Disclosed are thermoplastic compositions comprising partially or fully neutralized carboxylic acid-based ionomers modified with rosin or rosin derivatives and, optionally, organic acids and salts thereof. Methods of preparing the thermoplastic compositions are also provided. The thermoplastic compositions exhibit higher hardness and stiffness than typical ionomer compositions. Also disclosed are golf balls, sporting equipment, and other non-sport articles comprising said thermoplastic compositions and methods for their preparation.