What Is A Polymer- Polymer Engineering Solutions

A lot of plastic and polymer processing engineers often want to know what is a polymer. In an easy to understand engineer’s language, polymer is described as a material that is capable of flowing through the mold runner and gates to take a defined shape, when heated to a temperature, which is more than its melting point. To describe in the engineer’s language: A molecule has a group of atoms which have strong bonds among themselves but relatively weak bonds to adjacent molecules. Examples of small molecules are water (H2O), methanol (CH3OH), carbon dioxide, and so on. Polymers contain thousands to millions of atoms in a molecule which is large; they are also called macromolecules. Polymers are prepared by joining a large number of small molecules called monomers. Polymers can be thought of as big buildings, and monomers as the bricks that go into them.

Monomers are generally simple organic molecules containing a double bond or a minimum of two active functional groups. The presence of the double bond or active functional groups act as the driving force to add one monomer molecule upon the other repeatedly to make a polymer molecule. This process of transformation of monomer molecules to a polymer molecule is known as polymerization. For example, ethylene, the prototype monomer molecule, is very reactive because it has a double bond.

Under the influence of heat, light, or chemical agents this bond becomes so activated that a chain reaction of self-addition of ethylene molecules is generated, resulting in the production of a high-molecular weight material, almost identical in chemical composition to ethylene, known as polyethylene, the polymer of ethylene (Please refer to the Figure above). The difference in behavior between ordinary organic compounds and polymeric materials is due mainly to the large size and shape of polymer molecules. Common organic materials such as alcohol, ether, chloroform, sugar, and so on, consist of small molecules having molecular weights usually less than 1,000. The molecular weights of polymers, on the other hand, vary from 20,000 to hundreds of thousands.

The name polymer is derived from the Greek poly for many and meros for parts. A polymer molecule consists of a repetition of the unit called a mer. Mers are derived from monomers, which, as we have seen for ethylene, can link up or polymerize under certain conditions to form the polymer molecule. The number of mers, or more precisely the number of repetitions of the mer, in a polymer chain is called the degree of polymerization (DP). Since the minimum length or size of the molecule is not specified, a relatively small molecule composed of only, say, 3 mers might also be called a polymer. However, the term polymer is generally accepted to imply a molecule of large size (macromolecule). Accordingly, the lower molecular- weight products with low DP should preferably be called oligomers (oligoZfew) to distinguish them from polymers. Often the term high polymer is also used to emphasize that the polymer under consideration is of very high molecular weight.
Because of their large molecular size, polymers possess unique chemical and physical properties. These properties begin to appear when the polymer chain is of sufficient length?i.e., when the molecular weight exceeds a threshold value?and becomes more prominent as the size of the molecule increases.

This concludes our discussion about “What is a Polymer” and you should have a fairly good idea about the various properties and constituents a plymer is supposed to possess. If you have any tips or suggestions that you think might be useful for other Plastic Injection Molding Design or Processing related engineers, then do mention them so all can benefit from them. Leave a comment below for such design or processing tips.