Ionomer

An ionomer (iono- + -mer) is a <a href="/facts/Polymer/eF32E50K">polymer</a> composed of repeat units of both <a href="/facts/Electric_charge/xxsBfmlB">electrically</a> neutral repeating units and <a href="/facts/Ion/3bePpDna">ionized</a> units covalently bonded to the polymer backbone as <a href="/facts/Pendant_group/5UBRDNDC">pendant group</a> <a href="/facts/Functional_group/GXkSPsjM">moieties</a>. Usually no more than 15 <a href="/facts/Mole_percent/nW4EepmJ">mole percent</a> are ionized. The ionized units are often carboxylic acid groups.
The classification of a polymer as an ionomer depends on the level of substitution of ionic groups as well as how the ionic groups are incorporated into the polymer structure. For example, <a href="/facts/Polyelectrolyte/3A3jLXkh">polyelectrolytes</a> also have ionic groups covalently bonded to the polymer backbone, but have a much higher ionic group molar substitution level (usually greater than 80%); ionenes are polymers where ionic groups are part of the actual polymer backbone. These two classes of ionic-group-containing polymers have vastly different morphological and physical properties and are therefore not considered ionomers. 
Ionomers have unique physical properties including <a href="/facts/Electrical_conductivity/akyCKvMy">electrical conductivity</a> and viscosity—increase in ionomer solution viscosity with increasing temperatures (see <a href="/facts/Conducting_polymer/JbwFx9IL">conducting polymer</a>). Ionomers also have unique morphological properties as the non-polar polymer backbone is energetically incompatible with the polar ionic groups. As a result, the ionic groups in most ionomers will undergo <a href="/facts/Microphase_separation/35D97DuV">microphase separation</a> to form ionic-rich domains.
Commercial applications for ionomers include <a href="/facts/Golf_ball/1r2Y3CEb">golf ball</a> covers, <a href="/facts/Semipermeable_membrane/YxENKzn5">semipermeable membranes</a>, sealing tape and <a href="/facts/Thermoplastic_elastomer/bBGfjapB">thermoplastic elastomers</a>. Common examples of ionomers include <a href="/facts/Polystyrene_sulfonate/wfgeTdAh">polystyrene sulfonate</a>, <a href="/facts/Nafion/Lnhpg5WM">Nafion</a> and Hycar.

Ionomer open-in-new

Ionomer