PolymerChemistry. engineering presentation

polymer chemistry

1. Polymer ChemistryPolymer Chemistry
--------

2. PolymersPolymers
What is a polymer? What is a polymer?
Very Large molecules structures chain-like in Very Large molecules structures chain-like in
nature.nature.
PolyPoly mermer
manymany repeat unitrepeat unit
Adapted from Fig. 14.2, Callister 7e.
CCCCCC
HHHHHH
HHHHHH
Polyethylene (PE)
ClCl Cl
CCCCCC
HHH
HHHHHH
Polyvinyl chloride (PVC)
HH
HHH H
Polypropylene (PP)
CCCCCC
CH
3
HH
CH
3
CH
3
H
repeat
unit
repeat
unit
repeat
unit

3. Ancient Polymer HistoryAncient Polymer History
Originally natural polymers were usedOriginally natural polymers were used
WoodWood – Rubber– Rubber
CottonCotton – Wool– Wool
LeatherLeather – Silk– Silk

4. Polymer CompositionPolymer Composition
Most polymers are hydrocarbonsMost polymers are hydrocarbons
– – i.e. made up of H and Ci.e. made up of H and C
Saturated hydrocarbonsSaturated hydrocarbons
Each carbon bonded to four other atomsEach carbon bonded to four other atoms
CC
nnHH
2n+22n+2
C C
H
H
H
H
H
H

6. Unsaturated HydrocarbonsUnsaturated Hydrocarbons
Double & triple bonds relatively reactive – can form new bondsDouble & triple bonds relatively reactive – can form new bonds
Double bondDouble bond – ethylene or ethene - C – ethylene or ethene - C
nnHH
2n2n
4-bonds, but only 3 atoms bound to C’s4-bonds, but only 3 atoms bound to C’s
CC
H
H
H
H

7. Unsaturated HydrocarbonsUnsaturated Hydrocarbons
Triple bondTriple bond – acetylene or ethyne - C – acetylene or ethyne - C
nnHH
2n-22n-2

CCHH

8. Unsaturated HydrocarbonsUnsaturated Hydrocarbons
An An aromatic hydrocarbonaromatic hydrocarbon (abbreviated (abbreviated
as AH) or as AH) or arenearene is a hydrocarbon, of is a hydrocarbon, of
which the molecular structure incorporates which the molecular structure incorporates
one or more planar sets of six carbon one or more planar sets of six carbon
atoms that are connected by delocalised atoms that are connected by delocalised
electrons numbering the same as if they electrons numbering the same as if they
consisted of alternating single and double consisted of alternating single and double
covalent bonds covalent bonds

9. Unsaturated HydrocarbonsUnsaturated Hydrocarbons
Benzene, C6H6, is the simplest and first Benzene, C6H6, is the simplest and first
recognized aromatic hydrocarbonrecognized aromatic hydrocarbon

10. Unsaturated HydrocarbonsUnsaturated Hydrocarbons
What is actually found is that all of the What is actually found is that all of the
bond lengths in the benzene rings are bond lengths in the benzene rings are
1.397 angstroms1.397 angstroms
This is roughly intermediate between the This is roughly intermediate between the
typical lengths of single bonds (~1.5 typical lengths of single bonds (~1.5
angstroms) and double bonds (~1.3 angstroms) and double bonds (~1.3
angstroms) angstroms)

11. IsomerismIsomerism
IsomerismIsomerism
two compounds with same chemical formula can have two compounds with same chemical formula can have
quite different structures/atomic arrangementquite different structures/atomic arrangement
Ex: CEx: C
88HH
1818
n-octanen-octane
2-methyl-4-ethyl pentane (isooctane)2-methyl-4-ethyl pentane (isooctane)
CCCCCCCCH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H H3CCH2CH2CH2CH2CH2CH2CH3=
H3CCH
CH3
CH2CH
CH
2
CH3
CH3
H3CCH2CH3
( )
6


12. Chemistry of PolymersChemistry of Polymers
Free radical polymerizationFree radical polymerization
InitiatorInitiator: example - benzoyl peroxide: example - benzoyl peroxide
C
H
H
OOC
H
H
C
H
H
O2
CC
HH
HH
monomer
(ethylene)
R+
free radical
RCC
H
H
H
H
initiation
RCC
H
H
H
H
CC
HH
HH
+ RCC
H
H
H
H
CC
HH
HH
propagation
dimer
R= 2

