[1] A large number of commercial polymeric products are derived from the blending of two or more polymers to achieve a favorable balance of physical properties.
An example of such pair is the miscible resin NORYL™, a mix of poly(phenylene oxide) and polystyrene.
Since most useful polymers are high in molecular weight, the change in entropy experienced from the mixing of two large polymer chains is very low, and typically does not bring the Gibbs free energy low enough to constitute miscibility.
Most processed polymer mixes consist of a dispersed phase in a more continuous matrix of the other component.
The formation, size, and concentration of this disperse phase are typically optimized for specific mechanical properties.
If the morphology is not stabilized, the dispersed phase may coalesce under heat or stress from the environment or further processing.
[4] This coalescence may result in diminished properties (brittleness and discoloration) due to the induced phase separation.
For example, Nylon-rubber bands are polymerized with functionalized rubber to produce graft or block copolymers.
The added structures make it no longer favorable to coalesce and/or increase the steric hindrance in the interfacial area where phase separation would occur.