Functionalized Elastomeric Ionomers Used as Effective Toughening Agents for Poly(lactic acid): Enhancement in Interfacial Adhesion and Mechanical Performance

A series of elastomeric ionomers functionalized with different imidazolium-based cations were synthesized by a facile and efficient quaternization reaction from commercial bromobutyl rubber (BIIR) and different functionalized imidazoles, including 1-ethylimidazole, N-(2-hydroxyethyl)­imidazole, newly designed 1-(11′-hydroxyundecyl)­imidazole, and N-[3-(1H-imidazol-1-yl)­propyl]-hexanamide. These BIIR-based elastomeric ionomers (i-BIIRs) with a balanced mechanical performance, interfacial polar interactions, and a suitable processability were employed as novel modifying agents for poly­(lactic acid) (PLA) to achieve highly toughened sustainable blends. The influence of the cationic structure of these ionomers and blend ratio on the compatibility and mechanical performance of the blends was thoroughly investigated. The introduction of polar hydroxyl groups with varied alkyl lengths or an amide group into the imidazolium cation of the i-BIIRs markedly improved the compatibility and impact toughness of the PLA/i-BIIR blends, relative to those of the pure BIIR and the i-BIIR ionomers without functional polar groups. These PLA/i-BIIR ionomer blends exhibited an excellent flexibility–stiffness balance, in which the highest elongation at break up to 300% was achieved with a small loss in stiffness. An impressively high impact strength of 17.1 kJ/m2 was achieved for the PLA and i-BIIR-11-OH (80/20) blends, and this impact strength is almost 6 times that of the neat PLA. The interfacial adhesion between the evenly dispersed small ionomer and PLA matrix was improved because the synergistic multiple intermolecular interaction is the native mechanism for enhancing the toughness and flexibility of the blends.