This paper introduces the synthesis, characterization, surface properties, and reactions of maleic acid monoester end group functionalized polymers. Acylation using maleic acid anhydride of hydroxyl end groups present in either poly(ethylene glycol) (PEG) or poly(trimethylene carbonate) (PTMC) afforded the corresponding maleic acid monoester salts (PEGDM) or (PTMCM). Michael additions of ethanethiol or cysteine to the conjugated double bonds were performed in solution or at a polymer film-water interface. To further evaluate the reactivity and regioselectivity of the thiol addition to maleic acid monoester, a model compound, benzyl 6-hydroxyhexanoate, was used to aid a spectroscopic characterization. Film properties, evaluated with contact angle measurements, of PTMCM revealed surface-active properties of ionic maleic acid monoester salt. Further contact angle measurements showed that maleic acid monoesters present at the polymer-water interface could be reacted with the mercapto group in cysteine to give an amino acid decorated surface.