Polymers

  • Classification of polymers
  • Based on the mechanism of polymerization

Types of polymers

  • Addition polymers
  • Condensation polymers
  • Copolymers
  • Homopolymers
  • Heteropolymers

Addition polymers

  • Formed by the addition of monomer units
  • Ex: Polyethylene, Polypropylene

Condensation polymers

  • Formed by the elimination of small molecules during polymerization
  • Ex: Polyester, Polyamide

Copolymers

  • Formed by the combination of two or more different monomer units
  • Ex: Styrene-butadine copolymer, Ethylene-vinyl acetate copolymer

Homopolymers

  • Consist of only one type of monomer unit
  • Ex: Polypropylene, Polystyrene

Heteropolymers

  • Consist of two or more different types of monomer units
  • Ex: Polyvinyl alcohol, Polyvinyl acetate

Classification based on molecular forces

  • Elastomers
  • Fibers
  • Thermoplastics
  • Thermosetting polymers

Elastomers

  • Exhibit high elasticity and can be stretched
  • Return to their original shape after stretching
  • Ex: Natural rubber, Synthetic rubber

Fibers

  • Have high tensile strength and can be spun into fibers
  • Ex: Nylon, Polyester

Thermoplastics

  • Can be melted and re-molded multiple times without any change in properties
  • Ex: Polyethylene, Polyvinyl chloride (PVC)

Thermosetting polymers

  • Harden upon heating and cannot be re-molded
  • Ex: Bakelite, Epoxy resin

Polymers - Classification of polymers - Based on mechanism of polymerization

  • Step-growth (condensation) polymerization
    • Two monomers react to form a dimer, which then reacts with another monomer to form a trimer, and so on.
    • Example: Nylon-6,6 formation
  • Chain-growth (addition) polymerization
    • Monomers react to form a polymer chain through repetitive addition reactions.
    • Example: Formation of polyethylene
  • Radical polymerization
    • Initiation: Formation of free radicals
    • Propagation: Addition of monomers to growing polymer chain
    • Termination: Combination or disproportionation of radicals to form stable molecules
    • Example: Formation of polystyrene
  • Ionic polymerization
    • Monomers react through ionic intermediates
    • Cations or anions are involved in the reaction mechanism
    • Example: Formation of polyvinyl chloride (PVC)
  • Coordination polymerization
    • Transition metal catalyst coordinates with monomers to form a polymer chain
    • Example: Formation of polypropylene
  • Ring-opening polymerization
    • Polymerization occurs through the opening of cyclic monomers
    • Example: Formation of polyethylene terephthalate (PET)
  • Step-reaction (condensation) polymerization
    • Monomers react in pairs, eliminating a small molecule (usually water) to form the polymer
    • Example: Formation of polyester
  • Addition polymerization
    • Monomers react to form a polymer chain through repetitive addition reactions without any byproducts
    • Example: Formation of polyvinyl chloride (PVC)
  • Copolymerization
    • Two or more different monomers are polymerized together to form a copolymer
    • Example: Styrene-butadiene rubber (SBR)
  • Homopolymerization
    • Only one type of monomer is used in the polymerization reaction
    • Example: Polyethylene

Polymers - Classification of polymers - Based on mechanism of polymerization

Step-growth (condensation) polymerization

  • Two monomers react to form a dimer, which then reacts with another monomer to form a trimer, and so on.
  • Example: Nylon-6,6 formation
    • The reaction between adipic acid and hexamethylene diamine leads to the formation of nylon-6,6.

Chain-growth (addition) polymerization

  • Monomers react to form a polymer chain through repetitive addition reactions.
  • Example: Formation of polyethylene
    • Ethene monomers undergo addition polymerization to form polyethylene.

Radical polymerization

  • Initiation: Formation of free radicals
  • Propagation: Addition of monomers to growing polymer chain
  • Termination: Combination or disproportionation of radicals to form stable molecules
  • Example: Formation of polystyrene
    • Styrene monomers undergo radical polymerization to form polystyrene.

Ionic polymerization

  • Monomers react through ionic intermediates
  • Cations or anions are involved in the reaction mechanism
  • Example: Formation of polyvinyl chloride (PVC)
    • Vinyl chloride monomers undergo ionic polymerization to form PVC.

Coordination polymerization

  • Transition metal catalyst coordinates with monomers to form a polymer chain
  • Example: Formation of polypropylene
    • Propylene monomers undergo coordination polymerization using a Ziegler-Natta catalyst to form polypropylene.

Ring-opening polymerization

  • Polymerization occurs through the opening of cyclic monomers
  • Example: Formation of polyethylene terephthalate (PET)
    • Ethylene glycol and terephthalic acid undergo ring-opening polymerization to form PET.

Step-reaction (condensation) polymerization

  • Monomers react in pairs, eliminating a small molecule (usually water) to form the polymer
  • Example: Formation of polyester
    • Ethylene glycol and terephthalic acid undergo step-reaction polymerization to form polyester.

Addition polymerization

  • Monomers react to form a polymer chain through repetitive addition reactions without any byproducts
  • Example: Formation of polyvinyl chloride (PVC)
    • Vinyl chloride monomers undergo addition polymerization to form PVC.

Copolymerization

  • Two or more different monomers are polymerized together to form a copolymer
  • Example: Styrene-butadiene rubber (SBR)
    • Styrene and butadiene monomers undergo copolymerization to form SBR.

Homopolymerization

  • Only one type of monomer is used in the polymerization reaction
  • Example: Polyethylene
    • Ethene monomers undergo homopolymerization to form polyethylene.