Physico- Chemical Structure of Polymer,

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Polymers are difficult to classify because there are so many interacting relationship among the large number of polymeric materials now in existence.

Four most methods of classifications are

1.       Physico chemical structure

2.       Mode reparation

3.       Physical properties

4.       Technical applications

 

A.      Physico Chemical structure

                Functionality: - The ultimate result of coupling monomers to produce polymers is wholly dependent on the functionality of monomer. Molecule is called Mono-, bi-,tri-, or polyfunctional depending on the number of reactive bonds or groups available for coupling at beginning or during course of polymeric reaction.

1.       Unifunctional  (U-), Example: CH3.COOH where carboxyl (COOH) group is the oly chemically reactive group.

2.       Bifunctional (-B-) ex. CH2=CH2, where the double bond splits to form coupling with another molecule containing double bond, Not necessarily ethylene . 

                                Polyethylene  = –(CH2-CH2)-

 

3.       Trifunctional : - (-T-)  Example : Trimethylol phenol made from phenol and formaldehyde

 



 

The three OH group on the methylol linkage are reactive.


B.      Physical Structure and functionality,

a.       Linear polymers : – Formed from bifunctional group

… -B-B-B-B-B-B-B-B-…

This type of polymer is normally thermoolastic (Creep flow at temperature >150 0 C)



b.      Cross linked polymer : - formed from bi and tri functional groups e.g.a

….B-B-B-B-B-T-B-T-B-….

                 B-B-T-B-T-B-B-B-….



Cross linkage in three dimensions gives elastomeric properties if there are only a few such bond across linear polymer chains.

If bonding is more extensive, solidified thermoset polymers result with high resistance to heat and mechanical deformation

c.       Branched chain polymer: an intermediate case where braches grow from the parent chain with our cross linking.

   B-B-B-

….B-B-T

                  B-B-B-



Branching is caused by small amounts of -T- often as impurities, Present in a bifunctional monomer formulation. The effect is to lower solubility. Increase softening point and reduce thermoplastic forming properties,


 

Location: India

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