13. Chemistry of PolymersChemistry of Polymers
Adapted from Fig.
14.1, Callister 7e.
Note: polyethylene is just a long HC
- paraffin is short polyethylene

14. Bulk or Commodity PolymersBulk or Commodity Polymers

18. Range of PolymersRange of Polymers
Traditionally, the industry has produced Traditionally, the industry has produced
two main types of synthetic polymer – two main types of synthetic polymer –
plastics and rubbers. plastics and rubbers.
Plastics are (generally) rigid materials at Plastics are (generally) rigid materials at
service temperatures service temperatures
Rubbers are flexible, low modulus Rubbers are flexible, low modulus
materials which exhibit long-range materials which exhibit long-range
elasticity.elasticity.

19. Range of PolymersRange of Polymers
Plastics are further subdivided into Plastics are further subdivided into
thermoplastics and thermosetsthermoplastics and thermosets

20. Range of PolymersRange of Polymers

22. Range of PolymersRange of Polymers
Another way of classifying polymers is in Another way of classifying polymers is in
terms of their form or functionterms of their form or function

23. Synthesis of Synthesis of
PolymersPolymers

24. Synthesis of PolymersSynthesis of Polymers
There are a number different methods There are a number different methods
of preparing polymers from suitable of preparing polymers from suitable
monomers, these are monomers, these are
step-growth (or condensation) step-growth (or condensation)
polymerisationpolymerisation
addition polymerisationaddition polymerisation
insertion polymerisation.insertion polymerisation.

25. Types of PolymerizationTypes of Polymerization
Chain-growth polymers, also known as
addition polymers, are made by chain
reactions

26. Types of PolymerizationTypes of Polymerization
Step-growth polymers, also called
condensation polymers, are made by
combining two molecules by removing a
small molecule

27. Addition Vs. Condensation Addition Vs. Condensation
PolymerizationPolymerization
Polymerisation reactions can generally be Polymerisation reactions can generally be
written aswritten as
x-mer + y-mer x-mer + y-mer (x +y)-mer(x +y)-mer
In a reaction that leads to In a reaction that leads to condensation condensation
polymerspolymers, x and y may assume any value, x and y may assume any value
i.e. chains of any size may react together i.e. chains of any size may react together
as long as they are capped with the as long as they are capped with the
correct functional groupcorrect functional group

28. Addition Vs. Condensation Addition Vs. Condensation
PolymerizationPolymerization
In In addition polymerizationaddition polymerization although x although x
may assume any value, y is confined to may assume any value, y is confined to
unityunity
i.e. the growing chain can react only with a i.e. the growing chain can react only with a
monomer molecule and continue its monomer molecule and continue its
growthgrowth

29. ThermodynamicsThermodynamics
Thermodynamics of polymerization Thermodynamics of polymerization
determines the position of the equilibrium determines the position of the equilibrium
between polymer and monomer(s).between polymer and monomer(s).
The well known thermodynamic The well known thermodynamic
expression:expression:
G = G = H - TH - TSS
yields the basis for understanding yields the basis for understanding
polymerization/depolymerization behavior.polymerization/depolymerization behavior.

30. ThermodynamicsThermodynamics
For polymerization to occur (i.e., to be For polymerization to occur (i.e., to be
thermodynamically feasible), the Gibbs thermodynamically feasible), the Gibbs
free energy of polymerization free energy of polymerization GG
pp < 0 < 0. .

If If GG
p p > 0> 0, then depolymerization will be , then depolymerization will be
favored.favored.

