Mucoadhesive films are attractive for buccal drug delivery because of their extended retention on the mucosal surface, enabling sustained drug delivery to and across the tissue. In this study, poly(2-hydroxyethyl ethyleneimine) (P2HEEI) was synthesized by reacting linear polyethyleneimine (L-PEI) with 2-bromoethanol and combined with chitosan to formulate mucoadhesive films for buccal delivery of haloperidol. The polymer displayed excellent solubility in water, a low glass transition temperature (-31.6 °C) and low toxicity in human dermal skin fibroblast cells. This polymer was then blended with chitosan before films were formed by a casting technique. Differential scanning calorimetry and scanning electron microscopy confirmed that chitosan and P2HEEI were fully miscible in the blends. The films based on chitosan-P2HEEI blends were more elastic and had enhanced mechanical properties. Films containing haloperidol were also formulated. The release of haloperidol from the films increased as the P2HEEI content in the blends was raised. Mucoadhesion of these films on ex vivo sheep buccal mucosal tissues was evaluated using a tensile method. All films were mucoadhesive but increasing P2HEEI content in the blend gradually reduced adhesion to the buccal mucosa.