10.2 d & e- Outline the addition polymerization of alkenes (ethylene)

10.2d Outline of the addition polymerization of alkenes.

10.2e Describe the relationship between the structure of the monomer to the polymer and repeating unit.

Polymers- Long-chain molecules synthesized by bonding subunit groups (monomers) together

Monomers- individual repeating subunits in a polymer

Proteins are polymers of amino acids -- (polypeptides)	Polyvinyl chloride (PVC)
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a. Properties

  1. Can be very large compounds - 10⁴ - 10⁶ g/mol 

  2. Can have a large diversity of molecular architecture; (linear, branched, ladder & star) 

  3. Have variable solubilities, depending upon solvent and molecular structure

  4. Can be melted and formed into different shapes- Plastics *

b. Synthesis

 * chain-growth polymerization - the mechanism for producing polymers from unsaturated hydrocarbons

  - substrates can be alkenes, substituted alkenes, alkynes, allenes, isocyanates and some cyclic hydrocarbons) 

  - reaction proceeds via radical chain mechanism when heated under high pressure (1000 atm) and a small amount of organic peroxide (diacyl peroxide)

 Steps:

  1. Initation- the mechanism requires an initiator unit which readily forms a radical. Commonly are peroxides, disulfides, or azo groups. Two examples are benzoyl peroxide and AIBN.

  2. Chain propagation- chain builds by forming terminal radicals

  3. Chain transfer (chain branching)- a growing chain can undergo "back-biting" by removing a hydrogen from an axial position which causes an axial radical formation

      or a chain can attack the center of another chain. Both of these lead to branching

  4. Chain termination - termination occurs when two radicals combine (combination) or by forming two different products; alkene + alkane (disporportionation)

Resource: Mechanism description (animation of mechanism)

* Condensation polymerization commonly occurs when polymers are produced through the loss of small molecules, commonly water (methanol can also occur)

 - This requires substrates that have two functional groups per monomer, dicarboxylic acids, dihydroxyls (glycols) or diamines.

 - Common in the formation of polyesters, polyamines, polyacetals and polypeptides (other are polycarbonates, polyurethanes and epoxy resins)

 - sometimes referred to as step-growth polymerization 

Example:

 Mechanism:

Video: Formation of a peptide bond (Khan Academy)