Fundamentals of Polymerisation and Organic Addition Reactions

Organic Addition Reactions of Alkenes

The chemical behavior of alkenes is defined significantly by addition reactions, where unsaturated molecules react with other substances to form saturated products. One such reaction presented involves the conversion of propene into propane through the addition of hydrogen. The chemical equation for this process is written as $CH_3-CH=CH_2 + H_2 \rightarrow CH_3-CH_2-CH_3$. In this transformation, the hydrogen atoms add across the double bond of the propene molecule, resulting in the formation of a saturated alkane chain.

Another key example of an addition reaction is the synthesis of chloroethan from ethene and hydrogen chloride. The reaction is represented by the formula $CH_2=CH_2 + HCl \rightarrow CH_3-CH_2Cl$. In this instance, the hydrogen and chlorine atoms from the hydrogen chloride molecule attach to the carbon atoms previously joined by a double bond, effectively saturating the molecule. The product obtained from this specific hydrohalogenation is identified in the transcript as chloroethan.

The addition of hydrogen bromide to a four-carbon alkene, specifically but-2-ene, produces a brominated alkane. The reaction is documented as $CH_3-CH=CH-CH_3 + HBr \rightarrow CH_3-CH_2-CHBr-CH_3$, which the transcript labels as the formation of 2 - bromo butane. Despite the textual transcription recording the product formula as CH-CH-CHB9- CH 2, it chemically represents the addition of $HBr$ across the internal double bond of the butane skeleton to yield 2 - bromo butane.

Introduction to Polymerisation

Polymerisation is essentially the chemical process by which simple molecules join together to create large, complex molecules. Within this context, the simple molecules that serve as the building blocks are called monomers. The resulting large and complex structures formed through this process are known as polymers. The etymological roots of the word polymer provide insight into its structure: "poly" means many, and "mer" refers to a unit or part. Consequently, a polymer is a large molecule made of many repeating units.

Based on the specific chemical method used to facilitate the joining of these molecules, polymers are broadly classified into two distinct types: addition polymers and condensation polymers. This classification helps chemists and engineers understand the structural properties and the mechanical reactions required to synthesize various synthetic materials used in daily life and industrial applications.

Classification and Mechanism of Addition Polymers

Addition polymers are characterized by their method of formation, which involves the repeated addition reaction of monomer units. Unlike condensation polymerisation, this process generally involves the sequential attachment of unsaturated monomers without the loss of smaller molecular fragments. Prominent examples of such materials include polythene and polyvinyl chloride, which are ubiquitous in modern manufacturing.

One specialized addition polymer is Polytetrafluoroethene, more commonly known by the trade name Teflon. This substance is synthesized from the monomer tetrafluoroethene. The chemical equation for the polymerisation of this compound is expressed as $nCF_2=CF_2 \rightarrow \text{Polytetrafluoroethene}$. In this reaction, $n$ represents a large number of individual tetrafluoroethene molecules that link together to form the long-chain polymer. Teflon is widely recognized for its industrial and domestic utility, particularly as a coating for cookware due to its heat resistance and non-stick properties.

Overview of Specific Monomers and Resultant Polymers

Table 2.1 in the transcript provides a list of specific monomers and the polymerisation products associated with them. The monomer vinyl chloride is linked to the production of polyvinyl chloride, often shortened to PVC. Similarly, the monomer ethene is the basis for the creation of polythene. These polymers form the backbone of the plastics industry and illustrate the versatility of addition reactions in generating diverse material types from simple alkene precursors.

Additional monomers mentioned in the source material include isoprene, tetrafluoroethene, and acrylonitrile. Isoprene is the fundamental monomeric unit for polyisoprene, which is the chemical basis for natural rubber. Tetrafluoroethene, as established, is the precursor for Polytetrafluoroethene (Teflon). Finally, acrylonitrile is listed as a primary monomer used in the formation of specialty polymers. The study of these monomers confirms the wide-ranging applications of polymerisation in producing everything from household non-stick pans to industrial rubber products.