Polymer Class

Severalcommon objects that are made of polymeric materials: plastic tableware (spoon, fork, and knife), billiard balls, a bicycle helmet, two dice, a lawnmower wheel (plastic hub and rubber tire), and a plastic milk carton. (Photography by S. Tanner.)

Now, we are talking about the third class of material, polymer. Before we discuss about this class, we have to know what polymer is.

Definition :

The word polymer literally means "many parts." So that’s why it call poly-because it consist of many part of monomer.
Another definition is:

Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule.[1]-

A molecule that consists of repeated, linked units, with each unit being called a monomer.

[2]-

A material that contains many chemically bonded parts or units which themselves are bonded together to form a solid. [3]-

Properties:

Polymers have properties that distinguish with other materials.

Polymer are:

• less dense than metals or ceramics,
• resist atmospheric and other forms of corrosion,
• offer good compatibility with human tissue,
• exhibit excellent resistance to the conduction of electrical current,
• extremely ductile and pliable (i.e., plastic), which means they are easily formed
  into complex shapes,
• have low electrical conductivities

Structure:
A single polymer molecule may consist of hundreds to a million monomers and may have a linear, branched, or network structure.

Atomic Bond:
Covalent bonds hold the atoms in the polymer molecules together and secondary bonds then hold groups of polymer chains together to form the polymeric material. Copolymers are polymers composed of two or more different types of monomers.

Fotenote:
1. http://www.answers.com/topic/polymer
2.http://wiki.answers.com/Q/What_is_a_polymer&src=ansTT
3.http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Introduction/polymers.htm

Reference:
1.http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Structure/polymer.htm