- Describe how the chemical structure of a polymer relates to its physical properties.
- Synthetic polymers are human-made polymers. They can be classified into four main categories: thermoplastics, thermosets, elastomers, and synthetic fibers. They are commonly found in a variety of consumer products.
- Various main chains and side chains are used to make different synthetic organic polymers. The backbones of common synthetic polymers are made of carbon-carbon bonds, whereas heterochain polymers have other elements (e.g. oxygen, sulfur, nitrogen) inserted along the backbone.
- The seven most common types of synthetic organic polymers are: low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon, Teflon, and thermoplastic polyurethane (TPU).
- thermoplastic: a polymer that becomes pliable or moldable above a specific temperature and returns to a solid state upon cooling
- synthetic polymers: human-made polymers
Synthetic polymers are human-made polymers. From the utility point of view, they can be classified into four main categories: thermoplastics, thermosets, elastomers, and synthetic fibers. Thermoplastics are a type of polymer that become moldable and malleable past a certain temperature, and they solidify upon cooling. Similarly, thermosets similarly become hard and cannot change shape once they have set; for this reason, they are often used in adhesives. An elastomer—a term used interchangeably with rubber—is a flexible polymer. Synthetic fibers are created by improving upon natural plant and animal fibers and make up a large category of polymers.
Poly acrylates are the backbones of common synthetic polymers such as polythene and polystyrene. They are made up of carbon-carbon bonds, whereas hetero chain polymers such as polyamides, polyesters, polyurethanes, polysulfides, and polycarbonates have other elements (e.g. oxygen, sulfur, nitrogen) inserted along the backbone. Coordination polymers may contain a range of metals in the backbone, with non-covalent bonding present. A wide variety of synthetic polymers are also available with variations in their main chains and side chains.
Synthetic Polymers in Everyday Use
Some familiar household synthetic polymers include nylons in textiles and fabrics, Teflon in non-stick pans, and polyvinyl chloride in pipes. The common PET bottles are made of a synthetic polymer, polyethylene terephthalate. The plastic kits and covers are mostly made of synthetic polymers like polythene, and tires are manufactured from Buna rubbers. Due to the environmental issues created by these synthetic polymers, which are often non-biodegradable and synthesized from petroleum, alternatives like bioplastics are also being considered; these bioplastics are often more expensive than synthetic polymers, however.
Many polymers are made entirely from hydrocarbons. This makes them hydrophobic, meaning they do not readily absorb water; this is a useful trait, as the alternative—imagine a water bottle that becomes soggy when filled with water, for instance—might be disastrous.
Types of Synthetic Polymers
Low Density Polyethylene
Low Density Polyethylene (LDPE) polymers are among the most common types of synthetic organic polymers, which are often found in households. LDPE is a thermoplastic made from the monomer ethylene. One of the first polymers to be created, it was produced in 1933 by Imperial Chemical Industries using a high pressure process via free radical polymerization. It is manufactured the way method today. LDPE is commonly recycled, with the number 4 as its recycling symbol. Despite competition from more modern polymers, LDPE continues to be an important plastic grade.
High Density Polyethylene
High Density Polyethylene (HDPE) or polyethylene high-density (PEHD) is a polyethylene thermoplastic made from petroleum. It takes 1.75 kilograms of petroleum (in terms of energy and raw materials) to make one kilogram of HDPE. HDPE is commonly recycled, with the number 2 as its recycling symbol.
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications, including packaging and labeling, textiles, stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An additional polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases, and acids.
Polyvinyl Chloride (PVC) is the third-most widely produced plastic, after polyethylene and polypropylene. PVC is used in construction because it is cheaper and stronger than more traditional alternatives such as copper or ductile iron. It can be made softer and more flexible by adding plasticizers, the most popular of which are phthalates. In this form, PVC is used in clothing and upholstery, electrical cable insulation, inflatable products, and many applications in which it replaces rubber.
Polystyrene (PS) is an aromatic polymer made from the monomer styrene, a liquid petrochemical. One of the most popular plastics, PS is a colorless solid that is used, for example, in disposable cutlery, plastic models, CD and DVD cases, and smoke detector housings. Products made from foamed polystyrene include packing materials, insulation, and foam drink cups. Its very slow biodegradation is a focus of controversy, and it can often be found littered outdoors, particularly along shores and waterways.
Nylon, a family of synthetic polymers known generically as polyamides, was first produced on February 28, 1935 by Wallace Carothers at DuPont’s research facility. Nylon is one of the most commonly-used polymers. The amide backbone present in nylon causes it to be more hydrophilic than the polymers discussed above. Notice that your nylon clothing will absorb water, for instance; this is because nylon can engage in hydrogen bonding with water, unlike the purely hydrocarbon polymers that make up most plastics.
Teflon (Polytetrafluoroethylene or PTFE) is a synthetic fluoropolymer of tetrafluoroethylene, and has numerous applications. PTFE is a solid, high-molecular-weight compound consisting entirely of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances can interact with PTFE. PTFE is used as a non-stick coating for pans and other cookware because it has very low friction with other compounds. It is very non-reactive, partly because of the strength of carbon–fluorine bonds, so it is often used in containers and pipework for reactive and corrosive chemicals. Where used as a lubricant, PTFE reduces friction, wear, and energy consumption of machinery. Although the widespread belief that Teflon is the result of NASA space projects is not true, it has been used by NASA .
Thermoplastic polyurethane (TPU) is any of a class of polyurethane plastic. It has many useful properties, including elasticity, transparency, and resistance to oil, grease, and abrasion. Most of these properties are resultant of the fact that TPU is hydrophilic and can react with water. Technically, TPU is a thermoplastic elastomer consisting of linear segmented block copolymers made of hard and soft segments.