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Last week of class: The lecturer mentions that it is the last Friday and next week will be the last week of class.

Polymer properties: The lecturer discusses the properties of polymers, including different monomers, strand length, interactions between strands, density, crystallinity, and cross-linking.

Thermoplastics: The lecturer explains that thermoplastics are solid polymers with long strands bonded together by IMFs, such as van der Waals and H bonds. They can be reheated and reprocessed, making them recyclable.

Thermosets: The lecturer mentions that thermosets are polymers that have been cross-linked, resulting in a high density of cross-links. They are harder and cannot be reheated or reprocessed.

Differences between thermoplastics and thermosets: The lecturer highlights the differences between thermoplastics and thermosets, including their ability to be reheated and reprocessed, and the presence of cross-links in thermosets.

Thermosets are difficult to recycle because their cross-links are strong and can cause the material to catch fire when heated

Elastomers have light cross-linking, which gives them some elasticity and allows for viscoelasticity

Elastomers fall in between thermosets and plastics in terms of cross-linking, allowing for some uncurling of the polymers before reaching a point where cross-linking restricts movement

Elastomers must be above their glass transition temperature (Tg) to be free to move

Polymers can crystallize, but due to their amorphous nature, they often form a glass instead

The polymer has both crystalline and amorphous regions

The amorphous region is a solid below the glass transition temperature

Heating the polymer causes the crystalline region to melt, while the amorphous region remains a solid

Above the melting point, the entire polymer becomes a liquid

The behavior of the polymer at different temperatures affects its properties, such as elasticity

Elastomers are an important part of the polymer property ecosystem

Composition and sequence control polymer properties

Homopolymers have one type of mer, while copolymers have two

Polymer properties can be controlled by alternating, random, or grafted sequences

Block copolymers allow for engineering specific properties by controlling the blocks or grafts

Surlyn is a polymer that provides clarity, toughness, and versatility

Surlyn is a graft polymer with one type going along the chain and the other type made to form ionic bonds

Surlyn is an ethylene copolymer with an ionic bond, also known as an ionomer

Surlyn's ionic bonding allows for strength, thermal responsiveness, and flexibility

Diapers are an example of a copolymer made out of acrylic acid that can absorb water due to the presence of sodium ions

Steel is strong but not very flexible

Nylon is not as strong as steel but has a lot of elongation

Fiberglass is a plastic reinforced glass that has more flexibility than steel but still only 3-4% elongation

Nitrile rubber is a copolymer that can be tuned for strength and elongation by adjusting the composition

Nature is a polymer engineer gone wild, with a wide range of polymers and properties

Nature has more possibilities in polymerization due to the ability to have different functional groups everywhere

Nature can have many different combinations of amino acids, resulting in a vast number of possibilities

Nature's choice for the R group in amino acids allows for almost limitless flexibility in polymer engineering

Nature has had 1 billion years to experiment with combinations, resulting in the world we know today

Nature's flexibility in polymer engineering is impossible for humans to fully understand

Nature makes polymers through condensation polymerization

Amino acids form peptide bonds through condensation polymerization

Proteins are made from 20 different amino acids, giving them tunability in properties

Spider silk is an example of nature's incredible polymer synthesis

Spider silk is five times stronger than steel and maintains strength below 40 degrees C

Spider webs have an elastic property of 4x and can be stretched to four times their original strength

Nitrile rubber also has high elastic elongation

Spider webs are fully recycled by spiders, who eat their old webs and make new ones the next day

Tires are difficult to recycle due to their high vulcanization and cross-link density

Promising directions in polymer research include self-healing polymers, fully recovering polymers back to monomers, and making easily breakable but heavily cross-linked thermosets