Modification of a Polymer Surface by Partial Swelling Using Nonsolvents

Surface modification without changing the physical properties in the bulk is of pivotal importance for the development of polymers as devices. We recently proposed a simple surface functionalization method for polymer films by partial swelling using a nonsolvent and demonstrated the incorporation of poly(2-methoxyethyl acrylate) (PMEA), which has an excellent antibiofouling ability, only into the outermost region of a poly(methyl methacrylate) (PMMA) film. We here extend this technology to another versatile polymer, polystyrene (PS). In this case, PS and PMEA have different solubility parameters making it difficult to select a suitable solvent, which is a nonsolvent for PS and a good solvent for PMEA, unlike the combination of PMMA with PMEA. Thus, such a solvent was first sought by examining the swelling behavior of PS films in contact with various alcohols. Once a mixed solvent of methanol/1-butanol (50/50 (v/v)) was chosen, PMEA chains could be successfully incorporated at the outermost region of the PS film. Atomic force microscopy in conjunction with neutron reflectivity revealed that chains of PMEA incorporated in the PS surface region were well swollen in water. This leads to an excellent ability to suppress the adhesion of platelets on the PS film.