Polymer Science Overview

Introduction

• Chemists initially doubted the existence of molecules with weights exceeding a few thousand.
• Hermann Staudinger challenged this view, proposing macromolecules (comprised of 10,000+ atoms).
• Staudinger's work, particularly on rubber and cellulose, led to the Nobel Prize in 1953.
• The terms "polymer" and "monomer" originate from Greek roots, signifying "many parts" and "one part," respectively.
• Polymers are crucial for daily life essentials such as food, clothing, and shelter.
• Polymer science and technology have led to diverse materials including plastics, fibers, and resins.
• These materials range in properties from soft silk to strong steel.

Basic Definitions

• Polymer: A large molecule from numerous small repeating molecules joined by covalent bonds.
• Examples: polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), Teflon.
• Molecular weight usually ranges from 10,000 to 100,000.
• Properties differ significantly from individual monomers.

Monomer

• A simple molecule with two or more bonding sites to link with other monomers to grow polymer chains.
• Examples include alkenes, vinyl chloride, adipic acid, and glycol.

Polymerization

• The chemical process transforming small molecules (monomers) into a large polymer molecule.
• Requires each monomer to have at least two bonding sites (e.g., a double bond within a molecule).
• May involve various techniques, like bulk polymerization, to achieve the reaction.
• An initiator (like hydrogen peroxide) may be required to start the process.

Functionality

• The number of bonding sites available in a monomer to participate in polymerization.
• Monomers can be bi-functional, tri-functional, or poly-functional depending on the number of bonding sites.

Commercial Polymers

• Polymethyl methacrylate (PMMA): A transparent thermoplastic.
• Also known as Plexiglass or Lucite, it is easily molded and resistant to organic solvents.
• Applications: windows, lenses, glazing, and many other applications.
• Synthesis involves heating methyl methacrylate monomers in the presence of a catalyst, and bulk polymerization.

Polyurethanes

• Polyurethanes are created via the addition polymerization of a diisocyanate with a glycol (or triol).
• Resultant polymer features the –NHCOO– urethane linkage.
• Usable as elastomers, fibers, coatings, or foams.
• Resistant to corrosive chemicals, oils, and greases.
• Exhibits high stretchability and abrasion resistance.
• Available in both rigid and flexible foam forms.
• Applications include tire treads, industrial wheels, and various fabrications.

Conducting Polymers

• Materials capable of conducting electricity.
• Before 1960, most polymers were considered insulators.
• Polyacetylene (among others) demonstrated electrical conductivity when doped.
• The Nobel Prize in Chemistry was awarded to those who developed these materials in the 1970s.
• Conducting polymers feature a conjugated backbone with alternating single and double carbon-carbon bonds.
• Doping of polymers (with oxidizing or reducing agents) is crucial for electron delocalization and conductivity improvement.
• Advantages: light weight, flexibility, low cost.
• Applications: telecommunication, printed circuit boards, aerospace wiring, and others.

Properties of Polymers

• Polymers exhibit diverse properties influenced by monomer type, structure, and other factors.
• Light weight and chemically stable.
• Easily molded into various shapes and sizes.
• High melting and boiling points due to stronger intermolecular forces.
• Some polymers have strong, elastic properties, especially those with increased chain length and cross-linking.
• Additional properties include tensile strength, transparency, insulation characteristics, corrosion résistance, thermal stability and non-rusting tendencies.
• Applications including their use in lasers, food packaging, and electronic devices.

Biodegradable Polymers

• Biodegradable polymers are an alternative to conventional plastics.
• They can break down into natural substances through the action of microorganisms under specific conditions.
• Can originate from renewable sources like corn starch, wood cellulose as well as be generated by microorganisms from specific chemical substances
• Suitable for applications including replacing existing plastics for packaging, medical implants, and various other applications.

Natural Fibres

• Natural fibres like cotton, hemp, and flax exhibit adaptability, fineness, and a good aspect ratio.
• Suitable as reinforcement in several composites due to properties including superior strength/weight ratio, biodegradability and resistance to low temperatures.
• Processing conditions and moisture absorption properties are important factors.

Surface Modification of Natural Fibres

• Chemical treatments (e.g., alkali, potassium permanganate, and acrylic acid) can alter natural fibres' properties:
  • Strength / flexibility.
  • Improving their adhesion to different polymers.
  • Their interaction with various chemicals.
• These alterations are important for the success of polymer composites fabrication
• Examples: Alkali Treatment for enhanced interactions between polymers and natural materials, and potassium permangnate treatment for increased fibre strength and rigidity.

Polymer Composites

• Combination of two or more materials with different properties.
• Polymer composites often combine polymers with other materials like natural fibers, metals, or other polymers to achieve specific properties (like high strength, low weight).
• Enhanced properties compared to the constituent materials.
• Applications in various industries, from aerospace to automotive to consumer products.