Main Chemical Routes for Synthesis of Polymer Networks

1 Swelling Index Swelling is defined as the increase in volume of a gel or solid associated with the uptake of a liquid or gas [7]. In fact, swelling represents the first stage in every polymer solution process, in which the solvent molecules diffuse through the polymer matrix to form a swollen, solvated mass, known as polymer gel. However, the gel formed after swelling polymer networks does not break up and the polymer molecules do not diffuse out of the swollen mass, and therefore, no real solution can be formed. 

3 MAIN CHEMICAL ROUTES FOR SYNTHESIS OF POLYMER NETWORKS 

From a general point of view, chemical crosslinking processes can be classified into four major types of reactions step-growth polymerization, free radical polymerization, vulcanization, and end-linking of prepolymers. 

Many thermoset polymers of major commercial importance are synthesized by step-growth polymerization, as the case of unsaturated polyester, polyurethanes, melamines, phenolic and urea formaldehyde resins, epoxy resins, silicons, etc. In these systems, the crosslinking process, which leads to a polymer network formation, is usually referred to as curing. 

FRC of a vinyl monomer with a small amount of divinyl monomer represents one of the simplest methods for synthesizing polymer networks. In these systems, the divinyl monomer acts both as a comonomer and as a crosslinker. One of the most common and studied systems of this type is the copolymerization of styrene (STY) and divinylbenzene (DVB). Poly(STY-cri-DVB) copolymers are widely used as ion-exchange resins and separation media for size-exclusion chromatography, although several other vinyl/divinyl copolymerization systems have also been smdied [18], 

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