Doubly-Charged Ionomers with Enhanced Microphase-Separation
journal contributionposted on 08.09.2016, 13:23 by Keren Zhang, Gregory B. Fahs, Kevin J. Drummey, Robert B. Moore, Timothy E. Long
Two styrenic DABCO salt monomers allowed the synthesis of DABCO salt-containing random copolymers with two quaternized nitrogen cations on each ionic pendant group. Triethyl-(4-vinylbenzyl)ammonium chloride (VBTEACl) containing random copolymers served as singly charged controls. DABCO salt-containing copolymers with 20 mol % or lower ionic contents exhibited microphase-separated morphologies, agreeing with the multiplet-cluster model for random ionomers. Thermomechanical and morphological analyses revealed that doubly charged DABCO salts promoted more well-defined microphase-separation than singly charged analogues. Stronger ionic association of DABCO salts compared to trialkyl ammoniums resulted in superior thermomechanical and tensile properties of DABCO salt-containing ionomers. The doubly charged copolymers exhibited less water uptake per charge than the singly charged analogues. Anion exchange of the halides to more hydrophobic anions led to enhanced thermal stability, increased phase-mixing, and reduced water uptake for DABCO salt-containing copolymers and their singly charged controls. Alkyl substituent lengths on the DABCO salts affected water uptake of DABCO salt-containing copolymers. However, thermomechanical properties and thermal stability did not differ significantly between copolymers with hexyl and tetradecyl substituents.