Polymer is a macro-molecule made up by reacting many smaller molecules known as monomers. The properties of a polymer is a function of primary and secondary bonding. Most importantly, polymer science is a multidisciplinary subject, generally studied by chemists, chemical engineers and material engineers.
History Of Polymer Science
Humans have been using polymers long ago, in the form of natural polymers. The polymers in use were: silk, cotton, wood, wool, leather etc. In 1885, first polymer was synthesized, a semi-synthetic polymer known as nitrocellulose. Nitrocellulose was made flexible with the help of a plasticizer, called camphor. It was used to film movies. Later on, it was also used as varnish for furniture etc.
The property that hindered its widespread use was its flammability due to the nitrate group. Afterwards, nitrate was replaced by acetate. Later on artificial silk was also synthesized which led to the production of rayon.
The first purely synthetic polymer was synthesized in 1910, Bakelite, a densely crosslinked polymer formed by the reaction of phenol with formaldehyde. At that time, polymers were synthesized by hit and trial method and little was known about the relation between its chemical structure and its physical properties.
In 1920, Staudinger came up with the macromolecular hypothesis. This was the time when polymer science caught the attention of scientists. Carothers, a DuPoint Chemist, suggested that if the macromolecular hypothesis is true, then if a diacid is reacted with diols, with the reaction stoichiometry of one to one, then these molecules should react forming a long chain. Carothers discovered polyester, succeedingly synthesizing nylon and neoprene.
Primary bonding is chemical bonding between atoms, which is a result of complete electron transfer, or mutual transfer of electrons. There are three main types of primary bonding :
Secondary bonding is physical bonding between atoms or molecules. This plays a role in the physical properties of a polymer and other materials. Examples of secondary bonding are Van Der Waal forces, dipole-dipole interactions, hydrogen bonding, etc.
When many molecules of the same type are joined, properties of large collection of molecules are measured, known as bulk properties. Bulk properties are a function of:
- Molecular Properties
- Collective Properties
These properties depend upon the molecular nature of materials such as chemical reactivity.Moreover, the reactivity further defines the type of polymer formed and the ease with which a polymer can be formed.
These properties depend upon the interaction of molecules with each other in a material, for example crystal formation is a collective property. Furthermore, these properties will dictate the level of crystalline nature of a polymer.
Degree of polymerization
Degree of polymerization tells how many monomeric units have chemically reacted to form a certain polymer. Degree of polymerization is given by the formula :
Degree Of Polymerization =
(Molecular Weight of Polymer)/(Molecular weight of monomer)