Elucidation of the morphology of multi-phase blends remains a formidable challenge in material science. We have developed three new NMR methods to determine the structures and domain sizes in mixtures of ethyl cellulose (EC) and hydroxypropyl cellulose (HPC), which are important and used widely in the pharmaceutical industry, e.g., as binders or film coatings. The first method is based on proton detected spin diffusion experiments, previously used in the characterization of semicrystalline polymer morphologies. We have developed a 13C-edited mobility-filtered 1H spin diffusion experiment in which magnetization in well-defined domains is selected and its diffusion over the sample is monitored. Modelling the spin diffusion process with the diffusion equation then allows us to obtain the domain sizes of the various components in the film coatings. The second and third methods make use of alternative ways of introducing a non-equilibrium state of polarization in the solid formulation through the addition of stable radicals, so-called surface-enhanced DNP (Dynamic Nuclear Polarization) and local PRE (Paramagnetic Relaxation Enhancement). We have applied these methods to controlled release pharmaceutical formulations without the need for any advanced sample preparation. The data has helped us to fine-tune the formulation in terms of drug release characteristics and control the in vivo plasma concentration of a drug over time.

New approaches to measure domain sizes in multi-component cellulosic derivatives using NMR

253rd National Meeting (2017)

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