polymers Flashcards
describe a polymer
synthetic material made up of repetition of high weight moleciules in the form of a flexible chain
describe the composition of a polymer and the process used to synthesize them.
the polymer is made up of monomers, which are smaller molecules bonded covalently (strong). Polymers are made through polymerization, which links the monomers together
describe and compare the two types of polymerization
the addition polymerization is the simplest one, where the monomers don’t lose or gain any atoms to bond to each other. The polymers that result from this process tend to be easily recyclable. Condensation polymerization requires the exclusion of an atom in the two monomers, leaving a byproduct. The polymers issued by this process aren’t easily recyclable, as the chemistry is more involved to get the monomers back to their original states.
what are the differences between the polymers designed in long chains and polymers that are cross-linked?
long chained polymers are weaker and more flexible, as the bonds that hold them together are Van der Waals bonds. Cross-linked polymers are more rigid and brittle, but also more strong. This is due to the fact that the long chains are covalently bonded with one another.
name the three main types of polymers.
thermoplastics, thermosets and elastomers
describe the properties of thermoplastics.
Usually recycleable (addition polimerization), reshapeable when heat is applied, anisotropic, indefinite shelf life, ductile
describe the properties of thermosets.
thermosets have a cross-linked structure and are a product of condensation polymerization. They are therefore more brittle and strong. Once they are set they cannot be reshaped. They are isotropic and have a limited shelf life
Describe the properties of elastomers
mostly linear structure with some cross linking (between thermosets and thermoplastics). They require little force to deform due to their low elastic modulus. They can stretch a lot and return to their original form, they are flexible, tough, impermeable and resistant to corrosion
what is the flat portion on the stress/strain curve for elastomers?
It is due to the crystallinity arising out of stretching the chains
what are silicones
silicones are not based on carbon, therefore they are inorganic polymers (Si backbone). They are low in toxicity, have thermal and chemical stability.
what is functionnality and how does it affect the polymer?
its a measure of the amount of sites where the monomers can attach to each other. bifunctionnal for two site and trifunctionnal for three sites. Trifunctionnal polymers may form stronger 3d networks.
What happens when a polymer molecule gets bigger
its melting point increases, its strength increases and its stiffness increases
what polymers have lower thermal conductivity?
foamed plastics
What kinds of polymers are good for transmitting measurable amounts of fluids
solid polymers, due to their low permeability.
describe photo-oxydation
the chains react with atmospheric oxygen, resulting in cross linkage. This leads to embrittlement of the material, which may not be the desired properties of the material.
Name and describe additives for polymers.
plasticizers: lowers glass transisition temperature in amorphous polymers (polymers that ressemble glass).
Fillers: gives more volume to the polymers but doesn’t improve properties, used to reduce cost.
reinforcement agents: improves mechanical properties
stabilizers: improve heat resistance, UV and oxydation (stabilizes, duh)
describe glass transition temperature.
It is the temperature where amorphous polymers transition from glassy, brittle materials to acting more like elastomers
what is a crystalline polymer?
polymers with a linear and regular matrix such as metallic or ionic crystals. They gain that nomenclature when neighboring chains align. They have amorphous zones and crystal-like zones. The latter is called micelle. Higher crystalinity provides higher strength.
foamed polymers and foamed in-place insulation. Describe them now!
foamed polymers: low desitity polymers, they can be rigid or more plastic
foamed in-place insulation: liquid resin that is put in between two elements (walls or ceilings). It then expands and gets air-cured. It must be protected from abrasion , flame and ultraviolet light.
