1. 8.1 Introduction
8.2 Heterogeneous Ziegler-Natta polymerization
8.3 Homogeneous Ziegler-Natta polymerization
8.4 Ziegler-Natta copolymerization
8.5 Supported metal oxide catalysts
8.6 Alfin catalysts
8.7 Metathesis polymerization

2. 8.1 Introduction + Karl Ziegler’s discovery ( in Germany-1950s)
at low temperatures and pressures
transition metal compound (Ti, V, Cr) +
ethylene을 중합
Organometallic compound (AlR3)
linear polyethylene (HDPE) – denser, tougher, higher melting
because the more regular structure allows closer chain packing
and a high degree of crystallinity.
HDPE (high-density polyethylene) – bottle, pipe
LDPE (low-density polyethylene) – lap, film, coating
LLDPE (linear low-density polyethylene)
- copolymer of ethylene and 1-butene (Ziegler-type catalysts)
- less energy to produce than LDPE

3. 8.1 Introduction Giulio Natta’s discovery ( in Italy)
polymerizing  - olefins (1-alkenes)
+ catalysts of the type described by Ziegler
Stereoregularity polymer 생성.
(Ziegler & Natta -
1963년 Nobel Prize)
Reduced Metal Oxides
Alfin catalyst
Other complex catalysts.

4. Principal Stereochemistry
TABLE 8.1 Commercially Available Polymers Synthesized with Complex coordination Catalysts
Polymer
Principal
Stereochemistry
Typical Uses
Plastics
Polyethylene, high
density (HDPE)
Polyethylene, ultrahigh
molecular weight
(UHMWPE)
Polypropylene
Poly(1-butene)
Poly(4-methyl-1-
pentene)a
Polystyrene
1,4-Polybutadiene
1,4-Polyisoprene
Ethylene-1-alkeneb
copolymer (linear low-
density polyethylene,
LLDPE)
Ethylene-propylene
block copolymers
(polyallomers)
Polydicyclopentadienec
Bottles, drums, pipe, conduit, sheet,
film, wire and cable insulation
Surgical prostheses, machine
parts, heavy, heavy-duty liners
Automobile and appliance parts,
rope, cordage, webbing, carpeting
film
Film, pipe
Packaging, medical supplies, lighting
Specialty plastics
Metal cam coatings, potting
compounds for transformers
Golf ball covers, orthopedic devices
Blending with LDPE, packaging
film, Bottles
Food packaging, automotive trim,
toys, bottles, film, heat-sterilizable
containers
Reaction injection molding (RIM)
structural plastics -
Isotactic
Syndiotactic
trans

5. Principal Stereochemistry cis trans -
TABLE 8.1 Commercially Available Polymers Synthesized with Complex coordination Catalysts
Polymer
Principal
Stereochemistry
Typical Uses
Tires, conveyer belts, wire and cable
insulation, footware
Tires, footware, adhesives, coated
fabrics
Blending with other elastomers
Molding compounds, engine mounts,
car bumper guards
Asphalt blends, sealants, adhesives,
cable coatings
Impact modifier for polypropylene,
Wire and cable insulation, weather
stripping, tire side walls, hose, seals
cis
trans -
Elastomers
1,4-Polybutadiene
1,4-Polyisoprene
Poly(1-octenylene)
(polyoctenamer)c
Poly(1,3-cyclo-
pentenylene polymer)c
Polypropylene
(amorphous)
Ethylene-propylene
copolymer (EPM, EPR)
Ethylene-propylene-
diene copolymer
(EPDM)
aUsully copolymerized with small amounts of 1-pentene.
b1-Butene, 1-hexene, and 1-octene.
cSynthesized by ring-opening metathesis polymerization of the corresponding cycloaldene.

6. 8.2 Heterogenous Ziegler-Natta Polymerization
8.2.1 Heterogeneous Catalysts
Definition
(1) transition metal compound
( an element from groups Ⅳ to Ⅷ )
- catalyst
- halides or oxyhalides of Ti, V, Cr, Mo, Zr
(2) organometallic compound
( a metal from groups Ⅰ to Ⅲ )
- cocatalyst
- hydrides, alkyls, or aryls of metals
(such as Al, Li, Zn, Sn, Cd, Be, Mg)
Most important from the commercial standpoint
TiCl3
TiCl4
+ R3Al
combination of

7. 8.2 Heterogenous Ziegler-Natta Polymerization
8.2.1 Heterogeneous Catalysts
Catalyst preparation
mixing the components in a dry
inert solvent in the absence of oxygen
usually at a low temperature.
Character of Catalysts
having high reactivity toward many nonpolar monomers.
high degree of stereoregularity.

