Lesson 4

Polymers can be classified based on their applications.
The categories include commodity polymers, engineering polymers, and specialty polymers.

Engineering polymers have exceptional mechanical and thermal properties.
They are used in high-temperature and chemical-resistance applications.
Examples include aerospace composites, flame-retardant textiles for race car drivers, and surgical implants.

Specialty polymers have unique characteristics, such as flame retardancy, ultra-high strength, and conductivity.
Increasing cost and decreasing volume of production from commodity to specialty polymers.

Polyamides can have either aliphatic or aromatic chain backbones.
They are semi-crystalline thermoplastics.
Examples include:
- Nylon-6 (Poly(ϵ-caprolactam))
- Nylon-6,6 (Poly(hexamethylene adipamide))
- NomexTM (Meta-aramid)
- KevlarTM (Para-aramid)

Nylon-6 (Poly(ϵ-caprolactam)) is formed by ring-opening polymerization.
Nylon-6,6 (Poly(hexamethylene adipamide)) is formed by condensation polymerization.
Melting temperature of Nylon-6 is $220$ °C.
Melting temperature of Nylon-6,6 is $265$ °C.
Applications include strings for musical instruments, surgical sutures, and airbags.

NomexTM (Meta-aramid) is formed by condensation polymerization.
KevlarTM (Para-aramid) is formed by condensation polymerization.
Melting temperature of NomexTM is $350$ °C.
Melting temperature of KevlarTM is $500$ °C.
Applications include cut-resistant gloves, fire suits, honeycomb cores used in aircraft, bulletproof vests, and military helmets.
Kevlar has high flame test performance compared to High Performance Polyethylene (HPPE).

ABS is made up of three monomers: acrylonitrile, butadiene, and styrene.
ABS is an amorphous polymer.
Styrene monomer gives ABS good processability and a smooth surface finish.
Acrylonitrile monomer provides stiffness, heat, and chemical resistance.
Butadiene monomer makes the product more tough and impact-resistant, even at low temperatures.
ABS is popular in consumer goods like toys, laptop casings, home appliances, and automotive parts.

Also known as acrylic glass.
PMMA is an amorphous polymer.
Refractive index of $1.49$ , hence offers high light transmittance, allowing 92% of light to pass through, higher than glass.
High resistance to UV light and weathering.
Good chemical resistance.
Its monomer is methyl methacrylate, polymerized via addition polymerization.
Applications include car windows, aquariums, and handphone screen protectors.

PC is an amorphous polymer with attractive engineering properties, including high impact strength, low moisture absorption, low combustibility, good dimensional stability, and high light transmittance (refractive index of $1.58$ ).
PC is synthesized by the condensation of bisphenol-A and phosgene.
Applications include roofing, lenses, windows, and suitcases.

After World War I, advances in polymer technology resulted in new forms of plastics, with the most significant to the optical industry being the invention of polymerized methyl methacrylate (PMMA) in the 1930s.
In 1983, lenses made of polycarbonate were introduced.
Polycarbonate use has grown in popularity due to its high impact resistance.
Children and high-risk individuals are often fitted with this lens when the risk of eye injury outweighs the optical disadvantages.

Comprise a class of engineering thermoplastics with high thermal, oxidative, and hydrolytic stability and good resistance to aqueous mineral acids, alkali, salt solutions, oils, and grease.
High biocompatibility and ability to be sterilized by a variety of techniques make them highly suitable for medical applications.
High permeability makes them attractive as membrane polymers.
Applications include dialyzers, milk bottles, passenger service units in aircraft, and ultrafiltration membranes for water treatment and food processing.
The excellent properties of polysulfones contribute to the repeating units of sulfonyl groups.
Examples include Polysulfone (PSU), Polyethersulfone, and Polyphenylsulfone.

Fluoropolymers have an extremely low coefficient of friction, high-temperature stability, low dielectric constant, and dissipation factor.
Fluoropolymers can be characterized by the strong carbon-fluorine (C-F) bonds.
Fluoropolymers are chemically inert, having greater resistance to acids, bases, and solvents.
Applications include non-stick pans, coatings on irons, and air/gas sampling bags (Teflon).

Specialty polymers are characterized by their ability to retain desirable mechanical, thermal, and chemical properties when subjected to harsh environments.
These polymers can also be tailored to deliver specific properties in various fields of industry.
Polymers covered in this module:
- High-temperature thermoplastics
- Conductive polymers
- Superabsorbent polymers
- Specialty polyolefins

Examples include Victrex® (Polyetheretherketone - PEEK), Kapton® (Polyimide - PI), and Ultem® (Polyetherimide - PEI).
PEEK components have high wear resistance and can retain excellent thermal and chemical resistance properties at high temperatures. Glass Transition Temperature (Tg) $145$ °C
Kapton exists in the form of film, offering excellent chemical resistance and dimensional stability. The properties allow it to be used at both high and low-temperature applications. Glass Transition Temperature (Tg) $385$ °C
Ultem® offers outstanding thermal resistance with low smoke evolution. It also has excellent chemical and lipid resistance. Glass Transition Temperature (Tg) $217$ °C

In general, polymers are good insulators as they do not conduct electricity.
However, the unique polyacetylene makes it a great electrically conductive polymer.
Applications include flexible electronic devices, artificial muscles, and biosensors.

SAP serves a broad range of applications due to their strong affinity for water, absorbing up to 500 times their own weight of liquid.
SAP is synthesized from acrylic acid monomers and sodium hydroxide in the presence of a cross-linking agent.
Applications include diapers, water retention agents, and wound dressings.
In agriculture, SAP polymer particles act like a semi-permeable membrane, absorbing water via the osmosis process.

Specialty polyolefins are small volume, high-performance thermoplastics with high-profit margins compared to traditional commodity polyolefins.
Poly(4-methyl-1-pentene) (PMP) and ultrahigh molecular weight polyethylene (UHMWPE) are some of the most common specialty polyolefins in the market.
PMP applications include medical packaging, films, semiconductors, and gas separation membranes.
UHMWPE applications include hip, knee, and spine implants; suspension lines on sport parachutes; and engine components.