Introduction to Materials - Sample Preparation Topic for Transmission Electron Microscopy - page 18

3.3 Polymer Microstructures

Polymers (or macromolecules) are molecular systems composed of a very high
number of atoms (e.g., 1,000 to 100,000 to 1 million or more). Their molecular
masses range between 10,000 and several millions of grams per mole. They are
derived from a process called polymerization. In Fig. 2.5, a distinction is made
between the following:

(a) Linear polymers, soluble polymers.
(b) Branched polymers, whose solubility is close to that of linear polymers but
whose morphology is different.
(c) Crosslinked polymers, which form an insoluble and infusible network (elas-
tomers).
(d) Cyclolinear polymers, which are generally crystalline and have the same
properties as linear polymers, except for solubility.
(e) Ladder polymers, composed of linear molecules in which skeletons are attached
together in regular sequences. They have good thermal properties but low
solubility.

Polyethylene
(PE)

Polyvinyl Chloride)
(PVC)

Methyl Poly-
methacrylate) (PMMA)

Polyacrylonitrile)
(PAN)

Fig. 2.5 Different structures of polymers

Among polymers, a distinction is made between natural polymers (cellulose, nat-
ural rubber from the plant kingdom, silicates from the mineral kingdom, proteins
and nucleic acids from the animal and plant kingdoms), artificial polymers result-
ing from the chemical modification of natural polymers, and synthetic polymers
resulting from human engineering.