50 terms

Material Science Chapter 4

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polymer
many repeating unit. most are hydrocarbons,
the longer the chain, the higher the melting point, the stronger it is⁺
Thermoplastics
Heat moldable or processible, both linear and branched polymers such as most vinyl polymers. They can be repeated used and recycled.
Thermosets
Crosslink under heat, e.g. many resins such as epoxy. They cannot be recycled.
Elastomers
Polymers that can undergo large elastic deformation and recovery, such as rubber.----cannot be recycled.
isomerism
compounds with the same composition may have different atomic arrangements.
monomer
refers to the small molecule from which a polymer is synthesized.
homopolymer
When all of the repeating units along a chain are of the same type.
copolymers
Chains may be composed of two or more different repeat units.
Stereoisomerism
Atoms are linked together in the same order head to tail but differ in their spatial arrangement.
isotactic configuration
All of the R groups are situated on the same side of the chain.
syndiotactic configuration
The R groups alternate sides of the chain.
atactic configuration
For random R positioning.
Cis structure
the CH₃ group and the H atom are positioned on the same side of the double bond. C=C cannot rotate and cannot be interchanged by bond rotation.
Trans structure
the CH3 and H reside on opposite sides of the double bond. C=C cannot rotate and cannot be interchanged by bond rotation.
Linear polymers
are those in which the repeat units are joined together end to end in single chains.
Branched polymer
Polymers may be synthesized in which side-branch chains are connected to the main ones.
Crosslinked polymer
Adjacent linear chains are joined one to another at various positions by covalent bonds. brittle
Network polymer
Multifunctional monomers forming three or more active covalent bonds make three- dimensional networks.
random copolymer
the two different units are randomly dispersed along the chain in.
alternating copolymer
the two repeat units alternate chain positions.
block copolymer
Identical repeat units are clustered in blocks along the chain.
graft copolymer
homopolymer side branches of one type may be grafted to homopolymer main chains that are composed of a different repeat unit.
Natural polymers
Wood, Cotton, Leather, Rubber, Wool and Silk.
R⋅ is an active center
They can be free radical, anions, cations, and coordination centers.
crystallite
A semicrystalline polymer consists of small crystalline regions. plastic
chain-folded model
The molecular chains within each platelet fold back and forth on themselves, with folds occurring at the faces.
spherulite
Many bulk polymers that are crystallized from a melt are semicrystalline
polymer crystallinity
The packing of molecular chains to produce an ordered atomic array.
bifunctional
Monomers that have an active bond that may react to form two covalent bonds with other monomers forming a two-dimensional chainlike molecular structure.
functionality
is the number of bonds that a given monomer can form.
tri-functional Engineering plastics
They have three active bonds, from which a three-dimensional molecular network structure.
Polyethylene (PE)
Carbon and Hydrogen bi-functionally formed
Poly vinyl chloride (PVC)
Carbon, Hydrogen and Chlorine bi-functionally formed.
Polytetrafluoroethylene (PTFE)
Bifunctional polymer with Carbon and Fluorine.
Polypropylene (PP)
Bi-functional polymer with Carbon and Hydrogen but the Carbon splits off in another direction.
aromatic ring
symbol in the backbone chain
Polystyrene (PS)
Conformation of polymers
The spatial arrangements of the polymer chain differing by reasons of rotation about single bonds. Are interchangeable with bond rotations.
Random/ Gaussian Coil of polymers
Countless possibilities of the shape due to rotation around sp3 carbon backbone In the amorphous state. Examples: solutions melted state, and Amorphous solids.
Lamella
~10 nm thick, basic unit of polymer crystal
Single crystals in polymers
crystalize from extremely dilute solution at relatively high temperature and crystallize slowly.
Polymer Crystallinity
Polymers are rarely 100% crystalline.
Tacticity
stereoregularity of chain (spacial arrangement of R units along chain ( all on one side or flipped)
2 types of polymerization
free radical, R∙+C=C →R-C-C∙ +C=C
initiation, propagation, termination
condensation, two monomers combine and leave a water byproduct
degree of polymerization
Dp=Mn/M where Mn=sum(xiMi) is the sum of the fraction of chains in the size range multiplied by the mean weight of the size range
and M is the repeat unit molecular weight
weight average molecular weight
Mw=sum(WiMi) sum of eigth fraction of chains in size range multiplied by the weights of the size range
conformation
mulecular chape of the chain (bending twisting around bonds
configuration
the structure of the molecule, in order to change it, you have to break the bonds and reattach them
glass transition temp
allows chains to rotate
defects
stress and strain
tensil stress sigma=F/A
tensil strain €=delta/L
shear strain y=tan(theta)

elastic deformation is reversible
plastic deformation is permanent
modulus of elasticity sigma=E€
poisson's ratio V=€subL/€