32 Questions
Which type of bonds hold monomers together into a chain or macromolecule?
Covalent bonds
What is the primary characteristic of thermoset polymers?
Crosslinking of the polymer occurs
Which type of forces are created when atoms and molecules in polymers approach each other but do not result in electron sharing or transfer?
Secondary bonds
What is the process by which a polymer is formed known as?
Polymerization
Which classification of polymers can be melted and reformed into various shapes multiple times?
Thermoplastics
What type of bonds are rare in polymers but can be found in some cases?
Ionic bonds
What mainly determines the ability of a polymer to crystallize?
The regular placement of atoms in the chain
Which material is an example of a semicrystalline polymer?
Polyethylene (PE)
What causes some important sources of polymer irregularity in terms of crystallinity?
Stereochemical irregularity
Which type of linear polymer can easily crystallize?
Linear polymers made of symmetrical unsaturated monomers
Which factor does polymer morphology mainly depend on?
Chemical composition and chain configuration
In terms of crystallinity, what is atactic PP considered to be?
Amorphous
What is the Ultimate Elongation of a material?
The maximum strain a material can bear before rupturing
Which property is largely a result of the amorphous regions in a polymer?
Resilience
How is the toughness of a polymer typically measured?
By the area under the stress-strain curve
What does brittleness in materials refer to?
Inability to experience significant strain without rupture
Which characteristic decreases with increasing crystallinity and orientation in polymers?
Resilience
What does creep in materials refer to?
The tendency of the material to deform over time under constant load
What does impact strength measure in polymers?
Ability to resist fracture when exposed to sudden impact
Which type of impact test is often used for plastic film samples?
Dart drop impact test
How is impact strength determined in the dart drop impact test for plastic film?
By recording the weight of the dart that ruptures the film
What aspect of polymers do thermal properties describe?
Relationship with temperature
What does the melting temperature (Tm) refer to in polymers?
Temperature at which a polymer transitions from solid to liquid state
Which property is closely related to impact strength according to the text?
Toughness
What is the important determinant of the overall properties of a polymer?
Molecular architecture + chemical composition + molecular weight
Which type of polymer structure generally yields a more compact arrangement of atoms?
Linear structure
What does functionality refer to in the context of polymerization?
The number of bonds a monomer can form during polymerization
Which type of polymer is formed when the functionality of a monomer is 2?
Linear polymer
Which type of polymers are formed from monomers with the structure CH2=CHX or CH2=CXY?
Addition polymers
How are addition polymers mainly produced?
By free radical polymerization
Which type of molecule fragment contains an unpaired electron and is involved in free radical polymerization?
Free radical
What happens during addition polymerization?
Monomers are added into the polymer chain directly
Study Notes
Tensile Properties
- Elastic Limit: the maximum stress a material can experience without undergoing permanent deformation
- Ultimate Elongation: the maximum strain a material can bear before it ruptures/breaks
- Resilience: the ability of a material to absorb energy and then return to its original dimensions
- Resilience is a property largely of the amorphous regions in the polymer
- Resilience decreases with increasing crystallinity and orientation in the polymer
- Toughness: the energy a material can absorb before rupturing
- The toughness of a polymer can be measured by the area under the stress-strain curve
- Impact tests also measure toughness, where polymers are tested at high strain rates
- Brittleness: the inability of a material to experience a significant amount of strain without rupture
- Brittleness is often associated with a lack of toughness
- Creep: the tendency of a material to deform over time when subjected to a constant load
- Creep is a result of the viscoelastic nature of plastics, where molecules tend to slowly change their positions when subjected to extended stress, leading to significant deformation over time
Types of Polymers
- Examples of polymers: PE, PP, PVC, PTFE, PAN, PA, PMMA, PET
- Examples of copolymers: ABS, E/P, VC/VA, VC/VD, VC/E
Bonds in Polymers
- Primary bonds: hold monomers together into a chain or macromolecule
- Covalent bonds: formed by the sharing of a pair of electrons, common in polymers
- Ionic bonds: formed by the complete transfer of an electron from one atom to another, rare in polymers
- Secondary bonds: examples include hydrogen bonds and van der Waal's forces, which are intermolecular forces between chains or neighboring molecules
Classification of Polymers
- Thermoplastics: can be melted and formed into various shapes repeatedly, examples include PE, PP, PVC, and PS
- Thermosets: crosslinking of the polymer occurs, shape and dimensions are set permanently after the initial heating, examples include unsaturated polyester resin and epoxy resin
- Commodity plastics: high volumes, modest price, reasonable performance, examples include polyethylene, polypropylene, polystyrene, and poly(vinyl chloride)
- Engineering plastics: maintain mechanical properties above 100°C, higher price, and superior thermo-mechanical properties, examples include nylon, polyester, and polycarbonate
Polymerization
- Polymerization: the process by which a polymer is formed, involving a catalyst/initiator, solvent (optional), monomers, and secondary chemicals (optional)
- Polymerization reactor: a schematic representation of the polymerization reaction process, which is maintained under controlled temperature and pressure
Crystallinity of Polymers
- Crystallinity: the ability of a polymer to crystallize, determined by the regular placement of atoms in the chain
- Sources of polymer irregularity: stereochemical irregularity, copolymers with random placement of comonomers, and branching in polymeric structure
- Polymer morphology: the fine structure of plastic, including amorphous and crystalline regions, which can coexist in a polymer sample
- Examples of polymers: LDPE, HDPE, PET, and EVOH, which are semicrystalline, and general-purpose polystyrene, which is amorphous
Mechanical Properties of Polymers
- Impact strength: the ability of a polymer to resist fracture when exposed to sudden impact, closely related to toughness
- Impact strength is measured using different types of impact tests, including the dart drop impact test for plastic film
Thermal Properties of Polymers
- Thermal properties: the relationship between polymer properties and temperature
- Melting temperature (Tm): the temperature at which a polymeric material transitions from a solid to a liquid state
Test your knowledge on different types of polymers such as PVC, PTFE, and Nylon, along with examples of copolymers like ABS and E/P. Learn about primary bonds in polymers including covalent bonds that hold monomers together in a macromolecule.
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