Here, a lower value of χdp (ideally = 0) suggests a better polymer-drug compatibility. For χdp calculation (equation no. 7), the total solubility parameters (δT) of drug and polymer is needed. As noted previously, the YMB method gave the similar δT values (for PrOzi and PentOx polymer) (Table ) and molar volume values (for BuOx and PrOzi polymer) i.e. 20.8 MPa 1/2 and 145.60 cm 3 /mol, respectively (Figure ). This already gave a hint that Flory-Huggins interaction parameter would not be an appropriate method to estimate the compatibility, because of the same δT and molar volume values. Therefore, the measurement of Ra (equation no. 8), which involves the utilization of individual δd, δp, δh values was only considered for compatibility estimation. The smaller distance between polymers and drugs in Hansen space represent the higher compatibility. Importantly, Ra of the two substances in the Hansen space only provide the qualitative information of compatibility.