existing) cellulose derivative, substituted with alkyl chains. I.e. cellulose that is substituted with chort chain alkyl chains. Does anybody have an idea? Benzyl cellulose is easy with NMR, but I'm afraid that the alkyl hydrogens all end up in the same region as the Cs in the glucose unit. Am I right? Does anybody know how to solve this problem?
I think it depends on the alkyl chain, but you should be able to determinate at least CH3-groups by proton NMR (at region around 1, I think). We used that to identify alkyl chains in alkyl amine modified cellulose (http://pubs.acs.org/doi/abs/10.1021/bm500628g). We used that only as an evidence to chemical modification and we didn’t calculate exact DS by that method, however.
I think you could also try to do elemental analysis and by comparing percentages of carbon and hydrogen calculate DS when you know the molecular mass of substituent.
I am not sure I know the specific aim for deterring the DS of your alkyl cellulose. However, DS is measured to understand two things: accessibility of cellulose to reactants and steric effects of the cellulose molecule before and after reaction. Accessibility, which is depends on the tertiary structure (which in turn is influence by form-fibre, powered, film) can be measured at there levels of structural organization, namely the primary (molecular) level, secondary (cellobiose) level and tertiary (macromolecular) level. At the molecular level a measure of DS is rather a measure of molecular substitution (MS). Steric effects (conformational states) before and after reactant reacts with cellulose molecule, which depends on the activity (hinderances to or promotion of proton transfer reactions) of the C6 based on its orientation relative to the gylcosidic linkage is measure at the molecular level.
Reactivity dreaceases from C2 to C6, and then to C3. Though under certain conditions the reactivity of C6 may approach that of C2. Thus, on the basis of this reactivity discrimination, two methods come highly recommended: a comparison of the parameters of the bands associated with the O-D and O-H stretching modes after deuterium exchange with protons in unsubstituted and substituted samples as a measure of relative amounts of accessible/inaccessible OH groups and/or a measurement of moisture regain after conditioning under well-defined conditions. Here, results from Raman, Infra-red, and NMR may be complementary depending on how much time you have at your disposal.
I am thinking about measuring the DS of each glucose with MS and then doing the math. What acid do you think I should use for the hydrolysis?
can we use FTIR/GS or GPC instead of NMR for the calculation of the degree of substitution?