Common Terms used in Polymers

Defined polymers melt when heated and solidify when cooled. Such materials can be melted several times but each heating step breaks some polymer chains and thus gradually degrades the material.

There are three translations of the term "thermoset" (i.e., Termofijos, Termofijados y Termoestables in Spanish) which is defined as cross linked polymers that once solid do not soften when heated again. Thermostable polymers should not be confused with polymers stable at high temperatures, because the former are always intertwined while the latter may be thermoplastic or thermoset.

These three types of polymers are thermosets but have different properties.

 

Resins have a high degree of cross linking and a Tg higher than the temperature of use. Therefore, they are rigid and barely expand in any solvent.

 

Elastomers, gums or rubbers have a lower degree of cross linking than resins and a Tg below the temperature of use. Consequently, they are flexible and expand considerably in some solvents.

 

Hydrogels have a degree of cross linking in the same order of magnitude as that of elastomers although a bit higher, but what most defines them is that they are hydrophilic and expand in water to masses of ten to 1000 times their dry weight.

Mechanisms and techniques are different things. The various polymerization mechanisms differ by the active species in the polymerization reaction (e.g., radical, anionic, cationic, stepped, etc.) while polymerization techniques are distinguished by the medium in which the reaction takes place (e.g., in a solution, block or mass, suspension, emulsion, etc.).

 

Addition polymerization, condensation polymerization, step-growth polymerization, and chain polymerization (PCR) are different mechanisms. PCR is also called addition polymerization. This term should not be confused with polyaddition, which is a special type of polycondensation reaction in which low molecular weight compounds are not released in each step of the reaction.

The different conformations of a macromolecule are the spatial distributions that can accommodate its atoms. The greater the degree of polymerization, the greater the number of possible conformations there will be for a chain. However, sometimes there is only one or a limited number of them possible (e.g., helix, stick, ball, etc.) as greater stability of the formation of hydrogen bonds and hydrophobic interactions is reached. The conformations interconvert into each other by rotation around the bonds that form the skeleton.

 

The various configurations of a macromolecule are its stereoisomers, i.e., there are different spatial distributions of atoms that can be interconnected only by breaking bonds and not by rotation.