polymers for btech 1st year sem 1/2 chemistry

polymers chapter pptx

2. Content
Introduction
Advantages and uses of polymers
Classification of polymers
Mechanism of polymerization
Polymerization techniques
Molecular weight determination
Conducting and biodegradable polymers

3. Introduction
Term“Polymer”derivedfromGreekwordpolus,means
“manymuch”.
Longchainmoleculesformedbyjoiningtogetherof
thousandsofsmallmolecularunitsbychemicalbonds.
Molecularweight10
3
-10
7
Propertiesentirelydifferentfromitsmonomers.
Containsstructuralidentity,repeatingitselfseveral
times.

4. Monomers
Double bond (F=2)
Triple bond (F=4)
Ethylene glycol
HOCH2-CH2OH (F=2)
Lactic acid
CH3CHOHCOOH (F=2)
Tartaric acid
HOOC-CHOH-CHOH-COOH (F=4)
Phenol (max. F=4)
Building blocks of
polymers.
Unite together through
covalent linkages
Functionality(F)≥ 2.
F=2, linear polymer
F ≥3, crosslinked
polymer

5. Examples……….many

8. Cotton fiber is mostly cellulose, and
cellulose is made of chains of the sugar,
glucose linked together a certain way.

9. Monomer Polymer
Isoprene
n
Polyisoprene:
Natural rubber H
3N
O
O
R
Polyamino acid:
protein
H
3N
O
H
N
R
1
O
H
N
R
n+1
O
OH
R
n+2
n
Amino Acid Base
O
OH
OP
O
O
O
oligonucleic acid
DNA
Nucleotide
Base = C, G, T, A
Base
O
O
OP
O
O
O
DNA
DNA

11. Used in:
clothes, shoes,
jackets, belts,
and
accessories. HO N
H
N
H
H
O O
4 4
n
6 carbon
diacid
6 carbon
diamine
Nylon-6,6
+

12. Degree of Polymerization

13. Advantages of polymers over
traditional materials
Resistant to corrosion
Thermal and electrical insulators
Low density hence light weight
Possess elasticity (rubber)
Flexible so easily mouldable into complex shapes
Take variety of colours and shades

14. Uses of polymers
Vehicle parts
Electrical wire covers
Clothes
Furnitures
Matraces
Crockery
Electrical appliances (TV, Radio, Phone body)
Damaged human body organs can be repaired (heart
transplantation)
Coating (adhesives for plywood)
Bottles, buckets, toys, pipes, etc.

15. Classification of polymers
Based on origin:
1.Natural (Cotton, Rubber, Proteins, DNA)
2.Synthetic (PE, PVC, PP, nylon)
3.Semi-synthetic (Nitrocellulose, Cellulose
acetate)
Based on monomer unit:
1.Homo polymer (-AAAAAA-)
2.Copolymer
(Alternate, Block, Random, Graft)

16. On the basis of monomeric unit
Homopolymer Copolymer

17. Graft copolymer
Random copolymer

18. Based on structure/functionality:
1.Linear (HDPE)
2.Branched (LDPE)
3.Cross-linked (PF resin)

19. On the Basis of Structure
•Linear polymers: high m.p., density, tensile strength due
to close packing of polymer chain; e.g. HDPE, nylons,
polyesters
•Branched chain:low m.p., density, tensile strength due to
poor packing of polymer chain; e.g. LDPE, glycogen,
amylopectin
•Three-dimensional: Hard, rigid, brittle, do not melt but
burn on strong heating due to the presence of cross links;
e.g. bakelite, urea-formaldehyde, melamine-formaldehyde

20. Based on thermal response/molecular forces:
1.Thermoplastic (PE, PVC)
2.Thermosets (UF, PF)

21. Thermoplastic Polymers
Linear long chain polymers which can be softened on
heating and hardened on cooling
No cross links between chains.
Weak attractive forces between chains broken by warming.
Change shape -can be remoulded.
Weak forces reform in new shape when cold.
PE, PP, PVC, PS, Teflon, Nylon

22. Thermosetting Polymers
Permanent setting polymers
Three dimensional cross linked structure with strong
covalent bonds
Cannot be reprocessed
Polyester, bakelite, epoxy resins, urea formaldehyde
resin

