In this article

effects of ion content

counterion

ionic group

short-range chain-structure (flexibility

permittivity

group steric-hindrance

branching

covalent cross-linking

etc.) of the matrix polymer

degree of neutralization

ionic-group distribution along the backbone chain

ambient conditions (temperature

solvent

water

etc.)

and preparation history (melt pressing

solution casting

re-precipitation

high-temperature annealing

etc.) on the ion-aggregation morphology (fraction of aggregated ionic-groups

shape

size

aggregation number

number density

distribution-in-matrix and internal coordination structure of ionic aggregates) have systematically been reviewed for ionomers. On the basis of this

it has been pointed out that four basic issues on ion-aggregation morphology are urgent to be resolved

i.e.

whether there exists an ordered arrangement of atoms inside the ionic aggregates

origin of the low-temperature differential scanning calorimetry (DSC) endothermic peak of ionomers

disadvantages of the currently-held ion-hopping theory

and effect of molecular weight

an important index to long-range chain-structure of the matrix polymer

on the ionic-aggregate morphology. Particularly

it has been suggested that

to extend and perfect the ion-hopping theory

we accommodate two morphological factors

ionic-aggregate aggregation number (i.e.

extent of chain-segment close packing in the coronas of ionic aggregates) and number density (i.e.

ionic cross-linking density)

in addition to the pre-existing structural factor

strength of ionic interactions

thereby to reasonably explain or predict the structure-property relationships of ionomers.