The molecular origin of nuclear magnetic relaxation in methyl cellulose and hydroxypropylmethyl cellulose

Nuclear magnetic relaxation processes in methyl cellulose (MC) and hydroxypropylmethyl cellulose (HPMC) were studied by proton spin-lattice NMR relaxation. The proton relaxations were measured in the temperature range 90-420 K at 90 MHz. At low temperature the proton spin-lattice relaxation is caused by the modulation of the methyl proton-proton dipole-dipole interactions by the reorientation of the methyl groups. In this temperature range the spin relaxation vs. temperature data were interpreted with the model of dynamical inequivalence of methyl groups: two in MC and three in HPMC. The dynamical parameters were calculated for each of these groups. The segmental motion of the MC and HPMC chain via the glucosidic bond which corresponds to the local chain motion of these polymers is the dominant mechanism of the proton spin-lattice relaxation time above 250 K. © Springer 2005.