Many different classifications are significant.
Step polymerization produces polymers with a wide range of molar masses, the average molar mass rising steadily with longer reaction times. Thermosoftening plastics can be made by either mechanism whereas thermosetting plastics are necessarily step polymers. The most important step polymers are the condensation polymers , such as polyesters and polyamides . The polymers have much larger molar masses than the monomers, typically by factors ranging from thousands to hundreds of thousands. The New Penguin Dictionary of Science 2.