<unk> s can be classified in many ways, but most commonly by their polymer backbone (polyvinyl chloride, polyethylene, polymethyl methacrylate, and other acrylics, silicones, polyurethanes, etc.). Other classifications include thermoplastic, thermoset,<unk> omer, engineering<unk> , addition or condensation or polyaddition (depending on polymerization method used), and glass transition temperature or Tg.
Some<unk> s are partially crystalline and partially amorphous in molecular structure, giving them both a melting point (the temperature at which the attractive intermolecular forces are overcome) and one or more glass transitions (temperatures above which the extent of localized molecular flexibility is substantially increased). So-called semi-crystalline<unk> s include polyethylene, polypropylene, poly (vinyl chloride), polyamides (nylons), polyesters and some polyurethanes. Many<unk> s are completely amorphous, such as polystyrene and its copolymers, poly (methyl methacrylate), and all thermosets.<unk> s are polymers: long chains of atoms bonded to one another. Common thermoplastics range from 20,000 to 500,000 in molecular mass, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as "repeat units", derived from "monomers"; each polymer chain will have several 1000's of repeat units.  The vast majority of<unk> s are composed of polymers of carbon and hydrogen alone or with oxygen, nitrogen, chlorine or sulfur in the backbone.  (Some of commercial interest are silicon based.)  The backbone is that part of the chain on the main "path" linking a large number of repeat units together.  To vary the properties of<unk> s, both the repeat unit with different molecular groups "hanging" or "pendant" from the backbone,  (usually they are "hung" as part of the monomers before linking monomers together to form the polymer chain). This customization by repeat unit's molecular structure has allowed<unk> s to become such an indispensable part of twenty first-century life by fine tuning the properties of the polymer.
People experimented with<unk> s based on natural polymers for centuries. In the nineteenth century a<unk>  material based on chemically modified natural polymers was discovered: Charles Goodyear discovered vulcanization of rubber (1839) and Alexander Parkes, English inventor  (1813—1890) created the earliest form of<unk>  in 1855. He mixed pyroxylin, a partially nitrated form of cellulose (cellulose is the major component of<unk>  cell walls), with alcohol and camphor[citation needed]. This produced a hard but flexible transparent material, which he called "Parkesine." The first<unk>  based on a synthetic polymer was made from phenol and formaldehyde, with the first viable and cheap synthesis methods invented by Leo Hendrik Baekeland in 1909, the product being known as Bakelite. Subsequently poly (vinyl chloride), polystyrene, polyethylene (polyethene), polypropylene (polypropene), polyamides (nylons), polyesters, acrylics, silicones, polyurethanes were amongst the many varieties of<unk> s developed and have great commercial success.
The development of<unk> s has come from the use of natural materials (e.g., chewing gum, shellac) to the use of chemically modified natural materials (e.g., natural rubber, nitrocellulose, collagen) and finally to completely synthetic molecules (e.g., epoxy, polyvinyl chloride, polyethylene).
In 1959, Koppers Company in Pittsburgh, PA had a team that developed the expandable polystyrene (EPS) foam.
On this team was Edward J. Stoves who made the first commercial foam cup.  The experimental cups were made of puffed rice glued together to form a cup to show how it would feel and look.  The chemistry was then developed to make the cups commercial. Today, the cup is used throughout the world in countries desiring fast food, such as the United States, Japan, Australia, and New Zealand.  Freon was never used in the cups, as Stoves said[citation needed]: "We didn't know freon was bad for the ozone, but we knew it was not good for people so the cup never used freon to expand the beads." However, for many years polystyrene foam
The foam cup can be buried, and it is as stable as concrete and brick.  No<unk>  film is required to protect the air and underground water.  If it is properly incinerated at high temperatures, the only chemicals generated are water, carbon dioxide, some volatile compounds and carbon soot.  If properly burned, one ton of foam cups product 0.2 ounces of ash.  Paper cups, when incinerated, produces an average of 200 pounds of ash. Polystyrene burned without enough oxygen or at lower temperatures (as in a campfire or household fireplace) can produce polycyclic aromatic compounds , carbon black and carbon monoxide in addition to styrene monomers. EPS can be recycled to make park benches, flower pots and toys.  Paper cups, which often have more oil in them than a foam cup, cannot be recycled if they are coated.
It is relatively easy to make the cups biodegradable.  One has only to mix rice flour in the polystyrene.  When the micro-organisms eat the rice, they also ingest the polystyrene. But there are three reasons to not make the cups biodegradable: 1. The time frame cannot be set. You don't want the cup disappearing on the grocer's shelf or when you have coffee in it; 2. The products of degradation are not food-grade approved; 3. If people know the material is biodegradable, they throw more cups carelessly away.
Photodegradable is superior but they have to be thrown into sunny places. If you throw the cups under a tree, they will not degrade. Manufacturers of the cups say[citation needed], "If you can teach people to throw the cups into the sunlight, you can teach them to throw them into the trash."
Plastic
Carbromal
Inhalant
Cathartic
Colloid
Phytochemical
Keloid
Geothermal