31. ThermodynamicsThermodynamics
Standard enthalpy and entropy changes, Standard enthalpy and entropy changes,
HH
oo
p and p and SS
oo
p are reported for reactants p are reported for reactants
and products in their appropriate standard and products in their appropriate standard
states. Generally:states. Generally:
Temperature = 25Temperature = 25
oo
C = 298KC = 298K
Monomer – pure, bulk monomer or 1 M Monomer – pure, bulk monomer or 1 M
solutionsolution
Polymer – solid amorphous or slightly Polymer – solid amorphous or slightly
crystallinecrystalline

32. ThermodynamicsThermodynamics
Polymerization is an association reaction Polymerization is an association reaction
such that many monomers associate to such that many monomers associate to
form the polymer form the polymer
Thus: Thus: Sp < 0 for nearly all polymerization Sp < 0 for nearly all polymerization
processesprocesses

33. ThermodynamicsThermodynamics
Since depolymerization is almost always Since depolymerization is almost always
entropicallyentropically favored, the favored, the HH
pp must then be must then be
sufficiently sufficiently negativenegative to compensate for the to compensate for the
unfavorable entropic term. unfavorable entropic term.

Only then will polymerization be Only then will polymerization be
thermodynamically favored by the thermodynamically favored by the
resulting negative resulting negative Gp. Gp.

34. ThermodynamicsThermodynamics
In practice:In practice:
Polymerization is favored at low Polymerization is favored at low
temperatures: Ttemperatures: TSp is smallSp is small
Depolymerization is favored at high Depolymerization is favored at high
temperatures: Ttemperatures: TSp is largeSp is large

35. ThermodynamicsThermodynamics
Therefore, thermal instability of polymers Therefore, thermal instability of polymers
results when results when TTSS
pp overrides overrides HH
pp and thus and thus
GG
pp > O > O; this causes the system to ; this causes the system to
spontaneously depolymerize (spontaneously depolymerize (if kinetic if kinetic
pathway existspathway exists).).

36. ThermodynamicsThermodynamics
the activation energy for the the activation energy for the
depropagation reaction is higher,depropagation reaction is higher,
Compared to the propagation reaction its Compared to the propagation reaction its
rate increases more with increasing rate increases more with increasing
temperature temperature
 As shown below, this results in a ceiling As shown below, this results in a ceiling
temperature.temperature.

37. ThermodynamicsThermodynamics
ceiling temperature ceiling temperature
the temperature at which the propagation and the temperature at which the propagation and
depropagation reaction rates are exactly depropagation reaction rates are exactly
equal at a given monomer concentrationequal at a given monomer concentration
300350400450500550600
0
1
2
3
4
5
6
T
c
k
p
[M] - k
dp
k
p
[M]
k
dp
k
,

s
e
c
-
1
Temperature,
o
K

38. ThermodynamicsThermodynamics
At long chain lengths, the chain At long chain lengths, the chain
propagation reaction propagation reaction
is characterized by the following is characterized by the following
equilibrium expression:equilibrium expression:
+M
k
p
kdp
P
n
* *
P
n+1
k
k M
p
dp c





[P]
[P][M]
n1
*
n
*
1
[]

39. ThermodynamicsThermodynamics
The standard-state enthalpy and entropy The standard-state enthalpy and entropy
of polymerization are related to the of polymerization are related to the
standard-state monomer concentration, standard-state monomer concentration,
[M][M]
oo (usually neat liquid or 1 M solution) as (usually neat liquid or 1 M solution) as
follows:follows:
 GHTSRT
o o
  ln
[]
[]
M
M
o

40. ThermodynamicsThermodynamics
At equilibrium, At equilibrium, G = 0, and T = TG = 0, and T = T
cc
(assuming that (assuming that HH
pp
oo
and and SS
pp
oo
are are
independent of temperature). independent of temperature).
Or:Or:
 HTS RT
[M]
[M]
o
c
o
c
o
c
 ln
T
H
SRln
[M]
[M]
c
o
o c
o





41. ThermodynamicsThermodynamics
Or:Or:
ln
[M]
[M]
H
RT
S
R
c
o
o
c
o
 
 

42. ThermodynamicsThermodynamics
At [M]At [M]
cc = [M] = [M]
oo, T, T
cc = = HH
pp
oo
//SS
pp
oo

Specific Examples of Monomer - Polymer Equilibrium
kcal/mol cal/mol-deg (H/S)
Monomer Hp Sp Tc(
o
C)
Ethylene -21.2 -24 610
Isobutylene -12.9 -28 175
Styrene -16.7 -25.0 395
-methyl styrene -8.4 -24 66
2,4,6-trimethyl styrene -16.7 --- ---
TFE -37 -26.8 1100

