Radiation polymerization - Principles

For the sake of brevity, we'll call "polymerization" any chemical operation that converts a set of n small molecules (mono-mers) into n/N (N>>1) macromolecules.

• In fact, a whole variety of mechanisms are known, among which the following stand out in particular:

  • polymerization in the strict sense of the term (figure 1 1), whether ionic or radical;

  • polycondensation (figure 1 2), whether or not it involves the elimination of small molecules.

Depending on the functionality of the monomers, polymers can be linear (Figures 1 1 and 1 2) or three-dimensional (Figures 1 3, 1 4 and 1 5). The latter can be produced from monomers (figure 1 3) or from polymers that are "point-welded" using reactive functions distributed along the chain (figure 1 4) or at the end of the chain (figure 1 5). These different processes can be combined. Similarly, several types of monomer can be combined. The result is a copolymer.

• In practical terms, a polymerization operation poses a series of problems, including the following.

• Controlling the structure of macromolecules, on which material performance is closely dependent:

  • chain length and, possibly, stereoregularity in the case of linear polymers;

  • network perfection, cross-linking density in the case of three-dimensional polymers.