Butene, also known as butylene, is an alkene with the formula C4H8. It is a colorless gas present in crude oil as a minor constituent in quantities that are too small for viable extraction. Butene is used as the monomer for polybutene, but this polymer is more expensive than alternatives with shorter carbon chains such as polypropylene. Polybutene is therefore commonly used as a co-polymer (mixed with another polymer, either during or after reaction), such as in hot-melt adhesives.

Linear low-density polyethylene (LLDPE)

Linear low-density polyethylene is a substantially linear polymer (polyethylene) with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins. Linear low-density polyethylene differs structurally from conventional low-density polyethylene (LDPE) because of the absence of long chain branching. The linearity of LLDPE results from the different manufacturing processes of LLDPE and LDPE. LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and such higher alpha-olefins as butene, hexene or octene. The copolymerization process produces a LLDPE polymer that has a narrower molecular weight distribution than conventional LDPE and in combination with the linear structure, significantly different rheological properties.

Low-density polyethylene (LDPE)

Low-density polyethylene is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. Its manufacture employs the same method today. The EPA estimates 5.7% of LDPE (recycling number 4) is recycled. Despite competition from more modern polymers, LDPE continues to be an important plastic grade.


Hexene is an alkene with a molecular formula C6H12. The prefix "hex" is derived from the fact that there are 6 carbon atoms in the molecule, while the "-ene" suffix denotes that there is an alkene present—two carbon atoms are connected via a double bond. There are several isomers of hexene, depending on the position and geometry of the double bond in the chain. One of the most common industrially useful isomers is 1-hexene, an alpha-olefin. Hexene is used as a comonomer in the production of polyethylene.

High-density polyethylene (HDPE)

High-density polyethylene or polyethylene high-density (PEHD) is a polyethylene thermoplastic made from petroleum. It is sometimes called "alkathene" or "polythene" when used for pipes. With a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes, and plastic lumber. HDPE is commonly recycled, and has the number "2" as its resin identification code (formerly known as recycling symbol).

Medium-density polyethylene (MDPE)

Medium-density polyethylene is a type of polyethylene defined by a density range of 0.926–0.940 g/cm3. It is less dense than HDPE, which is more common. MDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. MDPE has good shock and drop resistance properties. It also is less notch sensitive than HDPE. Stress cracking resistance is better than that of HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags and screw closures.


A metallocene is a compound typically consisting of two cyclopentadienyl anions (Cp, which is C5H−5) bound to a metal center (M) in the oxidation state II, with the resulting general formula (C5H5)2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride, vanadocene dichloride. Certain metallocenes and their derivatives exhibit catalytic properties, although metallocenes are rarely used industrially. Cationic group 4 metallocene derivatives related to [Cp2ZrCH3]+ catalyze olefin polymerization. Metallocenes are a subset of a broader class of organometallic compounds called sandwich compounds.


Octene is an alkene with the formula C8H16. Several isomers of octene are known, depending on the position and the geometry of the double bond in the carbon chain. The simplest isomer is 1-octene, an alpha-olefin used primarily as a co-monomer in production of polyethylene via the solution polymerization process. Several useful structural isomers of the octenes are obtained by dimerization of isobutene and 1-butene. These branched alkenes are used to alkylate phenols to give precursors to detergents.


Polymers are substances whose molecules have high molar masses and are composed of a large number of repeating units. There are both naturally occurring and synthetic polymers. Among naturally occurring polymers are proteins, starches, cellulose and latex. Synthetic polymers are produced commercially on a very large scale and have a wide range of properties and uses. The materials commonly called plastics are all synthetic polymers. Polymers are formed by chemical reactions in which a large number of molecules called monomers are joined sequentially, forming a chain. In many polymers, only one monomer is used. In others, two or three different monomers may be combined. Polymers are classified by the characteristics of the reactions by which they are formed. Polyesters are an important class of commercial polymers, as are polyamides (nylon).

Rotational Molding

Rotational Molding (also known as rotomolding — or in British English, rotomoulding) involves a heated hollow mold which is filled with a charge (powder) or shot weight (pellet) of material. It is then slowly rotated (usually around two perpendicular axes) causing the softened material to disperse and stick to the walls of the mold. In order to maintain even thickness throughout the part, the mold continues to rotate at all times during the heating phase and to avoid sagging or deformation also during the cooling phase. The process was applied to plastics in the 1940s but in the early years was used sparingly because it was a slow process restricted to a small number of plastics. Over the past two decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage.