Chemistry Reference
In-Depth Information
POLYMER CLASSES
Thermoplastic vs. thermoset
Step growth vs. chain growth
Resins vs. plastics
Homopolymer vs. copolymer
Block vs. graft vs. alternating vs. random
Linear vs. branched vs. crosslinked
End uses
Terms used in classifying polymers can be quite confusing. As we proceed
in our discussion of polymers, we will touch on each of the above terms.
First, polymers can be divided into two classes based on their behavior when
heated.
soften and melt when heated. They make up about
80% of man-made polymers.
Thermoplastics
maintain their original shape when
heated and do not soften or melt. This is due to the crosslinking of polymer
chains to form giant three-dimensional molecules. Polymers may be
Thermosets
step
growth
or
chain growth,
depending on their mechanism of formation. The
terms
refer to polymer products; however, there is much
overlap in the usage of those terms.
resin
and
plastic
is used broadly and covers natural
resins (e.g., shellac, amber, etc.) as well as polymers resulting from reaction
between two or more substances (e.g., phenol-formaldehyde, silicones,
alkyds).
Resin
are high polymers combined with other ingredients such as
plasticizers, accelerants, curatives, etc. and can be formed or molded under
heat and pressure. A
Plastics
homopolymer
is prepared by polymerization of a single
monomer while a
copolymer
is prepared from two or more monomers.
Copolymers may be
whereby monomer A and monomer B are
distributed randomly along the polymer chain;
random,
alternating,
whereby A and
B alternate along the polymer chain;
whereby the polymer chains
consist of sequences of A connected to sequences of B; or
block,
graft,
whereby
chains of B are attached to a backbone chain of A.
