Polymer Science
Introduction
Polymer science or macromolecular science is a subfield of materials science concerned with polymers, primarily synthetic polymers such as plastics and elastomers. The field of polymer science includes researchers in multiple disciplines including chemistry, physics, and engineering.
History
The modern understanding of polymers as macromolecules, large molecules with a specific sequence of component units, began with the work of Hermann Staudinger and J.D. Bernal in the 1920s. Staudinger was the first to propose that many common organic compounds that were known to be high in molecular weight were actually made up of large chains of smaller, repeating units linked by covalent bonds.
Structure of Polymers
Polymers are composed of very large molecules made up of repeating subunits, called monomers, connected by covalent bonds. The process of converting monomers into polymers is called polymerization, while the study of polymers and polymerization processes is part of polymer science.
Monomers
Monomers are small molecules, often with a carbon backbone, that can join together to form polymers. An example of a monomer is ethylene, a gaseous hydrocarbon with the formula C2H4. When many ethylene molecules are polymerized, the product is polyethylene, a common plastic material.
Polymer Chains
The backbone of a polymer material is the long chain of carbon atoms. There are also polymers such as silicone, whose backbones consist of alternating silicon and oxygen atoms, with carbon-containing side groups.
Properties of Polymers
Polymers exhibit a wide range of properties, making them suitable for use in a variety of applications. These properties include strength, elasticity, hardness, and glass transition temperature. The properties of a polymer can be modified by copolymerization, the addition of plasticizers, or the addition of fillers.
Strength
The strength of a polymer is determined by the strength of the covalent bonds that make up the backbone of the polymer chain, as well as the intermolecular forces between the polymer chains.
Elasticity
Elasticity in polymers is caused by the chains being able to stretch and then return to their original shape. This is due to the covalent bonds between the atoms in the chain being able to rotate, allowing the chains to become temporarily entangled when strained and then disentangle when the strain is removed.
Hardness
The hardness of a polymer is determined by the degree of cross-linking between the polymer chains. Cross-links are covalent bonds that link one polymer chain to another. When a high degree of cross-linking is present, the polymer material is rigid and brittle.
Glass Transition Temperature
The glass transition temperature (Tg) is the temperature at which a polymer transitions from a hard, glassy material to a soft, rubbery material. Above the Tg, the polymer chains have enough thermal energy to move past each other, which allows the polymer to be molded.
Applications of Polymers
Polymers have a wide range of applications in various fields such as packaging, construction, electronics, aerospace, and medicine.
Packaging
Polymers such as polyethylene, polypropylene, and polyethylene terephthalate (PET) are commonly used in packaging. They are used to make bottles, films, and containers due to their light weight, strength, and resistance to moisture.
Construction
Polymers are used in construction in products such as pipes, doors, windows, tanks, and insulation. Polyvinyl chloride (PVC) is used extensively in construction due to its low cost and durability.
Electronics
Polymers are used in electronics for insulators, adhesives, and as the dielectric material in capacitors. Polymers such as polyimide are used as insulating and packaging materials for integrated circuits and transistors.
Aerospace
In the aerospace industry, polymers are used in the manufacture of lightweight, high-strength materials. These materials are used in the construction of aircraft and spacecraft.
Medicine
Polymers have many uses in medicine, including the manufacture of contact lenses, orthopedic devices, and controlled drug delivery systems. Biodegradable polymers are also used in sutures.
Future of Polymer Science
The future of polymer science lies in the development of new materials with novel properties. These could include polymers with improved strength, elasticity, or chemical resistance, or polymers that are biodegradable or have other environmentally friendly properties.