Development of hot-melt extrusion as a novel technique for the ...

Fig. 6.6b: 1 H NMR spectra of all PRP and DPD formulations.To investigate the potential interactions found within the drug/polymer formulation,1 H NMR inverse recovery experiments were carried out to analyse spin relaxation times [31,32] . Differing relaxation rates of nuclear spins can be related to aspects of molecular structureand additionally to internal molecular motion. The rationale of these experiments was to lookat potential changes of the drugs molecular motion, before and after HME processing. Indeed,it would be assumed that the free drug (with a low molecular weight) would have quite a highmolecular motion leading to fairly high T 1 relaxation delays. After extrusion, any possibleinteractions between the drug and polymer would result in a decrease in the amount ofmolecular motion observed for the drug. T 1 relaxation times are particularly sensitive tointermediate molecular motions which result in short T 1 s. Molecules which have fast or slowmolecular motion can have comparable T 1 s (Supp. Fig. 5-8).In Table 6.4, significant changes (p>0.05) between the T 1 relaxation times for thedrugs and the drug/polymer solutions can be observed. It is expected that low molecularweight present relatively fast molecular motion in solution. The decrease in T 1 of the extrudeddrug – polymer blends indicates a slowing in the molecular motion of the compounds. Thisresult would infer that there is some type of molecular interaction between the drugs andpolymers in methanol solutions, although the proximity of the interactions cannot beelucidated.123 | P a g e