Learn & Review: Introduction to Polymers - Lecture 1.1. - What are polymers?

Understanding Polymers: A Foundational Overview

This summary introduces the fundamental concepts of polymers, defining what they are, how their size is measured, and the building blocks from which they are made. It emphasizes their ubiquitous nature in both natural and man-made forms and their critical importance in life.

What are Polymers?

• Definition: Polymers are macromolecules composed of many repeating units connected end-to-end.
• Etymology: The word "polymer" is derived from Greek:
  • "Poly" means "many."
  • "Mer" means "things," "units," or "numbers."
• Structure: They are characterized as long chain molecules.

Quantifying Polymer Size

Two key parameters are used to describe the size of polymers:

• Molecular Weight:

  • Represents the total molar mass of all atoms in a polymer chain.
  • Units: grams per mole (g/mol) or Daltons.
  • Calculation: Summing the molar masses of all constituent atoms (e.g., carbon and hydrogen in polyethylene).
  • Limitation: While indicating the amount of "stuff" in the molecule, it doesn't directly reveal the chain-like structure or length.

• Degree of Polymerization (n):

  • Represents the number of repeat units in a polymer chain.
  • Often abbreviated as a lowercase 'n'.
  • Indicates the length of the chain in terms of its building blocks.
  • Scale: Very long polymers can have molecular weights in the hundreds of thousands or millions, with degrees of polymerization in the thousands or tens of thousands.

Distinguishing Polymers from Oligomers

• Oligomer: A short fragment of a polymer, typically with a degree of polymerization less than 10.
• Oligomers do not behave like long-chain molecules.

Monomers: The Building Blocks of Polymers

• Definition: Monomers are the small molecule building blocks that are repeated to form a polymer chain.
• Bonding:
  • Monomers are held together by strong covalent bonds along the polymer's backbone.
  • Weaker interactions, such as hydrogen bonding and van der Waals interactions, can also influence the overall structure at a more detailed level.

Examples of Polymers and Their Monomers

• Polyethylene:

  • A simple linear chain polymer.
  • Used in milk jugs and grocery bags.
  • Monomer: Ethylene (though not explicitly named, implied by the structure).

• Biological Polymers:

  • DNA:
    • Formed by covalent bonds between repeat units.
    • Monomers (repeat units): Bases (adenine, cytosine, guanine, thymine).
    • Secondary interactions (hydrogen bonding between strands) are crucial for its double helix structure.
  • Proteins:
    • Formed by covalent bonds between repeat units.
    • Monomers: Amino acids (a library of 20 different types).
    • The arrangement and variety of amino acids lead to precise folding into specific shapes with unique chemical affinities.