الخميس، 9 فبراير، 2012

البلمرة


Addition Polymerization

Addition polymers form:

  • when unsaturated carbon (organic) molecules react to form a long chain polymer molecule
  • and no small molecules or atoms are eliminated during the reaction

The general reaction can be represented as: 
nR-C=C-R'  catalyst  
    →    
-(-R
|
C
-R'
|
C
-)n-

where R and R' can represent hydrogen atoms, halogen atoms, alkyl or other carbon-containing side chains.
Monomer Name
Monomer Structure
Polymer Name
Polymer Structure
Polymer Uses
ethene (ethylene)
CH2=CH2
polyethene (polythene or polyethylene)
-[-CH2-CH2-]n-
LDPE for sandwich wrap, cling wrap
HDPE for water pipes, wire insulation

propene (propylene)
CH2=CHCH3
polypropene (polypropylene)
-[-CH2-CHCH3-]n-
electrical appliances, automotive applications, ropes, carpets, films

chloroethane (vinyl chloride)
CH2=CHCl
polyvinyl chloride (PVC)
-[-CH2-CHCl-]n-
indoor electrical conduit, underground water pipes

tetrafluoroethene (tetrafluoroethylene)
CF2=CF2
polytetrafluorethene (polytetrafluoroethylene, teflon)
-[-CF2-CF2-]n-
Insulation for wires, motors, generators, etc.
Anti-stick applications in cookware, bearings.

styrene (vinyl benzene)
CH2=CH
polystyrene
H
|
-[C-
|
H
H
|
C-
|


]n-
heat and electrical insulation, pipes

acrylonitrile (vinyl cyanide)
CH2=CH-CN
polyacrylonitrile
-[-CH2-CHCN-]n-
acrylic fabrics stronger than wool

vinyl acetate
CH3COOCH=CH2
polyvinylacetate (PVA)
-[-CH3COOCH-CH2-]n-
adhesives, paints

Condensation Polymerization

Condensation polymers form:

  • when bifunctional monomers react to form a long chain polymer molecule
  • small molecules, such as water, are eliminated during the reaction
Polyesters, polyamides, proteins and polysaccharides such as cellulose, are all examples of condensation polymers.

Polyesters

Polyesters form when the -OH functional group of one monomer reacts with the -COOH functional group of another monomer. 
An ester link (-COO-) is formed between monomers during the reaction. 
H2O is eliminated in the reaction.
General reaction between a dicarboxylic acid and a diol:
HO
|
C
||
O
- R -OH
|
C
||
O
+HO- R'-OH        OH
|
C
||
O
-R-

C
||
O
-O-R'-OH+H2O

Example: 
terephthalic acid + ethylene glycol          polyethyleneterephthalate (terylene or dacron)

nHOOCCOOH + nHO-(CH2)2-OH      -(-OCCOO-(CH2)2-O-)n- + nH2O


video

Polyamides

Polyamides form when when the -COOH functional group of one monomer reacts with the -NH2functional group of another monomer. 
An amide link or peptide bond (-CO-NH-) forms between monomers during the reaction. 
H2O is eliminated in the reaction.

Proteins are naturally occurring polyamides.
General reaction between a dicarboxylic acid and a diamine:
HOOC-R-COOH + H2N-R'-NH2          HOOC-R-CONH-R'-NH2 + H2O
Example: 
hexanedioc acid + 1,6-hexanediamine          nylon-6,6 + water 
nHOOC-(CH2)4-COOH + nH2N-(CH2)6-NH2    -(-OC-(CH2)4-CONH-(CH2)6-NH-)n- + nH2O

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