Humans started making objects around 100000 years ago with the materials such as metals, wood, and rock. The evolution in material sciences has resulted in new ways of arranging atoms to produce materials that have revolutionized our daily lives. Polymer, a long-chained giant molecule made of repetitive branching of a single monomer unit, is one such material that we encounter daily in our modern-day lives. Polymers are mainly categorized into two forms based on their origin. Natural polymers are those which we get from animals or plants, e.g., wool, cotton, silk, etc., whereas synthetic polymers are synthesized or artificially created by humans in labs. Although there is a wide variety of synthetic polymers with distinct properties caused by the variations in the main chain and side chains, they are classified into four main categories based on their functionality: thermoplastics, thermosets, elastomers, and synthetic fibers. The backbones of most synthetic polymers are made up of carbon-carbon bonds, while side chains made up of elements like oxygen, sulfur, or nitrogen can be introduced alongside the backbone to create heteropolymers. Synthetic polymers that do not contain any carbon-carbon bond are known as inorganic synthetic polymers, e.g., polysiloxane (silicone–oxygen backbone). Synthetic polymers are crucial in many aspects of modern-day lives. From packaging and wrapping to textiles and building materials, synthesized polymers are integral parts of today’s industry. Let’s take a look at some of the synthetic polymers and their uses in our everyday lives.
Low-Density Polyethylene (LDPE)
Low-Density Polyethylene (LDPE) polymers are one of the most popular types of synthetic organic polymers found in everyday life. It is a thermoplastic polymer manufactured from the monomer ethylene. LDPE was one of the first polymers to be synthesized, and Imperial Chemical Industries synthesized it in 1933 using a high-pressure free radical polymerization technique. The most prominent feature of LDPE is its side branching that prevents the polymers from getting near enough to each other to experience the highest dispersion forces. As a result, the attraction is very faint and results in the polymer density range of 917–930 kilograms per cubic meter. The plastic formed from low-density polyethylene has a low melting point, is easily molded and its low density makes it buoyant in water. The most common use of LDPE is in the manufacturing of plastic bags that we use to carry items; however, certain governments around the globe have banned the use of plastic bags due to rising environmental concerns. LDPE is also used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic parts for computer components, and various molded laboratory equipment.
High-Density Polyethylene (HDPE)
High-density polyethylene (HDPE), sometimes called “alkathene” or “polythene,” is also a thermoplastic polymer produced from the monomer ethylene. In comparison to LDPE, it is a cost-effective thermoplastic with a linear structure and no or low degree of branching. It takes 1.75 kilograms of petroleum (in terms of energy and raw materials) to make one kilogram of HDPE. The density of HDPE can range from 930 to 970 kilograms per cubic meter. Although HDPE is only marginally more in density than LDPE, it is the intermolecular forces and less branching that give HDPE its tensile strength. It is manufactured at low temperature (70-300°C) and low pressure (10-80 bar). While its higher density versions yield a more rigid result, HDPE can vary in flexibility. Because HDPE shows low reactivity to its environment, it is used to produce containers that are suitable for storing a wide range of compounds.HDPE pipes benefit from the same qualities that make them remarkably effective in containers. HDPE pipes are chemically resistant, allowing them to convey a wide range of liquids and serve as an outer cover for cables and wires. HDPE can resist temperatures ranging from -220°F to 180°F when adequately strengthened for this use. Sewer, water, gas pipes, and coatings over automotive wires, are some of the few applications of HDPE pipes. The cost-effective nature of HDPE makes it a preferable replacement in several areas where plastic is required, e.g., in 3D printers, banners, hovercrafts, and even in plastic surgery.
Polypropylene (PP)
Polypropylene ({C}_{3}{H}_{6})_{n} is one of the most versatile and cost-effective thermoplastic polymers in all plastics. It is a rigid and partially-crystalline polymer produced via chain-growth polymerization of propene (or propylene) monomer. It has several properties that make it a better choice of plastic than polyethylene, e.g., higher melting point makes it employable in the manufacture of microwave-safe containers, and higher resistance to cracking and stress, even when flexed, makes it less vulnerable to daily wear and tear. It’s one of the most affordable plastics on the market today, and it’s used in industries including automotive manufacture, furniture assembly, and aerospace as both a plastic and fiber. It is used in a variety of applications such as packaging and labeling, textiles, stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. It’s a tough polymer created from the monomer propylene that’s resistant to a wide range of chemical solvents, bases, and acids.