23. Thermoplastics vs. Thermosetting plastics
Thermoplastics
1.Soften on heating
2.Long chain linear
3.By addition polymerization
4.Can be reshaped and reused
5.Soft weak and less brittle
6.Soluble in org. solvents
7.Reclaimed for wastes
Thermosetting polymers
1.Do not soften on heating
2.3-D structure
3.By condensation
polymerization
4.Can not be reshaped
5.Hard and strong
6.Insoluble in org. solvents.
7.Can not be reclaimed

24. Based on Tacticity(configuration):
1.Isotactic
2.Syndiotactic
3.Atactic

25. On the basis of Tacticity
Depending upon the arrangement of groups above and
below the plane of molecule.

27. Based on polymerization reaction/mode of
reaction:
1.Addition polymerization
2.Condensation polymerization

28. Addition polymerization
Chain growth polymerization
Vinyl polymerization
All the atoms in monomer is used to produce a polymer.

30. Condensation polymerization
Step growth polymerization
Bi-functional or multifunctionalmonomersreact to form
firstdimers, thentrimers, longeroligomers and eventually
long chainpolymers.
E.g: polyesters, polyamides, polyurethanes, etc.

32. Differences between chain-growth polymerization and
step-growth polymerization
Step growth Chain growth
Growth throughout matrix
Rapid loss of monomer early
in the reaction
Average molecular weight
increases slowly at low
conversion and high extents
of reaction are required to
obtain high chain length.
Ends remain active (no
termination)
No initiator necessary
Growth by addition of monomer
only at one end of chain
Some monomer remains even at
long reaction times
Molar mass of backbone chain
increases rapidly at early stage
and remains approximately the
same throughout the
polymerization
Chains not active after
termination
Initiator required

33. Based on end use:
Fibres, Plastics, Elastomers, Films, Resins
Based on conductance:
1.Insulators (mostly all)
2.Conductors (Polyaniline)
Based on environment-friendly nature:
1.Durable
2.Biodegradable

34. Mechanism of polymerization
Cationic polymerization
Anionic polymerization
Free radical polymerization

35. Cationic polymerization
Initiation
Propagation
Termination

36. Continued…………..

37. Continued…………..

38. Continued…………..

39. Continued…………..

40. Continued…………..

41. Anionic Polymerization
Monomerswithe-attractingsubstituents(suchas–
CN,-COOCH
3etc.)inpresenceofsodiumor
potassiumamide.
Initiation mechanism requires the direct transfer of an
electron from the donor to the monomer in order to
form a radical anion.

42. Anionic Polymerization of Styrene

43. …….continued

44. ……continued

45. Continued……………

46. Free radical polymerization
Initiation: active center created.
Radicals from initiators
Transfer to monomer
Types of initiation:
Thermal decomposition
Photolysis
Redoxreactions
Persulfate

47. Continued……………..

48. Continued……………..

49. Continued……………..

51. Polymerization techniques
•Polymerization reactions are exothermic.
•Needs initiator to start the reaction.
Two types:
1. Homogeneous
•Bulk polymerization
•Solution polymerization
2. Heterogeneous
Suspension polymerization
Emulsion polymerization

52. Bulk polymerization
•Polymerization of the undiluted
monomer.
•Carried out by taking monomer in
liquid state and adding a
solubleinitiatorto it.
•Polymerization is carried out in a
bulk polymerization reactor for
controlling the heat of
polymerization
•2 types
Quiescent bulk polymerization
e.g. phenol-formaldehyde
condensation
Stirred bulk polymerization
e.g. nylon 66.

53. Continued……………..
Disadvantage
•Broadm.w.distribution.
•Heattransferandmixingbecomedifficult
astheviscosityofreactionmass
increases.
•Exothermicreaction.
•Thereactionisauto-acceleratedand
sometimesleadstoexplosion.
Duringreaction,themediumbecomes
viscous,diffusibilityofgrowingpolymer
chainbecomesrestricted,probabilityof
chaincollisionbecomesless,termination
becomesdifficult,activeradicalsites
accumulateandrateofpolymerization
increasesenormously
Advantage
Pure polymer with good
insulation properties

54. Solution polymerization
In the presence of solvent.
Heat released absorbed by the solvent, so lesser reaction rate.
After reaction, excess solvent is removed to obtain the pure
polymer.
Good method for applications where the solvent is desired
anyway, as varnish and adhesives.
Not useful for the production of dry polymers because of the
difficulty of complete solvent removal.

