A Miscibility\nStudy of p(MMA-<i>co</i>-HEMA)-Based\nPolymer Blends by Thermal Analysis and Solid-State NMR Relaxometry

Ternary amorphous solid dispersions (ASDs) consist of\na multicomponent\ncarrier with the aim of improving physical stability or dissolution\nperformance. A polymer blend as a carrier that combines a water-insoluble\nand a water-soluble polymer may delay the drug release rate, minimizing\nthe risk of precipitation from the supersaturated state. Different\nmicrostructures of the ternary ASD may result in different drug release\nperformances; hence, understanding the phase morphology of the polymer\nblend is crucial prior to drug incorporation. The objective of this\nstudy is to investigate the miscibility of the water-insoluble p(MMA-<i>co</i>-HEMA) and water-soluble polymers such as HPC, HPMC, HPMC-AS,\nand Soluplus. To prepare the polymer blends, p(MMA-<i>co</i>-HEMA) was spray dried in 80/20 and 90/10 (w/w) ratios with one of\nthe water-soluble polymers. Thermal analysis (mDSC and DMA) and solid-state\n(ss)NMR relaxometry were applied to study the miscibility of these\nblends. No conclusions regarding miscibility could be drawn from the <i>T</i><sub>g</sub> measurements by thermal analysis. However,\nphase-separation could be demonstrated in all blends by ssNMR relaxometry.\nMoreover, by measuring both the T<sub>1ρH</sub> and T<sub>1H</sub> relaxation times, domain sizes between 5 and 50 nm could be estimated.\nThis work shows the importance of using complementary analytical techniques\nto investigate polymer miscibility.