43. ThermodynamicsThermodynamics
Notice the large variation in the -Notice the large variation in the -H H
values.values.
ethylene > isobutylene - attributed to steric hinderance ethylene > isobutylene - attributed to steric hinderance
along the polymer chain, which decreases the along the polymer chain, which decreases the
exothermicity of the polymerization reaction.exothermicity of the polymerization reaction.
ethylene > styrene > ethylene > styrene > -metylstyrene - also due to -metylstyrene - also due to
increasing steric hinderance along the polymer chain.increasing steric hinderance along the polymer chain.
Note, however, that 2,4,6-trimethylstyrene has the Note, however, that 2,4,6-trimethylstyrene has the
same -same -H value as styrene. Clearly, the major effect H value as styrene. Clearly, the major effect
occurs for substituents directly attached to the polymer occurs for substituents directly attached to the polymer
backbone.backbone.

44. Types of Addition Types of Addition
PolymerizationPolymerization
Free RadicalFree Radical
CationicCationic
AnionicAnionic

45. Free Radical PolymerizationFree Radical Polymerization
Usually, many low molecular weight Usually, many low molecular weight
alkenes undergo rapid polymerization alkenes undergo rapid polymerization
reactions when treated with small amounts reactions when treated with small amounts
of a radical initiator. of a radical initiator.
For example, the polymerization of For example, the polymerization of
ethylene ethylene

46. Free Radical PolymerizationFree Radical Polymerization

47. Free Radical PolymerizationFree Radical Polymerization

48. Free Radical PolymerizationFree Radical Polymerization

49. Thermodynamic considerations for Thermodynamic considerations for
the free radical polymerization the free radical polymerization

50. Thermodynamic considerations for Thermodynamic considerations for
the free radical polymerization the free radical polymerization
Chain growthChain growth
Activation energy for chain growth much Activation energy for chain growth much
lower than for initiation.lower than for initiation.
i.e. Growth velocity less temperature i.e. Growth velocity less temperature
dependent than initiation dependent than initiation

51. Thermodynamic considerations for Thermodynamic considerations for
the free radical polymerization the free radical polymerization

52. Thermodynamic considerations for Thermodynamic considerations for
the free radical polymerization the free radical polymerization

53. Macromonomer/Comonomer Macromonomer/Comonomer
Copolymerization Kinetics : free radicalCopolymerization Kinetics : free radical
In such copolymerizations, owing to the large differences in
molar mass between Macromonomer M and Comonomer A, the
monomer concentration is always very small : consequently the
classical instantaneous copolymerization equation
][]([r][
][][]([
][d
][d
M AMM
MArA
M
A
a



Reduces to
][
][
][d
][d
M
Ar
M
A
a

As in an «
 ideal » copolymerization the reciprocal of the radical reactivity
of the comonomer is a measure of the macromonomer to take part in the
process
Controlled Free Radical Copolymerization

54. Ionic PolymerizationIonic Polymerization
Ionic polymerization is more complex than Ionic polymerization is more complex than
free-radical polymerization free-radical polymerization

55. Ionic PolymerizationIonic Polymerization
Whereas free radical polymerization is Whereas free radical polymerization is
non-specific, the type of ionic non-specific, the type of ionic
polymerization procedure and catalysts polymerization procedure and catalysts
depend on the nature of the substituent depend on the nature of the substituent
(R) on the vinyl (ethenyl) monomer.(R) on the vinyl (ethenyl) monomer.

56. Ionic PolymerizationIonic Polymerization
Cationic initiation is therefore usually Cationic initiation is therefore usually
limited to the polymerization of monomers limited to the polymerization of monomers
where the R group is electron-donating where the R group is electron-donating
This helps stabilise the delocation of the This helps stabilise the delocation of the
positive charge through the p orbitals of positive charge through the p orbitals of
the double bondthe double bond

57. Ionic PolymerizationIonic Polymerization
Anionic initiation, requires the R group to Anionic initiation, requires the R group to
be electron withdrawing in order to be electron withdrawing in order to
promote the formation of a stable promote the formation of a stable
carbanion (ie, -M and -I effects help carbanion (ie, -M and -I effects help
stabilise the negative charge).stabilise the negative charge).

