Polymer Structure and Property Effects on Solid Dispersions with Haloperidol: Poly(N-vinyl Pyrrolidone) and Poly(2-oxazolines) Studies

Poly(2-methyl-2-oxazoline) (PMOZ), poly(2-propyl-2-oxazoline) (PnPOZ) and poly(2-isopropyl-2-oxazoline) (PiPOZ) were synthesized by hydrolysis of 50 kDa poly(2-ethyl-2-oxazoline) (PEOZ) and subsequent reaction of the resulting poly(ethylene imine) with acetic, butyric and isobutyric anhydrides, respectively. These polymers were characterized by proton nuclear magnetic resonance, FTIR spectroscopy, powder X-ray diffraction, and differential scanning calorimetry. The poly(2-oxazolines) as well as poly(N-vinyl pyrrolidone) (PVP) were used to prepare solid dispersions with haloperidol, a model poorly soluble drug. Dispersions were investigated by powder X-ray diffractometry, differential scanning calorimetry and FTIR spectroscopy. Increasing the number of hydrophobic groups (-CH- and -CH) in the polymer resulted in greater inhibition of crystallinity of haloperidol in the order: PVP > PnPOZ = PEOZ > PMOZ. Interestingly, drug crystallization inhibition by PiPOZ was lower than with its isomeric PnPOZ because of the semi-crystalline nature of the former polymer. Crystallization inhibition was consistent with drug dissolution studies using these solid dispersions, with exception of PnPOZ, which exhibited lower critical solution temperature that affected the release of haloperidol.