8. 8.2 Heterogenous Ziegler-Natta Polymerization
8.2.1 Heterogeneous Catalysts
TiCl4-AlR3 (R = alkyl) system – initially exchange reactions
(8.1)
(8.2)
(8.3)
then reduction via homolytic bond cleavage
(8.4)
(8.5)

9. 8.2 Heterogenous Ziegler-Natta Polymerization
8.2.1 Heterogeneous Catalysts
Remove of radicals formed in these reactions
by combination,
disproportionation,
or reaction with solvent.
TiCl3 – formation by the equilibrium
(8.8)

10. 8.2 Heterogenous Ziegler-Natta Polymerization
8.2.1 Heterogeneous Catalysts
Stereochemistry에 영향을 미치는 요인
Better activity is by using TiCl3
TiCl3의 , , ,  form
, ,  : high degree of stereoregularity
 : 40%-50% stereoregularity, 50%-60% – linear structure (atactic polymer)
close-packed layered crystal structures.
stereoregularity is very much dependent
on surface characteristics of the catalyst.
The nature of the transition metal
The alkyl groups of the cocatalyst
The presence of additives.

11. TABLE 8.2. Variation of Polypropylene Isotacticity with Catalysta
Catalystb
Stereoregularity (%)
AlEt3 + TiCl4
AlEt3 + -TiCl3
AlEt3 + -TiCl3
AlEt3 + ZrCl4
AlEt3 + VCl3
AlEt3 + TiCl4 + P, As,
or SB compounds
AlEt2X + TiCl3
AlEtX2 + -TiCl3 + amine 35 45 85 55 73
90-99 99
a Data from Jordan6 and Dawans and Teyssié.7
b Et = ethyl; X = halogen.

12. 8.2 Heterogenous Ziegler-Natta Polymerization
8.2.1 Heterogeneous Catalysts
Problem of Ziegler-Natta catalysts
low efficiency
difficult of catalyst remove
improvement of low efficiency (high-mileage catalysts)
Impregnating the catalyst on a solid support (MgCl2, MgO)
Ex) typical TiCl3-AlR3 catalyst yields
about g/atm,h,g(catalyst) of polyethylene
using a MaCl2-supported catalyst – 7000g/atm,h,g(catalyst)
Activity

13. 8.2.2 Mechanism and Reactivity in Hetrerogeneous Polymerization
A. Two mechanism
a) monometallic mechanism
① Monomer is complexed at a titanium atom exposed
on the catalyst surface by a missing chlorine atom.
② Shifting the vacant octahedral position
③ Insertion reaction
④ Migration of the chain occurs to reestablish the vacant site on the surface.
SCHEME 8.1

14. SCHEME 8.1. Monometallic mechanism of Ziegler-Natta polymerization.

15. 8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization
A. Two mechanism
a) Bimetallic mechanism
Ti 와 monomer가 -complex를 이룬다.
Cyclic transition state가 존재한다.
Ionization
Original form
두 mechanism의 공통점
① Ti atom과 monomer가 -complex를 이룬다.
② Cyclic transition state가 존재한다.
③ Insertion에 의해 중합반응이 진행된다. (stereoregularity 결점)

16. SCHEME 8.2. Bimetallic mechanism of Ziegler-Natta polymerization.

17. 8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization
Ziegler-Natta polymerization – nonpolar monomers사용
monomer activity – decreases with increasing steric hindrance about
the double bond.
reactivity

18. 8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization
Termination
transfer to monomer (8.9 and 8.10)
internal hydride transfer (8.11)
transfer to cocatalyst or to an added alkylmetal compound (8.12)
transfer to added hydrogen (8.13)
(8.9)
(8.10)
(8.11)
(8.12)
(8.13)

19. 8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization
(8.14)
Hydrogen – the preferred transfer agent
because it reacts cleanly,
leaves no residue
low in cost
Molecular weight distributions
insoluble catalyst - broad
soluble catalyst - narrower

20. 8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization
FIGURE 8.1 Types of rate curves observed in Ziegler-Natta polymerization: (A) constant; (B) decay-
ing; and (C) decaying to constant.
Polymerization
rate
Time A B C

21. 8.2.3 Stereochemistry of Heterogeneous Polymerization
insoluble catalysts
Isotactic polymers
level of stereoregularity
– depending, to a degree,
on how exposed the active site is on the catalyst surface.
1-alkenes – approaches from the same side, giving rise to isotactic placement.
double bond of the monomer undergoes cis opening exclusively
cis addition to the double bond occurs

22. 8.2.3 Stereochemistry of Heterogeneous Polymerization
erythro-Diisotactic
threo-Diisotactic
(8.15)
(8.16)
Similar behavior : 1,2-disubstituted olefins.