58. Ionic PolymerizationIonic Polymerization

59. Ionic PolymerizationIonic Polymerization

60. Ionic PolymerizationIonic Polymerization
M is a Monomer Unit. M is a Monomer Unit.
As these ions are associated with a As these ions are associated with a
counter-ion or gegen-ion the solvent has counter-ion or gegen-ion the solvent has
important effects on the polymerization important effects on the polymerization
procedure.procedure.

61. Ionic PolymerizationIonic Polymerization
(ii) Chain Propagation depends on :(ii) Chain Propagation depends on :
 Ion separationIon separation
The nature of the SolventThe nature of the Solvent
Nature of the counter IonNature of the counter Ion

62. Anionic PolymerizationAnionic Polymerization
Involves the polymerization of monomers Involves the polymerization of monomers
that have strong electron-withdrawing that have strong electron-withdrawing
groups, eg, acrylonitrile, vinyl chloride, groups, eg, acrylonitrile, vinyl chloride,
methyl methacrylate, styrene etc. The methyl methacrylate, styrene etc. The
reactions can be initiated by methods (b) reactions can be initiated by methods (b)
and (c) as shown in the sheet on ionic and (c) as shown in the sheet on ionic
polymerizationpolymerization

63. Anionic PolymerizationAnionic Polymerization
eg, for mechanism (b)eg, for mechanism (b)

64. Anionic PolymerizationAnionic Polymerization
The gegen-ion may be inorganic or The gegen-ion may be inorganic or
organic and typical initiators include organic and typical initiators include
KNH2, n-BuLi, and Grignard reagents KNH2, n-BuLi, and Grignard reagents
such as alkyl magnesium bromidessuch as alkyl magnesium bromides

65. Anionic PolymerizationAnionic Polymerization
If the monomer has only a weak electron-If the monomer has only a weak electron-
withdrawing group then a strong base withdrawing group then a strong base
initiator is required, eg, butyllithium; for initiator is required, eg, butyllithium; for
strong electron-withdrawing groups only a strong electron-withdrawing groups only a
weak base initiator is required, eg, a weak base initiator is required, eg, a
Grignard reagent. Grignard reagent.

66. Anionic PolymerizationAnionic Polymerization
Initiation mechanism (c) requires the direct Initiation mechanism (c) requires the direct
transfer of an electron from the donor to transfer of an electron from the donor to
the monomer in order to form a radical the monomer in order to form a radical
anion. anion.
This can be achieved by using an alkali This can be achieved by using an alkali
metal eg.,metal eg.,

67. Anionic Polymerization of StyreneAnionic Polymerization of Styrene

68. Anionic Polymerization of StyreneAnionic Polymerization of Styrene

69. Anionic Polymerization of StyreneAnionic Polymerization of Styrene

70. Anionic Polymerization of StyreneAnionic Polymerization of Styrene

71. Anionic Polymerization of StyreneAnionic Polymerization of Styrene
The activation energy for transfer is larger than
for propagation, and so the chain length
decreases with increasing temperature.

72. Anionic KineticsAnionic Kinetics
A general description of the kinetics is A general description of the kinetics is
complicated however some useful complicated however some useful
approximations may be attained.approximations may be attained.

73. Anionic Kinetics Anionic Kinetics —— approximations approximations
1.1.The rate of polymerization will be proportional The rate of polymerization will be proportional
to the product of the monomer concentration of to the product of the monomer concentration of
growing chain ends.growing chain ends.
2.2.Under conditions of negligible association each Under conditions of negligible association each
initiator molecule will start a growing chaininitiator molecule will start a growing chain
3.3.In the absence of terminating impurities the In the absence of terminating impurities the
number of growing chain ends will always equal number of growing chain ends will always equal
the number of initiator molecules addedthe number of initiator molecules added

74. Anionic KineticsAnionic Kinetics
1.1.If propagation is rate controlingIf propagation is rate controling
 (11-1)(11-1)

