What Is Special about Polymers

Linear polymers are often thermoplastic, meaning they can flow at some temperature depending on the molecular weight. Polymers need not be simple chains but can be branched or networked. Cross-linked polymers can be gels that swell in a solvent or thermosets, which form three-dimensional networks for example, epoxy resins. This interconnectedness allows long-range coupling. 

The physical properties of the reaction medium change dramatically during a reaction. For example, the viscosity almost always increases by orders of magnitude. These changes often will affect the kinetic parameters of the reaction and the transport coefficients of the medium. 

Phase separation is ubiquitous with polymers because the entropy of mixing is low. Miscibility between polymers is the exception unless stronger intermolecular interactions occur, such as hydrogen bonding. 

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