<P> In the presence of an appropriate photosensitiser, such as methylene blue and light, alkenes can undergo reactions with reactive oxygen species generated by the photosensitiser, such as hydroxyl radicals, singlet oxygen or superoxide ion . These reactive photochemical intermediates are generated in what are known as Type I, Type II, and Type III processes, respectively . These various alternative processes and reactions can be controlled by choice of specific reaction conditions, leading to a wide range of different products . A common example is the (4 + 2) - cycloaddition of singlet oxygen with a diene such as cyclopentadiene to yield an endoperoxide: </P> <P> Another example is the Schenck ene reaction, in which singlet oxygen reacts with an allylic structure to give a transposed allyl peroxide: </P> <P> Polymerization of alkenes is a reaction that yields polymers of high industrial value at great economy, such as the plastics polyethylene and polypropylene . Polymers from alkene monomers are referred to in a general way as polyolefins or in rare instances as polyalkenes . A polymer from alpha - olefins is called a polyalphaolefin (PAO). Polymerization can proceed via either a free - radical or an ionic mechanism, converting the double to a single bond and forming single bonds to join the other monomers . Polymerization of conjugated dienes such as buta - 1, 3 - diene or isoprene (2 - methylbuta - 1, 3 - diene) results in largely 1, 4 - addition with possibly some 1, 2 - addition of the diene monomer to a growing polymer chain . </P> <Dl> <Dd> Structure of bis (cyclooctadiene) nickel (0), a metal--alkene complex </Dd> </Dl>

What type of polymer is made by bonding an alkene to one or more alkanes or alkenes