0IMk
dt
Md
r
pp 



75. Anionic KineticsAnionic Kinetics
2.2.In BuLi polymerization at high In BuLi polymerization at high
concentrations in non polar solvents, the concentrations in non polar solvents, the
chain ends are present almost exclusively chain ends are present almost exclusively
as inactive dimmers, which dissociate as inactive dimmers, which dissociate
slightly according to the equilibriumslightly according to the equilibrium
 

 LiBuMLiBuM
x
k
x
2
2

76. Anionic KineticsAnionic Kinetics
Where K=Where K=
3.3.The concentration of active chain ends is The concentration of active chain ends is
thenthen
(11-3)(11-3)
Now it takes two initiator molecules to Now it takes two initiator molecules to
make one inactive chain dimmer, somake one inactive chain dimmer, so
(11-4)(11-4)
   1/
2
2


LiBuMLiBuM
xx
    
2/1
2
2
1

 LiBuMKLiBuM
xx
  

22
0
2
IBuLi
LiBuM
x



77. Anionic KineticsAnionic Kinetics
The rate of polymerisation then becomesThe rate of polymerisation then becomes
(11-5)(11-5)
The low value of K, reflecting the presence of most chain The low value of K, reflecting the presence of most chain
ends in the inactive association state, gives rise to the ends in the inactive association state, gives rise to the
low rates of polymerisation in nonpolar solvents. At very low rates of polymerisation in nonpolar solvents. At very
high concentrations, association may be even greater high concentrations, association may be even greater
and the rate essentially independent of [Iand the rate essentially independent of [I
00]]
 
2/1
02/1
2









I
Kk
dt
Md
r
pp

78. Cationic PolymerizationCationic Polymerization

79. Cationic PolymerizationCationic Polymerization
(ii) PropagationChain growth takes place (ii) PropagationChain growth takes place
through the repeated addition of a through the repeated addition of a
monomer in a head-to-tail manner to the monomer in a head-to-tail manner to the
ion with retention of the ionic character ion with retention of the ionic character
throughoutthroughout

80. Cationic PolymerizationCationic Polymerization

81. Cationic PolymerizationCationic Polymerization
(iii) Termination(iii) Termination
Termination of cationic polymerization Termination of cationic polymerization
reactions are less well-defined than in reactions are less well-defined than in
free-radical processes. Two possibilities free-radical processes. Two possibilities
exist as follows:exist as follows:

82. Cationic PolymerizationCationic Polymerization

83. Cationic PolymerizationCationic Polymerization
Hydrogen abstraction occurs from the Hydrogen abstraction occurs from the
growing chain to regenerate the catalyst-growing chain to regenerate the catalyst-
co-catalyst complex. co-catalyst complex.
Covalent combination of the active centre Covalent combination of the active centre
with a catalyst-co-catalyst complex with a catalyst-co-catalyst complex
fragment may occur giving two inactive fragment may occur giving two inactive
species. species.

84. Cationic PolymerizationCationic Polymerization
The kinetic chain is terminated and the The kinetic chain is terminated and the
initiator complex is reduced - a more initiator complex is reduced - a more
effective route to reaction termination.effective route to reaction termination.

85. Cationic PolymerizationCationic Polymerization

86. Cationic PolymerizationCationic Polymerization
The kinetics of these reactions is not well The kinetics of these reactions is not well
understood, but they proceed very rapidly understood, but they proceed very rapidly
at extremely low temperatures.at extremely low temperatures.

87. Polymerization Processes
TWO USEFUL DISTINCTIONS ;
BETWEEN BATCH AND CONTINUOUS
AND BETWEEN SINGLE - PHASE AND
MULTI -PHASE
SINGLE - PHASE
Bulk or Melt Polymerization
Solution Polymerization

88. Polymerization Processes

89. Bulk PolymerizationBulk Polymerization
The simplest techniqueThe simplest technique
Gives the highest-purity polymerGives the highest-purity polymer
Only monomer, a monomer soluble Only monomer, a monomer soluble
initiator and perhaps a chain transfer initiator and perhaps a chain transfer
agent are usedagent are used
This process can be used for many free This process can be used for many free
radical polymerizations and some step-radical polymerizations and some step-
growth (condensation) polymerisation.growth (condensation) polymerisation.

