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Ionomer |
Ionomers are polymer with ethylene as the major component but contains both covalent and ionic bonds in their chemical structure. The covalent bond generally exist within the elements of the chain while the ionic bonds are formed between the chains. They are made up of both non-ionic repeat units and a small amount (about 15%) of ion containing repeat units.
Ionomer, as its name suggests, is an ion that contains polymer, or you may simply call it a polymer ion. An Ion, as we all know, is a charged atom that contains either positive or negative charge on it. An ionomer is a special kind of Polyelectrolyte (old polymer with ionic groups). They are also popular as Copolymer, which contains small amount of ion containing repeat units and nonionic repeat units.
Ionomers are a type of thermoplastic called reversible crosslinker. In an ionomer, the nonpolar chains are are in the same group while the ionic groups are tightly joined to the polymer chain. For this reason thermoplastic ionomers tend to act like crosslinked polymers or block copolymers. The ionic group in the chain loses their mutual attraction on being heated and the chains start to move around freely. This increases with the increase in temperature till a point when the groups cannot stay in their cluster anymore. This allows the polymer to act as an elastromer.
Ionomers - Crossed Linked Polymers or Not??
Ionomers are not crossed linked polymers, but still are a kind of thermoplastic called reversible cross-linker. It is because of their heating property.
Physical Property:
When heated, the ionic groups lose their attractions and the chains begin to move freely. With an increase in temperature, the chains start moving faster and as a result the group clusters break. This makes it a polymer with the properties of an elastomer and the process ability of a thermoplastic. These ionomers are sometimes known as thermoplastic elastomers.
Commercial Applications:
- Golf Ball Covers
- Semipermeable Membranes
- Sealing Tape
- Thermoplastic Elastomers
Example of Ionomers:
One example of an ionomer is poly (ethylene-co-methacrylic acid). This polymer is a sodium or zinc salt (which provides the ions) of copolymers derived from ethylene and methacrylic acid.
The common examples of ionomers that serve the commercial requirements include the Polystyrene Sulfonate, Nafion and Hycar:
Important Features of Ionomers
- High stiffness
- High strength
- Good crack resistance, Good
- Good resistance to abrasion
- Good color stability
- Good crack resistance
- Extremely durable
- High Stress Crack Resistance
- Good flexibility
- High flow index
- Excellent impact resistance
- Oil resistant
- Recyclable Material.
Generic Ionomer properties
Specific Gravity : 0.940 to 0.974
Melt Mass-Flow Rate (MFR) @190°C/2.16 kg : 0.65 to 14g/10 min
Tensile Strength @ Yield, 73°F : 1890 to 4100 psi
@Break, 73°F : 1600 to 4910 psi
Durometer Hardness (73°F) : 60 to 65
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