Karteikarten
Polymer structure
Karten in diesem Stapel (26)
- 1What types of polymers are there?Thermosetting, thermoplastic and elastomers.
- 2What are characteristics of thermoplastics?- Soften and eventually liquifies when heated. Hardens when cooled.
- Above is totally reversible
- Generally soft.
- Mostly linear or branched polymers. - 3What are characteristics of thermosetting polymers?- Highly cross-linked and network polymers.
- Permanently hard, doesn't soften when heated.
- Harder and stronger than thermoplastics. - 4What do many polymers consist of?Many are organic, so hydrocarbons which are hydrogen and carbon atoms.
Most polymers have a carbon back-bone that other atoms can bond with. - 5Atoms in polymers have covalent bonding, what does this mean?In a single covalent bond, the two bonding atoms each share an electron. Double bonded means sharing two pairs of electrons etc.
- 6How many electrons can hydrogen and carbon atoms share (i.e. participate in covalent bonding)?Carbon can share four electrons whilst hydrogen can share one. Refer to periodic table.
- 7How does bond strength influence boiling temperature?A lower bond strength (ex. from hydrogen and Van Der Waals bonds) has a lower boiling point.
- 8What are Mers?In a polymer, you see a pattern that repeats. A single pattern is a Mer unit. Aka. repeat unit.
- 9What is polymerisation?A process to transform mer units into a chain of mer units to form a network.
Ex. ethylene gas to polyethylene. - 10Describe the process of polymerisation.1. An initiator/catalyst reacts with mer unit, breaking a carbon bond and leaves one unbonded electron.
2. Many mer chains follow up due to unbonded electron.
3. Terminator ends the reaction by sharing with unbonded electron. - 11Define molecular weight.Mass of a single chain.
- 12Why do we define an average molecular weight?Can't control length of chain. There is a distribution. Within a material, there are many chains of varying length and hence weight.
- 13What is the difference between number and weight average molecular weight?Number is based on size of chains. Weight is based on mass in each size.
- 14What is degree of polymerisation?Average number of Mers per chain:
(number or weight average molecular weight)/Mass of a Mer - 15What is the importance of ability for chains to rotate?Some mechanical and thermal properties are dictated by their ability to rotate.
- 16What are some common relationships between chains?Linear
Branched
Crosslinked
Networked
- 17What are characteristics of linear polymers?Chains are flexible, extensive Van Der Waals and hydrogen bonding. No direct connection, so no cross-links.
- 18What are characteristics of branched polymers?Side branches connected to main linear branch.
Compared to linear polymers, lower density as packing efficiency is reduced due to branches. Also no direct connection, so no cross-links. - 19What are characteristics of cross-linked polymers?Linear chains are connected. Often covalently bonded.
Can be visualized as branched polymers, but branches are connected with a linear chain at both ends.
Strengthens material. - 20What are characteristics of network polymers?Mers have three or more covalent bonds. Some highly crosslinked polymers fall under this category (ex. epoxy).
- 21Why does highly cross-linked polymers like thermosetting plastics not soften when heated?Extensive covalent bonding. Heat energies electrons which vibrate them, but links resist vibrational and rotation motion.
At super high temperatures, chains may be destroyed. - 22What are copolymers?Polymers consisting of more than one type of Mer.
- 23How is polymer crystallinity defined?Packing of molecular chains to produce an an ordered atomic array.
Imagine putting molecular chains in a box, how neatly the chains fit define crystallinity. - 24How would amorphous and partially crystalline polymers look structurally?Due to crosslinks and branches, amorphous polymers appear random when packed.
Crystalline polymers can be neatly packed due to linearity of chains.
* Both crystalline and amorphous regions appear in polymers. - 25Why are many network and crosslinked polymers amorphous?Crosslinks prevent rearranging and alignment.
- 26What does degree of crystallinity influence?1. Density, higher degree means higher density.
2. Cooling rate when solidifying. More crystalline needs more time.
3. Chain configuration
Informationen
- Beschreibung
- Postgraduate Materials (Topics) Karteikarten am Polymer structure, erstellt von John Wang am 02/06/2024.
- Erstellt von
- John Wang
- Aufrufe
- 0
- Bewertung