Polymers

Nature of science:

Advances in technology—as a result of advances in technology (X-ray diffraction, scanning tunnelling electron microscopes, etc), scientists have been able to understand what occurs on the molecular level and manipulate matter in new ways. This allows new polymers to be developed. (3.7) Theories can be superseded—Staudinger's proposal of macromolecules made of many repeating units was integral in the development of polymer science. (1.9) Ethics and risk assessment—polymer development and use has grown quicker than an understanding of the risks involved, such as recycling or possible carcinogenic properties. (4.5)

• Thermoplastics soften when heated and harden when cooled.
• A thermosetting polymer is a prepolymer in a soft solid or viscous state that changes irreversibly into a hardened thermoset by curing.
• Elastomers are flexible and can be deformed under force but will return to nearly their original shape once the stress is released.
• High density polyethene (HDPE) has no branching allowing chains to be packed together.
• Low density polyethene (LDPE) has some branching and is more flexible.
• Plasticizers added to a polymer increase the flexibility by weakening the intermolecular forces between the polymer chains.
• Atom economy is a measure of efficiency applied in green chemistry.
• Isotactic addition polymers have substituents on the same side.
• Atactic addition polymers have the substituents randomly placed.

Applications and skills:

• Description of the use of plasticizers in polyvinyl chloride and volatile hydrocarbons in the formation of expanded polystyrene.
• Solving problems and evaluating atom economy in synthesis reactions.
• Description of how the properties of polymers depend on their structural features.
• Description of ways of modifying the properties of polymers, including LDPE and HDPE.
• Deduction of structures of polymers formed from polymerizing 2- methylpropene.

• Plastics were virtually unheard of prior to the second world war. How has the introduction of plastics affected the world economically, socially and environmentally?

Utilization:

• Syllabus and cross-curricular links:
• Topics 10.2 and 20.1—addition and condensation reactions

Aims:

• Aim 6: Physical properties of high and low density polyethene could be investigated or synthesis of a polyester, polyamide or other polymer could be quantitatively performed to measure atom efficiency.

• The equation for percent atom economy is provided in the data booklet in section 1.
• Consider only polystyrene foams as examples of polymer property manipulation.