A composition includes an esterified styrene/maleic anhydride copolymer, where the esterified styrene/maleic anhydride copolymer contains the following copolymerized components: (a) styrenic component; (b) a dicarboxylic acid ring-opened maleic anhydride; and (c) a half ester of a ring-opened maleic anhydride where the ester is a product of reacting maleic anhydride with poly(ethylene glycol) methyl ether having a number-average molecular weight in a range of 100 to 800 grams per mole, where the molar ratio of component (c) to component (b) is greater than 0.5 as determined by nuclear magnetic resonance spectroscopy, and the molar ratio of component (a) to the sum of components (b) and (c) is 1.0 or more and 2.0 or less as determined by nuclear magnetic resonance spectroscopy.
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