Powerpoint presentation

1. Content:
 Polymer
 Behaviour of polymer in solution.
 Definition of molecular weight.
 Effect of moleculer weight in polymer solution.
 Reference and conclution.
4 October 2019 1
Polymer Behaviour in Solution & Effect of Molecular
Weight in Polymer

2. What are Polymers?2
 Polymers are long chain molecules produced by linking small repeat
units (monomers) together
 There are many ways to link different types of monomer to form
polymers
 Polymers exhibit very different physical properties compared to the
monomers, dependent on the length of the polymer chains
Courtesy : sciencedirects.com4 October 2019

3. When a polymer is dissolved in a solvent , different types of interaction exist . The
interaction are discussed below,
Swelling
Swelling of polymer is a slow process involving the penetration of solvent
molecules into the polymer matrix there by increasing its mass and volume.
Polymer chain containing diffused solvent molecules is known as swollen chain.
Behaviour of polymer in solution
4 October 2019 3

4. Cohesive force:
 The cohesive force between chain segments of polymer molecule ,which tightens the polymer coil.
 But when the polymer is dissolve in a solvent a strong interaction between solvent and chain
segment would operate and loosen the polymer coil.
 The polymer molecules are thus more and more expanded as polymer solvent interaction
strengthens.
Polymer coil
Expand Polymer coil
Solvent
Figure courtecy internet
4 October 2019 4

5. Viscosity:
Generally as would be expected the viscosity of polymer solutions increase with increase in
concentration and decrease in temperature. However the opposite behaviour is shown in few cases.
For example , the viscosities of dilute aqueous solution of polymer with ionizable group increases on
further dilution(this is called a polyelectrolyte(repeating unit bear an electrolyte group,Ex polypeptide)
behavior.
Chain Stiffness:
The ratio between the calculated rms end to end distance to the experimental value gives an idea
about stiffness of the chain. For flexible polymer chains ,the ratio is close to 1.0 and rigid chains are
characterized by ratio more than 1.0.
rms
Polymer coil4 October 2019 5

6. Table : chain stiffness ratios for some polymer
Polymer Chain stiffness
Natural rubber 1.1
Polysiobutylene 1.9
Polystyrene 2.4
Polyacrylonitrile 3.0
Cellulose nitrate 4.5
Table data courtecy : Polymer Science by P. Bahadur and N.V. Sastry
4 October 2019 6

7. Behaviour of low-molecular weight polymer in solution
 Dissolution occurs immediately.
 Reaches a saturation line above which no further dissolution occurs.
 Viscocity of solution is similar to that of solvent even at fairly high
concentration of solute.
4 October 2019 7

8. Behaviour of high-molecular weight polymer in solution
• Polymer swells before dissolution begins.
• No saturation limit.
• High viscocities are built up with the increase in polymer
concentration and may prevent further dissolution after certain limit
depending upon the local molecular weight of polymer molecule.
• Very dilute soltion may also be markedly viscous.
4 October 2019 8

9. 9
Molecular Weight
 The molecular weight of a polymer is a way of describing how long the polymer
chains are
 Each monomer has a molecular weight (often called the formula weight)
 Adding the monomers together to make polymers increases the molecular
weight
 The longer the chains, the higher the molecular weight
4 October 2019 9

10. Effect of Molecular Weight on Polymer Properties
Effect of high molecular weight :
High molecular weight increases how far the material can stretch before rupturing. The higher
degree of entanglement allows the material to be pulled further before the chains break.
High molecular weight increases the impact resistance of the material. The higher degree of
entanglement means that in order to rupture, more polymer bonds need to be broken, this means
that the polymer can absorb more energy before failing.
High molecular weight increases the chemical resistance - to a point. It takes more damage to the
main chains of the molecules before it will affect the strength of the material.
High molecular weight increases the viscosity of the material – makes it harder to process the
material using conventional methods. The longer the chains, the harder it is to get them to flow
because they are more tangled.
4 October 2019 10

11. Effect of low molecular weight:
 Low molecular weight polymer act as a plasticizer and soften the polymeric material.
 Low molecular weight polymers have shorter chains which have more end groups that increase
free volume and molecular mobility which makes it easier for the polymer chains to respond to
stresses.
 Polymeric materials consisting of a rather small number of repeat units will be rather soft or even
liquid and will possess little or no strength.
4 October 2019 11

12. Conclution:
 Polymer is macromolecule with million of repeating units.
 Polymer show specific character /behavior in solution such as swelling ,
cohesive force ,viscosity , chain stiffness etc.
 Molecular weight give us idea about how long the polymer chain is.
 High and low molecular weight polymer has several effect which are
discussed previously.
Reference:
We took help from,
Book-Polymer science –P. Bahadur and N.V Sastry
Internet:
www.Wikipedia.com
www.sciencedirect.com
4 October 2019 12

13. Thank you for being with us
4 October 2019 13