90. Polymerization TechniquesPolymerization Techniques
These include:These include:
Bulk PolymerizationBulk Polymerization
Solution PolymerizationSolution Polymerization
Suspension PolymerizationSuspension Polymerization
Emulsion PolymerizationEmulsion Polymerization

91. Bulk PolymerizationBulk Polymerization
Advantages:Advantages:
High yield per reactor volume High yield per reactor volume
Easy polymer recoveryEasy polymer recovery
The option of casting the polymerisation The option of casting the polymerisation
mixture into final product formmixture into final product form

92. Bulk PolymerizationBulk Polymerization
Limitations:Limitations:
Difficulty in removing the last traces of Difficulty in removing the last traces of
monomermonomer
The problem of dissipating heat produced The problem of dissipating heat produced
during the polymerizationduring the polymerization
In practice, heat dissipated during bulk In practice, heat dissipated during bulk
polymerization can be improved by providing polymerization can be improved by providing
special baffles special baffles

93. Solution PolymerizationSolution Polymerization
Definition:Definition: A polymerization process in A polymerization process in
which the monomers and the which the monomers and the
polymerization initiators are dissolved in a polymerization initiators are dissolved in a
nonmonomeric liquid solvent at the nonmonomeric liquid solvent at the
beginning of the polymerization reaction. beginning of the polymerization reaction.
The liquid is usually also a solvent for the The liquid is usually also a solvent for the
resulting polymer or copolymer. resulting polymer or copolymer.

94. Solution PolymerizationSolution Polymerization
Heat removed during polymerization can Heat removed during polymerization can
be facilitated by conducting the be facilitated by conducting the
polymerization in an organic solvent or polymerization in an organic solvent or
waterwater

95. Solution PolymerizationSolution Polymerization
Solvent Requirements:Solvent Requirements:
Both the initiator and the monomer be Both the initiator and the monomer be
soluble in it soluble in it
The solvent have acceptable chain The solvent have acceptable chain
transfer characteristics and suitable transfer characteristics and suitable
melting and boiling points for the melting and boiling points for the
conditions of the polymerization and conditions of the polymerization and
subsequent solvent-removal step.subsequent solvent-removal step.

96. Solution PolymerizationSolution Polymerization
Solvent choice may be influenced by other Solvent choice may be influenced by other
factors such as flash point, cost and factors such as flash point, cost and
toxicitytoxicity
Reactors are usually stainless steel or Reactors are usually stainless steel or
glass linedglass lined

97. Solution PolymerizationSolution Polymerization
Disadvantages:Disadvantages:
small yield per reactor volume small yield per reactor volume
The requirements for a separate solvent The requirements for a separate solvent
recovery steprecovery step

98. Suspension PolymerizationSuspension Polymerization
Definition:Definition: A polymerization process in A polymerization process in
which the monomer, or mixture of which the monomer, or mixture of
monomers, is dispersed by mechanical monomers, is dispersed by mechanical
agitation in a liquid phase, usually water, agitation in a liquid phase, usually water,
in which the monomer droplets are in which the monomer droplets are
polymerized while they are dispersed by polymerized while they are dispersed by
continuous agitation. Used primarily for continuous agitation. Used primarily for
PVC polymerizationPVC polymerization

99. Suspension PolymerizationSuspension Polymerization
If the monomer is insoluble in water, bulk If the monomer is insoluble in water, bulk
polymerization can be carried out in polymerization can be carried out in
suspended droplets, i.e., monomer is suspended droplets, i.e., monomer is
mechanically dispersed. mechanically dispersed.
The water phase becomes the heat The water phase becomes the heat
transfer medium. transfer medium.

100. Suspension PolymerizationSuspension Polymerization
So the heat transfer is very good. In this So the heat transfer is very good. In this
system, the monomer must be either system, the monomer must be either
1) insoluble in water or 1) insoluble in water or
2) only slightly soluble in water, so that when 2) only slightly soluble in water, so that when
it polymerizes it becomes insoluble in water.it polymerizes it becomes insoluble in water.

