Chemistry Reference
In-Depth Information
POLYMER SYNTHESIS
Polymers are prepared by processes in which small molecules undergo
multiple combinations to form very large molecules. There are two principal
types of polymerization:
1. S
. Important polymers manufactured by
step growth are polyamides (nylons), polyesters, and
polyurethanes.
tep growth polymerization
2.
Chain growth polymerization
. Important polymers manufactured
by chain growth are polyethylene, polystyrene, polyacrylonitrile,
and polymethacrylates.
Conditions that are important to all chemical reactions such as stoichiometry
and reactant purity become critical in polymer synthesis. In step growth poly-
merization, a 2% measuring and/or impurity error cuts the degree of poly-
merization or the molecular weight in half. In chain growth polymerization,
the presence of a small amount of impurity that can react with the growing
chain can “kill” the polymerization.
For a polymer molecule, its molecular weight is the number of monomer
units that it consists of multiplied by the molecular weight of the monomer
unit (minus the molecular weight of any by-products of the polymerization).
A molecular weight of at least 5000 is normally required before the polymer
displays useful mechanical properties.