Polyvinyl chloride (PVC)
After polyethylene and polypropylene, polyvinyl chloride (PVC) is the third most extensively used material. It is a high-strength thermoplastic material that comes in two basic forms, rigid and flexible. It is produced by the polymerization of vinyl chloride monomer. It’s a white, brittle solid that comes in powder or granule form. PVC is now replacing conventional building materials such as wood, metal, concrete, rubber, ceramics, and others in a variety of applications due to its versatile properties such as lightweight, durability, low cost, and ease of processing. PVC is utilized in construction because it is less expensive and more durable than traditional materials like copper or ductile iron. Plasticizers, the most common of which are phthalates, can be used to make them softer and more flexible. PVC is utilized in clothes and upholstery, electrical wire insulation, inflatable items, and a variety of other applications where the rubber is replaced.
Polystyrene (PS)
Polystyrene (PS) is an aromatic polymer manufactured from the liquid petrochemical styrene as its monomer. Polyester can be both an amorphous and a semi-crystalline polymer, depending on its manufacturing and thermal history. To generate a fabric with aggregate qualities, polyester fibers are frequently combined with natural fibers. Polyester synthetic fibers outperform plant-derived fibers in terms of water, wind, and environmental resistance. Its hydrophobic nature makes it perfect for clothes and jackets that will be used in damp conditions. Adding a water-resistant treatment to the fabric enhances this impact. PS is a colorless solid that is used in disposable flatware, plastic models, CD and DVD cases, and smoke detector housings, among other applications. Packing materials, insulation, and foam drink cups are all created from foamed polystyrene. Its sluggish biodegradation is a source of debate, and it is frequently seen scattered outdoors, especially near shorelines and rivers.
Nylon
The term ‘nylon’ is most commonly associated with a superstrong silky fiber that is commonly found in umbrellas, socks, and ropes. Nylon is a generic term for a group of polyamides in chemistry (polymers with repeating monomer units linked by amide bonds). Nylons are made by reacting difunctional monomers having equal amounts of amine and a carboxylic acid, resulting in amides at both ends of each monomer. Wallace Carothers at DuPont’s research laboratory first synthesized nylon, a family of synthetic polymers known generically as polyamides, on February 28, 1935. One of the most widely utilized polymers is nylon. Nylon is more hydrophilic than the polymers described above because of its amide backbone. Observe how your nylon clothing absorbs water; this is because nylon, unlike the exclusive hydrocarbon polymers that make up most plastics, can form hydrogen bonds with water.
Teflon (Polytetrafluoroethylene)
Teflon (Polytetrafluoroethylene or PTFE) is a tetrafluoroethylene fluoropolymer that has a wide range of applications. PTFE (polytetrafluoroethylene) is a solid, high-molecular-weight polymer made completely of carbon and fluorine. Water and water-containing compounds cannot interact with PTFE because it is hydrophobic. It is one of the slipperiest man-made substances. Because of its extensive properties, such as exceptional heat and chemical resistance, good electrical insulating power in hot and wet environments, low dielectric constant, strong anti-adhesion, and flexibility, PTFE is used as a cost-effective solution for industries ranging from oil and gas, chemical processing, industrial, to electrical/electronic and construction sectors. Because of its low friction with other compounds, PTFE is utilized as a non-stick coating for pans and other kitchenware. It is often used in containers and piping for reactive and corrosive chemicals because of its low reactivity, which is due in part to the strength of carbon-fluorine interactions.