56. Continued……………..
Advantages Disadvantages
* Product sometimes * Contamination with solvent
directly usable
* Controlled heat release * Chain transfer to solvent,
leading to low M. W.
* Recycling solvent
* Solvent reduces viscosity, * Environmental pollution due to
making process easier solvent release

57. Suspension (Bead/Pearl) polymerization
Water insoluble monomer is dispersed as large droplets in water
and kept in suspension by mechanical agitation.
Stabilizers as gelatin or cellulose is added.
Initiator (soluble in monomer) is added.
Polymerization starts in each droplet.
Polymer is obtained as pearl or spherical beads.
Polymer isolated through filtration.

58. Continued……………..
Disadvantages
•Applicable only for water
insoluble monomers.
•Difficult to control polymer
(bead) size as reaction is
highly agitation sensitive.
•Polymer purity low due to the
presence of stabilizer in
reaction mixture.
Advantages
Cheap method as water
as solvent is used.
Viscosity increase is
negligible.
Agitation and
temperature control is
easy.
Product insoluble in
water, so separation
becomes easy.

59. Disadvantage
Applicable only for water
insoluble monomers.
Difficult to control polymer
(bead) size as reaction is
highly agitation sensitive.
Polymer purity low due to the
presence of stabilizer in
reaction mixture.
Advantages
Cheap method as water
as solvent is used.
Viscosity increase is
negligible.
Agitation and
temperature control is
easy.
Product insoluble in
water, so separation
becomes easy.

60. Disadvantage
Applicable only for water
insoluble monomers.
Difficult to control polymer
(bead) size as reaction is
highly agitation sensitive.
Polymer purity low due to the
presence of stabilizer in
reaction mixture.

61. Disadvantage
Applicable only for water
insoluble monomers.
Difficult to control polymer
(bead) size as reaction is
highly agitation sensitive.
Polymer purity low due to the
presence of stabilizer in
reaction mixture.

62. Continued……………..
Water
Monomer
Surfactant
Examples:
Synthetic rubber-styrene-
butadiene(SBR), Polybutadiene,
Polychloroprene.
Plastics-PVC, polystyrene,
Acrylonitrile-butadiene-styrene
terpolymer(ABS).
Dispersions-polyvinyl acetate,
polyvinyl acetate copolymers,
latexacrylicpaint, Styrene-butadiene,
VAE

63. Advantages Disadvantages
High molecular
weightpolymers
fast polymerization rates.
allows removal of heat from
the system.
viscosityremains close to
that of water and is not
dependent on molecular
weight.
The final product can be used
as such ,does not need to be
altered or processed
Surfactants and
polymerization adjuvants-
difficult to remove
For dry (isolated) polymers,
water removal is an energy-
intensive process
Designed to operate at high
conversion of monomer to
polymer. This can result in
significantchain transfer to
polymer.
Can not be used for
condensation, ionic or
Ziegler-Natta polymerization.

64. Polymerization Techniques used in the
production of some commercial polymers

65. Vulcanization of Rubber
In order to give strength and
elasticity natural rubber is
vulcanized.
Vulcanisation is a process of treating
natural rubber with sulphur or some
compounds of S under heat as to
modify its properties.
It provides broader useful range (-40
to 100
0
C) than raw rubber(10 to 60
0
C)
Sulphur form cross linked network to
polymer that give mechanical
strength.

66. Recycling Codes for Plastic Resins

67. Continued………….

68. Conducting polymers
Intrinsically conducting:Having extensive conjugation in
the backbone responsible for conductance.
Conducting polymers having conjugation
Doped conducting polymers
Extrinsically conducting: Owe conductivity due to presence
of externally added ingredients in them.
Conducting element filled polymers
Blended conducting polymers

69. Applications of conducting polymers:
In rechargeable batteries
In analytical sensors
For making ion exchangers
In electrochromic displays
In photovoltaic devices