The 20th century has been described as the age of plastic. From the serendipidous discovery of polythene in 1898 by the German Chemist Hans von Pechmann to the equally fortunate accidental discovery of an industrial process for synthesising poly(ethene) in 1933 by the English ICI (Imperial Chemical Industry) scientists Fawcett and Gibson, synthetic polymers have become both ubiquitous and an environmental concern in everyday life.
Syllabus referenceStructure 2.4.4 - Polymers are large molecules, or macromolecules, made from repeating sub-units called monomers.
- Describe the common properties of plastics in terms of their structure.
Guidance
- Examples of natural and synthetic polymers should be discussed.
Tools and links
- Structure 3.2 - What are the structural features of some plastics that make them biodegradable?
What is a polymer?
Polymers are large molecules composed of repeated subunits, known as monomers, which are bonded together to form long chains. These materials are ubiquitous in our everyday lives, manifesting in various forms such as plastics, rubber, and DNA. The versatility of polymers stems from their unique molecular structure, which can be engineered to exhibit a wide range of physical and chemical properties.
Polymers can be classified into two main categories: natural and synthetic. Natural polymers, such as cellulose, silk, and wool, are found in nature and have played a critical role in life's processes for millennia. Synthetic polymers, on the other hand, are human-made and include familiar materials like polyethylene, used in plastic bags, and polystyrene, found in disposable cups.
The physical properties of polymers, such as strength, elasticity, and resistance to chemicals and temperature, are determined by the nature of the monomers used and the way they are linked together. This allows for an incredible diversity of materials, from the tough and durable plastics used in automotive parts to the flexible and lightweight fibers in clothing.
Polymers are not only vital in the manufacturing and textile industries but also play a crucial role in the field of biomedicine. Biodegradable polymers, for example, are being developed for use in drug delivery systems and tissue engineering. The adaptability and wide range of applications of polymers make them an essential and ever-evolving part of modern science and technology.
Natural polymers
Natural polymers are macromolecules found in nature, formed by living organisms. They play a crucial role in various biological processes and are essential components of the natural world. These polymers are made up of monomers that are bonded together to form long chains, and their structure and composition are inherently designed to serve specific functions in nature.
One of the most well-known natural polymers is cellulose, the primary structural component of plants. Cellulose provides rigidity and strength to plant cell walls, enabling plants to grow tall and strong. Another vital natural polymer is DNA (Deoxyribonucleic Acid), which contains the genetic blueprint of living organisms. DNA's unique structure allows it to store and transmit genetic information, playing a fundamental role in heredity and evolution.
Proteins, another class of natural polymers, are composed of amino acids and perform a myriad of functions in living organisms. They act as enzymes to catalyze biochemical reactions, play structural roles in cells and tissues, and regulate bodily functions. For example, collagen, a protein found in connective tissues, gives skin its elasticity and strength.
Natural polymers are not only important for their biological functions but also have various applications in industries. For instance, wool and silk, both protein-based polymers, are widely used in the textile industry. The unique properties of natural polymers, such as biocompatibility and biodegradability, make them increasingly important in sustainable development and biotechnology applications.
Synthetic polymers
Synthetic polymers, unlike their natural counterparts, are human-made materials engineered for specific applications and properties. These polymers are created through a process known as polymerization, where monomers are chemically bonded into long and repeating chains. This innovation has led to the development of a vast array of materials with diverse characteristics and uses.
Synthetic polymers may be broadly sub-divided into addition and condensation polymers, although there are many other subtle forms of modifying the polymeric structures.
Addition polymers
These are formed by addition reactions of unsaturated hydrocarbons. The double bond in an unsaturated molecule opens and attaches to a neighbouring unsaturated molecule. The process continues until a large number of monomer units are joined together in a long chain.
One of the most common synthetic polymers is polyethylene, widely used in the production of plastic bags, bottles, and other packaging materials. Its popularity stems from its durability, flexibility, and resistance to moisture. Another notable synthetic polymer is polystyrene, recognized for its lightweight and insulating properties, making it ideal for use in packaging, disposable food containers, and insulation materials.
Polyvinyl chloride (PVC) is another versatile synthetic polymer used in everything from construction materials to medical devices. Its ability to be both rigid and flexible, coupled with its chemical resistance, makes it suitable for a wide range of applications. Synthetic polymers like nylon and polyester have revolutionized the textile industry, offering alternatives to natural fibers with their strength, durability, and resistance to moisture and wrinkles.
Condensation polymers
These were first developed in the mid-20th Century by joining monomer units together using condensation (addition-elimination) reactions. These polymers are dealt with in depth on the next page
Summary
The development of synthetic polymers has had a profound impact on modern society, offering materials that are integral to various industries, including automotive, aerospace, electronics, and healthcare. However, the environmental impact of these polymers, particularly their non-biodegradable nature, poses significant challenges, driving research towards more sustainable and eco-friendly alternatives.
