Systems with functionality greater than 2. Freezing point
Polycondensation, polyaddition and polymer modification

The systems studied in this section involve AA + BB + RA_f or AB + AB + RA_f + RB_{f '}, in which f and f ′ are greater than two, and lead to the formation of networks characterized by branches and bridges between chains.

The formation of these networks is characterized by the appearance of two phases in the reaction medium:

• the gel phase, consisting of an infinite network swollen by the solvent ;

• the sol phase, which contains the soluble polymer.

Frost increases at the expense of the soil. Frost occurs at a critical value p_c of p, which corresponds to the frost point and is referred to as the critical degree of advancement. Several theories account for these phenomena, often involving highly complex mathematical treatments; the two simplest are given below.