05 Polymer Materials Free Online FlashCards

What are polymers?

Polymers are materials made from very large molecules, called macromolecules, whose atoms form long chains or networks.

What are monomers in a polymer?

A polymer chain consists of repeating chemical units derived from smaller molecules called monomers.

What are three possible polymer chain architectures?

Polymer chains may be linear, branched, or joined by cross-links.

How do bonds within a chain differ from attractions between chains?

Strong covalent bonds hold atoms together along a chain, while weaker attractions between neighboring chains affect how easily they slide past one another.

How does chain mobility generally affect polymer stiffness?

Greater chain mobility generally makes a polymer softer and more flexible; restricted mobility often increases stiffness.

How do amorphous and semicrystalline polymers differ?

Amorphous polymers have disordered chains; semicrystalline polymers contain both ordered regions and amorphous material.

What does the glass-transition temperature, Tg, indicate?

Tg marks a change in the mobility of amorphous chain segments. Below Tg, an amorphous polymer is typically hard and may be brittle; above it, it becomes more flexible or rubbery.

What happens at a semicrystalline polymer’s Tm?

Tm is the temperature at which the ordered regions of a semicrystalline polymer melt.

What does viscoelastic behavior mean for a polymer under load?

A viscoelastic polymer’s response to a load depends on both how quickly and how long the load is applied.

How does heating allow thermoplastics to be shaped?

Thermoplastics consist mainly of separate, uncross-linked chains. Heating lets them soften and, at suitable temperatures, flow so they can be shaped and cooled to solidify.

What happens to thermosets during curing and later heating?

During curing, thermosets form networks with permanent covalent cross-links. Once cured, they do not melt and flow again when heated; excessive heat eventually degrades them.

What lets elastomers stretch greatly and recover?

Elastomers can undergo large, mostly recoverable deformations. Their flexible chains extend under tension, while a small number of cross-links or physical junctions help them recover when the load is removed.