In some embodiments, a polymer film includes a base composition of poly(ethylene-vinyl acetate) and a surface composition comprising hydroxy groups. In some embodiments, a polymer film includes a base layer of a first composition of poly(ethylene-vinyl acetate), a surface layer at a surface of the base layer, and a coating layer of a second composition of a copolymer of glycerol and sebacic acid. The surface layer includes surface hydroxy groups converted from acetate groups of the poly(ethylene-vinyl acetate). The second composition is attached to the surface layer by ester bonds between carboxyl groups of the copolymer and the hydroxy groups. A single-use bioreactor bag includes a polymer film including a base composition of poly(ethylene-vinyl acetate) and a surface composition comprising hydroxy groups. A method of modifying a poly(ethylene-vinyl acetate) film includes converting acetate groups at a first surface of the poly(ethylene-vinyl acetate) film to hydroxy groups.