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Skills for Chemistry: Open Book Paper The reactions involved in the formation of natural and synthetic rubber Natural rubber is formed from the monomer isoprene through addition polymerisation - Figure 1. Monomer isoprene molecules (2-methylbuta-1,3- diene) add on to the growing polymer chain polyisoprene one unit at a time. The double bond in each polymer unit is 98% cis [2] giving rise to rubber's immense tensile strength. It is formed when the two double bonds in isoprene open for polymerisation. High-quality synthetic rubber can be created using three relatively easy methods, unlike natural rubber which requires extremely complex conditions to polymerise [2]: free radical polymerisation of butadiene to form poly(cis- 1,3-butadiene) [4], emulsion polymerisation using butadiene and styrene and polymerising 2-methylpropene. Polybutadiene has similar properties to natural rubber because of its cis arrangement, however in free radical polymerisation the double bonds between the rightmost monomer (see Figure 2) carbons can remain intact to form a short vinyl side group available for branching or cross-linking; this is unlike natural...

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