General aspects in polymer synthesis.

Abstract

The term, synthetic polymer, denotes a macromolecule composed of simple structural units and usually derived from monomers by a process of polymerization. This process is possible only if certain chemical, thermodynamical, and mechanistic conditions are satisfied. The monomer must have a functionality of two or higher. The polymerization process must be characterized by a negative free energy change. The monomer must have activable or reactive functions. Activable structures are polarizable multiple bonds, and bonds entailing heteroatoms in ring compounds. Suitable reactive functions are those that participate in: carbonyl addition, substitution, multiple bond addition, and free-radical coupling. According to their growth mechanisms, polymerization reactions are divided into two major groups: chain-growth polymerization and step-growth polymerization. Polyaddition and polycondensation occur in either group, but polyinsertion is a chain-growth process exclusively. Radical, ionic, and heterogeneous initiations are entailed in chain growth, whereas both nucleophilic and electrophilic initiation prevails in step-growth. The chemical structure of polymers is determined mainly by constitutional and configuration parameters. Principal constitutional ones are related to interlinking of chains and structural units, composition, substituents, endgroups, and the molecular weight. Configurational ones refer particularly to the position of substituents on a central chain atom relative to the neighboring structural unit and thus to the tacticity of the polymer.