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8/14/2019 Ch13 Polymers
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MS211
Ch. 13 Polymers
Spring 2009
Seokwoo Jeon
Department of Materials Science and Engineering
KAIST
Movie
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Polymers = many mers
= plastic (due to plastic deformation)
Chemical category
Metal and ceramics : inorganic material
Polymerization: the process by which long-chain or
network molecules are made from relatively small organic
molecules. Types of Polymerization
Chain rowth additional ol merization
Step growth (condensation polymerization)
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Chain reaction of chemically activated monomers (i.e. from
additional polymerization by adding monomers
Ex 1. V in l ch loride ol vin l chloride
Polymerization is the joining of individual. ., , 2 3
form a polymer [(C2H3Cl)n] consisting of
manymers (again, C2H3Cl).
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Ex 2 . ethylenepolyethylene H2O2 2OH-
Until ethylene monomers are fully
Detailed mechanism of polymerization by a chain growthprocess (addition polymerization). In this case, a molecule ofy rogen perox e, 2 2, prov es wo y roxy ra ca s,
which serve to initiate and terminate. The polymerization ofethylene (C2H4) to polyethylene -(C2H4)-n. (The large dotnotation re resents an un aired electron. The oinin orpairing of two such electrons produces a covalent bond,represented by a solid line(-).]
terminator
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A polymer derived from two or more monomers
Alternating copolymers
Periodic copolymerse. . A-B-A-B-B-A-A-A-A-B-B-BRandom copolymersBlock copolymersGraft co ol mers
vinyl chloride is analogous to asolid-solution metal alloy.
Ablend of polyethylene andpolyvinyl chloride is analogous toa metal alloy with limited solidsolution
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Prof. S. Kims work at KAIST
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Polymerization by reactive functional group (slower compared to chain growth)Formation of phenol-formaldehydeTwo phenol molecules are linked by the formaldehyde moleculeBifunctional linear molecular structurePolyfunctional network molecular structure
Polyfunctional monomer
3-D network molecular structure
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Degree of polymerization length of the polymeric molecule, size of molecule, howmany mers, Viscosity, light scatteringy g gIn case of 1D linear polymerRoot-mean-square length mlL =Extended length
2
5.109sinmlL
o
ext=
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Higher degree of polymerization rigidity and melting point increasesNetwork molecular structure rigid, brittleLinear molecular structure soft (due to Van der Waals bet. Chains)Symmetry of chain
As the side groups become
Isotacticarger an more rregu ar,
Rigidity and melting pointincreases.
SyndiotacticWhy?
- Hindrance to molecularSyndiotacticsliding
- secondary bonding force
Atactic
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Branching Cross-linking
Branching involves adding a polymeric
structure. Vulcanization.
molecule to the side of the mainmolecular chain.
Accidently found by Charles Goodyear.
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Thermoplastic Polymers
Soft and deformable upon heatingLinear or branched polymeric moleculesGeneral-use polymerL d it l th l (LDPE)ow-density polyethylene (LDPE)Engineering polymerhigh-density polyethylene (HDPE) ultra-high molecular-weight polyethylene(UHMWPE) acrylonitrile butadiene styrene (ABS)UHMWPE), acrylonitrile-butadiene-styrene (ABS)Thermoplastic elastomersRigid elastomeric domains in a relatively soft matrix
Thermosetting Polymers
Hard and rigid upon heatingNetwork molecular structure formed by the step-growth mechanismEnhanced by high temperature and irreversibleHigh strength and stiffness, not being recylableTraditional elastomersAdhesives
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1. Plasticizer
to soften polymer, low molecular weight
.to strengthen polymer, volume replacement to reduce cost.
short-fiber cellulose, asbestos, carbon black (tire rubber)
3. Stabilizerto reduce polymer degradation by oxidation, thermal, or ultraviolet
.
5. Colorantsgmen : nso u e ~ 2, 2 3- 2
Dyes : soluble ~ organic colorants