Thermoplastic polyurethanes (TPU)
Thermoplastic polyurethane (TPU) is any of a class of polyurethane plastic. It has several excellent attributes, including flexibility, transparency, and resistance to oil, grease, and abrasion. The fact that TPU is hydrophilic and can react with water accounts for the majority of these qualities. Technically, TPU is a block copolymer generated by the reaction of (1) diisocyanates with short-chain diols (so-called chain extenders) and (2) diisocyanates with long-chain diols, which results in alternating sequences of hard and soft segments or domains. An enormous range of distinct TPUs can be created by altering the ratio, structure, and/or molecular weight of the reaction chemicals. This allows urethane scientists to fine-tune the structure of the polymer to the material’s desired final qualities. Automotive instrument panels, caster wheels, power tools, sporting goods, medical devices, drive belts, footwear, inflatable rafts, and a range of extruded film, sheets are just a few of the applications of TPU. It is also a common material used in the manufacturing of exterior cases of mobile electrical gadgets like phones, and it is also used to build laptop keyboard protectors. TPU is well-known for its use in wire and cable jacketing, hose, tube, adhesive, textile coating applications, and as a polymer impact modifier.
Polysiloxane
Polysiloxane, also known as silicone, is a class of inorganic polymer compounds consisting of a silicon-oxygen backbone with organic groups, typically methyl groups, attached to the silicon atoms. Silicones can be made with a wide range of characteristics and compositions by altering the lengths, side groups, and crosslinking of the SiO chain. These characteristics include high-temperature resistance, durability, superior electrical insulation, and changing transparency. Silicone rubber is widely used in industries such as aerospace, automotive, construction, medical, energy, food processing, and others because of its unique properties. Silicone sealants and adhesives, in particular, are utilized in the aviation and construction industries to seal and protect doors, windows, wings, and electrical components. Silicones are frequently employed in the medical industry for implants and drug delivery systems due to their non-toxic qualities. Today’s exterior paints and varnishes can withstand the sun and pollutants thanks to advances in silicone technology. Silicone-based paints have excellent adhesion, pigment dispersion, chemical, weather, and stain resistance.
Polyphosphazene
Polyphosphazenes include a wide range of hybrid inorganic-organic polymers with several different skeletal architectures possessing a ‘backbone’ of alternating nitrogen and phosphorous atoms. They are by far the largest class of synthetic inorganic polymers. The high thermal-oxidative stability of the polymer backbone has been explained by the high oxidation state of the nitrogen and phosphorous atoms; however, the substituents are the main influence on the polymer’s physical properties. The characteristics properties of polyphosphazene are bio-compatibility, flexibility, high dipole moment, a broad range of {T}_{g} (glass transition temperature), chemical inertness, mechanical strength, elastomeric nature, and flame-retardancy. These properties can be varied over a wide range by changing the type of side groups, molecular weight, and cross-link density. The variety in properties that polyphosphazenes have resulted in an increased demand for the material in the engineering sector. For instance, elastomeric (fluorinated) polyphosphazene can be employed as heat resistant seals in O-rings, gaskets, and foamed products as fire and heat resistant sound-insulation materials. Because of its biocompatibility, potential for complex customization, a strong affinity for water, and ability to receive grafts of influencing substituents, polyphosphazene is considered ideal medical polymers. Moreover, polyphosphazene is currently the highest performing membrane material for Methanol-based Proton-Exchange Membrane (PEM) Fuel Cells. This fuel cell type is ideal for miniature power supply and is a leading candidate for automotive applications.
Nitrile Rubber (Polybutadiene)
Nitrile rubber, commonly known as Buna rubber, Buna-N, and NBR, is a synthetic rubber copolymer of acrylonitrile (ACN) and butadiene. An important factor in the properties of NBR is the ratio of acrylonitrile groups to butadiene groups in the polymer backbone, referred to as the ACN content. The lower the ACN content, the lower the glass transition temperature; however, the higher the ACN content, the better resistance the polymer will have to nonpolar solvents. Applications that require both solvent resistance and low-temperature flexibility have an ACN content of 33% in the polymer. The great temperature stability of NBR, which ranges from 40 to 108 ° C. (40 to 226 ° F), makes it a perfect material for aeronautical and nuclear applications. The uses of nitrile rubber also include disposable non-latex gloves, automotive transmission belts, hoses, oil seals, V belts, static & dynamic hydraulic seals, synthetic leather, printer’s form rollers, and as cable jacketing; NBR latex can also be used in the preparation of adhesives and as a pigment binder.