CHEM 11/20

Overview of Polymers

  • The presentation discusses two main types of polymers: addition polymers and condensation polymers.

Understanding Addition Polymers

  • Addition polymers are formed by the polymerization of monomers with the same kind of repeating units.

  • Example: Chloroethene polymerizes to form PVC (Polyvinyl Chloride).

  • The atom economy in addition reactions is 100% as there is no loss of atoms.

Introduction to Condensation Polymers

  • Condensation polymers are formed from the reaction of two different monomers, resulting in the loss of a small molecule, typically water.

    • Depicted as:

    • Monomer A + Monomer B 
      ightarrow Condensation Polymer + Water

  • Types of small molecules lost during condensation include: water (H extsubscript{2}O), ammonia (NH extsubscript{3}), or hydrochloric acid (HCl).

  • Condensation reactions involve functional groups:

    • Common functional groups include:

    • Amino group (–NH extsubscript{2})

    • Carboxyl group (–COOH)

Condensation Reactions

  • Definition: A condensation reaction is a chemical reaction where two molecules combine to form a larger molecule while losing a small molecule.

  • Condensation polymers require two functional groups for the reaction to occur.

Types of Condensation Polymers

Polyamides

  • Formed from the reaction between a dicarboxylic acid and a diamine.

  • Example monomers:

    • Dicarboxylic acid: Benzene-1,4-dicarboxylic acid

    • Diamine: 1,4-diaminobenzene

  • Key bond type: Amide link (–CONH–)

  • Biological relevance:

    • Proteins as natural polyamides formed from amino acids via peptide bonds.

    • Peptide bond structure: formed by the dehydration synthesis of two amino acids.

Polyesters

  • Formed from the reaction between a dicarboxylic acid and a diol.

  • Example monomers:

    • Dicarboxylic acid: Phthalic acid

    • Diol: Ethylene glycol.

  • Key bond type: Ester link (–COO–)

Differences Between Addition and Condensation Polymers

  • Addition polymers are created without the loss of any atoms, while condensation polymers involve the elimination of small molecules.

  • This results in different functionalities and applications for each type of polymer.

Properties and Applications of Polymers

  • Polyamide (e.g., Nylon): Used in textiles, reinforcing materials, and automotive applications.

  • Polyester (e.g., PET): Commonly used in fabrics, plastics, and packaging materials.

  • Polysaccharides (e.g., starch, cellulose): Formed from sugar monomers, playing essential roles in biological systems (e.g., energy storage, structural support).

Synthesis of Nylon

  • Demonstration video explains the synthesis of nylon in the lab, showcasing how diamines and dicarboxylic acids react to form polymers.

  • The process involves:

    • Mixing of 1,6-hexanediamine and sebacoyl chloride.

    • Formation of nylon at the interface of two liquids while pulling out strands with a wire or paperclip.

Historical Context and Anecdotes

  • Reference to the rise of polyester clothing in the 1970s, including personal anecdotes about unpleasant experiences associated with polyester garments.

  • Highlighting how condensation polymerization techniques have developed from natural processes observed in biochemistry, particularly through dehydration synthesis in the formation of biological macromolecules.

Conclusion

  • Importance of understanding the relationships between synthetic polymers and natural biological molecules.

  • Encouragement for students to engage with practical demonstrations of polymer synthesis in the lab and its relevance to both natural and synthetic chemistry.

  • Exam Focus: Key concepts for the exam include distinguishing between addition and condensation polymers, identifying their respective monomers and functional groups involved (e.g., amino, carboxyl), recognizing the types of bonds formed (e.g., amide, ester), and knowing specific examples of each polymer type and their applications.