101. Suspension PolymerizationSuspension Polymerization
The behavior inside the droplets is very The behavior inside the droplets is very
much like the behavior of bulk much like the behavior of bulk
polymerization polymerization
Since the droplets are only 10 to 1000 Since the droplets are only 10 to 1000
microns in diameter, more rapid reaction microns in diameter, more rapid reaction
rates can be tolerated (than would be the rates can be tolerated (than would be the
case for bulk polymerization) without case for bulk polymerization) without
boiling the monomer. boiling the monomer.

102. Emulsion PolymerizationEmulsion Polymerization
Emulsion polymerizationEmulsion polymerization is a type of is a type of
radical polymerization that usually starts radical polymerization that usually starts
with an emulsion incorporating water, with an emulsion incorporating water,
monomer, and surfactant. monomer, and surfactant.

103. Emulsion PolymerizationEmulsion Polymerization
The most common type of emulsion The most common type of emulsion
polymerization is an oil-in-water emulsion, polymerization is an oil-in-water emulsion,
in which droplets of monomer (the oil) are in which droplets of monomer (the oil) are
emulsified (with surfactants) in a emulsified (with surfactants) in a
continuous phase of water. continuous phase of water.
Water-soluble polymers, such as certain Water-soluble polymers, such as certain
polyvinyl alcohols or hydroxyethyl polyvinyl alcohols or hydroxyethyl
celluloses, can also be used to act as celluloses, can also be used to act as
emulsifiers/stabilizers.emulsifiers/stabilizers.

104. Emulsion Polymerization – SchematicEmulsion Polymerization – Schematic

105. Emulsion PolymerizationEmulsion Polymerization
Advantages of emulsion polymerization include:Advantages of emulsion polymerization include:
High molecular weight polymers can be made at High molecular weight polymers can be made at
fast polymerization rates. By contrast, in bulk and fast polymerization rates. By contrast, in bulk and
solution free radical polymerization, there is a solution free radical polymerization, there is a
tradeoff between molecular weight and tradeoff between molecular weight and
polymerization rate.polymerization rate.
The continuous water phase is an excellent The continuous water phase is an excellent
conductor of heat and allows the heat to be conductor of heat and allows the heat to be
removed from the system, allowing many removed from the system, allowing many
reaction methods to increase their rate.reaction methods to increase their rate.

106. Emulsion PolymerizationEmulsion Polymerization
Advantages Continued:Advantages Continued:
Since polymer molecules are contained Since polymer molecules are contained
within the particles, viscosity remains within the particles, viscosity remains
close to that of water and is not dependent close to that of water and is not dependent
on molecular weight.on molecular weight.
The final product can be used as is and The final product can be used as is and
does not generally need to be altered or does not generally need to be altered or
processed.processed.

107. Emulsion PolymerizationEmulsion Polymerization
Disadvantages of emulsion polymerization include:Disadvantages of emulsion polymerization include:
For dry (isolated) polymers, water removal is an For dry (isolated) polymers, water removal is an
energy-intensive processenergy-intensive process
Emulsion polymerizations are usually designed Emulsion polymerizations are usually designed
to operate at high conversion of monomer to to operate at high conversion of monomer to
polymer. This can result in significant chain polymer. This can result in significant chain
transfer to polymer.transfer to polymer.

108. Fabrication methodsFabrication methods

113. ExampleExample
Suggest a polymer and fabrication process
suitable to produce the following items.
Support your choice by contrasting it with
other possible alternatives.
Car bumper
Carry bag
Machine gear
Shower curtain
Tooth brush stand

114. SolutionSolution
i) Car bumper
Polyurethane is one of the suitable materials for car
bumpers. another suitable material is PP. Reaction
injection molding process is suitable to produce
polyurethane bumpers. Polyurethane is molded by
mixing of highly reactive liquids (isocyanateandpolyol).
Because the materials are very reactive liquids, Other
molding processes such as injection molding and
compression molding can not be used for this purpose.
However, injection molding and compression molding
methods can be used to make PP bumpers.

115. SolutionSolution
ii) Carry bag
Polyethylene (PE)is used widely for making
carry bags. Blown film extrusion methodis best
suitable to produce carry bags. Calendering
method also can be applied for the same
purpose. However, considering the production
rate and thickness range that can be produced,
blown film extrusion method is ideal to produce
carry bags.