23. 8.2.4 Polymerization of Dienes
1,3-butadiene : the four possible structures
cis-1,4 ; trans-1,4 ; isotatic 1,2 ; syndiotactic 1,2
TABLE 8.3. Catalysts for the Stereospecific Polymerization of Butadiene
Catalysta
Yield (%)
Polymer
structureb
Ref. no.
R3Al + VCl4
R3Al + VCl3
R3Al + VOCl3
R3Al + TiI4
R2AlCl + CoCl2
R3Al + Ti(OC6H9)4
Et3Al + Cr(C6H5CN)6
Al/Cr = 2
Al/Cr = 10
97-98 99
93-94
96-97
90-100
~100
trans-1,4
cis-1,4
1,2
st-1,2
it-1,2 2 13 14
a Et = ethyl
b st = syndiotactic, it = isotactic.

24. 8.2.4 Polymerization of Dienes
Isoprene
cis- and trans-1,4, 1,2, and 3,4 polymerization
TABLE 8.4. Catalysts for the Stereospecific Polymerization of Isoprene
Catalysta
Yield (%)
Polymer Structure
Ref. No.
R3Al + -TiClB3
Et3Al + VCl3
Et3Al + TiCl4
Al/Ti < 1
Al/Ti > 1
Et3Al + Ti(OR)4 91 99 95 96
trans-1,4
cis-1,4
3,4 15 14
a Et = ethyl

25. 8.2.4 Polymerization of Dienes
Definition of mechanism
whether the catalyst coordinates one(1,2 polymerization)
or both(1,4 polymerization) double bonds of the diene.
2. that coordination of a -allylic structure occurs and
that the direction of approach of monomer determines the structure.
(8.17)
(8.18)

26. 8.2.4 Polymerization of Dienes
(8.19)
(8.20)
Conjugated cyclic dienes : Ziegler-Natta polymerization
Nonconjugated dienes : coordination catalysts 1 2

27. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.1 Metallocene Catalysts
Cp2TiCl2 3
R2AlCl 4 5 6
The earliest metallocene catalysts
MAO – used in conjunction with metallocene catalysts

28. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.1 Metallocene Catalysts
General structure
Examples of catalysts 7
M : Zr, Ti, Hf
X : Cl, alkyl
Z : C(CH3)2, Si(CH3)2, CH2CH2
R : H, alkyl 9 8
Me2Si(Ind)2ZrCl2
Me2C(Flu)(Cp)ZrCl2
form isotactic and syndiotactic polypropylene
usually written in condensed form

29. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.2 Mechanism and Reactivity with Metallocene Catalysts
Difference between metallocene and heterogeneous Ziegler-Natta catalysts
① the former have well-defined molecular structure
② polymerization occurs at one position in the molecule
③ the transition metal atom.
SCHEME Formation of the active site in a zirconocene catalyst. 10 3

30. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.2 Mechanism and Reactivity with Metallocene Catalysts
SCHEME 8.4. Possible polymerization mechanism for ethylene.

31. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.2 Mechanism and Reactivity with Metallocene Catalysts
Character of polymers prepared with metallocene catalysts
① Narrower molecular weight distributions
than those prepared with heterogeneous catalysts.
Better mechanical properties.
③ Polydispersities (Mw/Mn) range from 2to 2.5 for the former,
compared with 5 to 6 for the latter.
④ The molecular weight of the metallocene-based polymers decreases
with increasing polymerization temperature, increasing catalyst concentration,
and addition of hydrogen to the monomer feed.

32. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.2 Mechanism and Reactivity with Metallocene Catalysts
Activities of metallocene catalysts
from 10 to 100 times higher than those of conventional Ziegler-Natta catalysts.
While it is often difficult to correlate structural variables with activity,
the following generalizations can be made :
For the group 4B metals, the order of activity is Zr>Ti>Hf.
Alkyl groups on the cyclopentadiene rings increase catalyst activity if they are
not too bulky. Large, bulky alkyl groups and electron-withdrawing groups decrease
the activity.
Increasing the size of the groups attached to the atom bridging the cyclopentadiene
rings (C or Si) reduces the activity.
MAO affords much higher catalyst activities than ethyl- or higher alkylalumoxane
cocatalysts.

33. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.2 Mechanism and Reactivity with Metallocene Catalysts
Another way that metallocene catalysts differ from eterogeneous catalysts 11
(8.21)
norbornene
high-melting stereoregular polymers

34. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.3 Stereochemistry of Metallocene-Catalyzed Polymerization
Metallocene catalysts exhibit a remarkable ability to control polymer stereochemistry.
Structural variations
synthesis of atactic polypropylene and higher poly(1-alkenes)
isotactic
syndiotatic
type CpZrCl2
atactic polymer
isotactic and syndiotactic polymer 8 9
chiral
achiral

35. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.3 Stereochemistry of Metallocene-Catalyzed Polymerization
The much different sizes of the two pi ligands of 8
assumed to play a role in the formation of symdiotactic polymer
substitution of a methyl group on the cyclopentadiene ring of 9
hemiisotactic polypropylene
(alternate methyls isotactic, the others atactic)

36. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.3 Stereochemistry of Metallocene-Catalyzed Polymerization
Producing polypropylene having alternating atactic and isotactic blocks
Ex)
The zirconium catalyst can rotate between chiral and achiral geometries 12
(8.22)
Thermoplastic elastomers having a range of properties
from a single monomer in a one-pot synthesis

37. 8.3 Homogeneous Ziegler-Natta Polymerization
8.3.3 Stereochemistry of Metallocene-Catalyzed Polymerization
SCHEME 8.5. A mechanism for isotactic placement with a metallocene catalyst.
Optically active isotactic polymer would form from a pure enantiomer of 8

38. 8.4 Ziegler-Natta Copolymerization
(R:aliphatic)
CnH2n+1
n=2일 경우 LLDPE
n=1일 경우 EPDM(EPM)
TABLE 8.5
ethylene is much more reactive than higher alkenes with
both heterogeneous and homogeneous catalysts.
EPDM is prepared with small amounts of a nonconjugated diene to facilitate crosslinking. 13 14 15
Typical dienes
ethylidenenorborene
dicyclopentadiene
1,4-hexadiene

39. TABLE 8.5. Representative Reactivity Ratios in Ziegler-Natta Copolymerizationa
Monomer 1
Monomer 2
Catalystb r1 r2
Heterogeneous
Ethylene
Propylene
Homogeneous
1-Butene
1-Hexene
TiCl3/AlR3
VCl3/AlR3
Cp2ZrMe2
[Z(Ind)2]ZrCl2c
15.72
5.61
26.90
4.04 31
6.6 55 69
0.110
0.145
0.043
0.252
0.005
0.06
0.017
0.02
a Data from Boor3 and Kamisky.22
b R = C6H13; Cp = cyclopentadiene; Me = methyl; Z = bridging group; Ind = indene.
c Z = CH2CH2.

40. 8.5 Supported Metal Oxide Catalysts
Typical supports : Alumina, silica, charcoal (숯)
metals : Cr, V, Mo, Ni, Co, W, Ti etc
Prepare of Catalysts
① The support material is impregnated with the metal ion,
then heated in air at a high temperature to form the metal oxide.
② when the support material is an oxide such as alumina,
the two oxides are coprecipitated and dried in air.
Catalyst is activated
treatment with a reducing agent
(hydrogen, metal hydride, carbon monoxide)
Poisoning of the catalyst
in the presence of water, oxygen, acetylene.

41. 8.5 Supported Metal Oxide Catalysts
(8.23)
Character of the supported metal oxides
① yield polyethylene with approximately equal amounts of
saturated and unsaturated chain ends.
② not as active as Ziegler-Natta catalysts,
and they do not give rise to a high degree of steroregularety.

42. 8.6 Alfin Catalysts alcohol + olefin
effective in polymerizing butadiene and isoprene
to very-high-molecular-weight polymer
The most effective catalyst for diene polymerization
- allylsodium, sodium isopropoxide, sodium chlofide
(8.24)
(8.25)
(8.26)
polymerize butadiene within minutes
to a polymer having a molecular weight of several million

43. 8.7 Metathesis Polymerization
Alkenes undergo a double bond redistribution reaction
(8.27)
(8.28) 16 17

44. 8.7 Metathesis Polymerization
Synthesis of polymers by olefin metathesis
(8.29)
(8.30)
acylic dienes

45. 8.7.1 Ring-Opening Metathesis Polymerization
Propagation steps
(8.31)
That certain group Ⅷ metal compounds
(8.32) 18
7-oxanorbornene derivatives

46. Examples of three metathesis polymerizations
(8.33) 19
(8.34) 20
(8.35) 21
polyoctenamer
norbornene polymer

47. with cyclic polyenes 22
(8.36)
(8.38) 24 23
1—methyl-1,5-cyclooctadiene
cis,trans-cyclodeca-1,5-diene
1,3,5,7-cyclooctatetraene

48. 8.7.2 Acyclic Diene Metathesis Polymerization
ADMET(Acyclic diene metathesis) polymerization of 1,9-decadiene
(8.39)
ADMET is also useful for the synthesis of functionalized polymers.
the symthesis of an unsaturated polymer containing ester functionality.
(8.40)

49. byproduct of ADMET polymerization
8.7.2 Acyclic Diene Metathesis Polymerization
addition of ethylene to an unsaturated polymer can effect depolymerization
byproduct of ADMET polymerization
(8.41)