Polymer Chemistry
Guangxi University School of Chemistry & Chemical Engineerin
g
Li Guang Hua (李光华)
Lab:材料楼—409#,321# E-mail : [email protected] phone: 15978133590
CHAPTER 5
1. Introduction
Coordination Polymerization:
2. Heterogeneous Ziegler-Natta Polymerization2.1 Heterogeneous Catalysts2.2 Polymerization of α-olefin2.3 Polymerization of Diene
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2.3 Polymerization of Diene
3. Homogeneous Ziegler-Natta Polymerization3.1 Metallocene Catalysts3.2 Mechanism
4. Supported Metal Oxide Catalysts
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1. INTRODUCTION (I)
CH2 CH2n CH2 CH2 nR PZN
High T & Plow density PE (LDPE)
CH2 CH
CH3
n R PZNor ionic PZN
Oligomer
Both ethylene and propylene are polymerizable monomers
(branched structure)
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Both ethylene and propylene are polymerizable monomers thermodynamically.
In 1953, Karl Ziegler (GER) discoveredØ
CH2 CH2n + Al(C2H5)3 TiCl4 CH2 CH2 nlow T & P
high density PE (HDPE)(linear structure)
catalystcocatalyst
In 1954, Giulio Natta (ITA) discoveredØ
CH2 CHn + Al(C2H5)3 TiCl3CH3
CH2 CH nCH3
low T & P
isotactic PP (i-PP)catalystcocatalyst
1. INTRODUCTION (II)
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In 1959, Natta proposed bimetallic mechanism.
In 1960, Cossee-Arlman proposed monometallic mechanism.
Monometallic mechanism is favored in heterogeneous processes.
1. INTRODUCTION (III)
TiR
RAl
Ø Bimetallic mechanism (1959)
Active speciesCH2 CH
X
TiR
RAl
δδ
δ δ
TiR
RAl
CH2 CH
X
CH2=CHX
coordination complexation
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Ti RR Al
CH2 CH
X
Six-membered cyclictransition state
TiR
Al
R
CH2
CH X
δδ
TiR
Al
R
CH2
CH X
Insertion to Al-C bond
1. INTRODUCTION (IV)
Ø Monometallic mechanism (1960)
Active species
CH2=CHX
Coordination Four-membered cyclictransition state
Ti
R
ClCl
Cl
ClTi
R
ClCl Cl
Cl C
C
H H
X H
Ti
R
ClCl Cl
Cl C
C
H H
X H
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transition state
Insertion to Ti-C bond
Ti
R
ClCl Cl
ClCH2
CH
XTi
R
ClCl Cl
ClCH2
CH X
migration of the chain
Ti
R
ClCl Cl
Cl C
C
H H
X H
1. INTRODUCTION (V)
TiR
RAl
CH2 CH
X
Coordination
Determine to insert the direction of monomers
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Stereoregular polymer (立构规整聚合物)
Coordination PZN or complexing PZN Insertion PZN orStereoregular PZN (定向聚合)
â Ziegler and Natta shared the Nobel Prize in Chemistry in 1963.
1. INTRODUCTION (VI)
Feature of coordination PZN:
¹ Reaction is of anionic nature
¹ Monomer coordinates with a transition metal to form σ-πcomplex
¹ Polymer chain grows by successive insertion reactionsof complex monomers
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¹ Can form stereoregular polymers (but also atactic polymers)
Heterogeneous PZNHomogeneous PZNCoordination PZN
2. HETEROGENEOUS Z-N PZN (I)
Heterogeneous catalystsFZiegler-Natta catalyst :
IV ~ VIII transition metal compound
IA ~ IIIA organometallic compound
(catalyst)
(cocatalyst)
ex., Ti, V, Cr, Mn, Fe, Co, Nipost transition metal
Ø
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IA ~ IIIA organometallic compoundex., AlR3, AlR2X
TiCl4 + AlR3 R3AlCl TiCl3Provide vacant sites
TiCl3 + AlR3
α, δ,γ, and β form
High degree of stereoregularityAtactic polymer
Catalyst Stereoregularity (%)
AlEt3 + TiCl4 35AlEt3 + β-TiCl3 45AlEt + α-TiCl 85
Variation of polypropylene isotacticity with catalyst
PZN of α-olefinsF
2. HETEROGENEOUS Z-N PZN (II)
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AlEt3 + α-TiCl3 85AlEt3 + ZrCl4 55AlEt3 + VCl3 73AlEt2X + TiCl3 90–99AlEtX2 + γ-TiCl3 +amine 99
Two components
Three components
Lewis base(Electron donor)
2AlEtX2 + NR3 AlEt2X + NR3AlX3
¹ First generation catalysts of PP (1950s-60s)
Catalyst Stereoregularity (%) Efficiency (g PP/g Ti)
AlEt3 + α-TiCl3 85 5×103
¹ Second generation catalysts of PP (1960s)
2. HETEROGENEOUS Z-N PZN (III)
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Catalyst Stereoregularity(%)
Efficiency (g PP/g Ti)
AlEt3 + α-TiCl3 + HMPTA ~ 90 5×104
HMPTA : hexamethylphosphorictriamide (六甲基磷酰三胺)
P[N(CH3)2]3=O
¹ Third generation catalysts of PP (1970s-80s)
Catalyst Stereoregularity(%)
Efficiency (g PP/g Ti)
AlEt3 + α-TiCl3 + esterssupported on MgCl2
> 98 2.4×106
2. HETEROGENEOUS Z-N PZN (IV)
MgCl2
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Eliminated the need for the costly step of removing catalyst from the product.
••• ••
• ••
••••
••••••••
•
•••••
••••
TiCl3-AlEt3
Supported catalyst
CH2 = CH2 > CH2 = CHCH3 > CH2 = CHCH2CH3
> CH2 = CHCH2CH(CH3)2 > CH2 = CHCH(CH3)2
> CH = CHCH(CH CH ) > CH = CHC(CH )
Monomer (1-alkene) activity decreases with increasing steric hindrance about the double bond.
Monomer ReactivityØ
2. HETEROGENEOUS Z-N PZN (V)
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> CH2 = CHCH(CH2CH3) > CH2 = CHC(CH3)3
MW and MWDØ
¹ MW would, in most instances, be too high for commercial use.
Chain transfer agents are used to control MW.
Termination of chain growth may occur a number of ways, leading to both saturated and unsaturated chain ends. Saturated chain ends are normally more prevalent in Z-N polymers.
Ti CH2CH2R
R+ CH2 C
Ti + CH CHCH CHR
CH2 CHR
CH2 CHR
2. HETEROGENEOUS Z-N PZN (VI)
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Ti CH2CHR
TiR
+ CH3CHCH CHR
Ti H + CH2 CR
Ti R' +R
CH2CHR'2Al
Ti H +R
CH3CH
AlR'3
H2
CH2 CHR
Mw/Mn > 5 ~ 6
¹ Molecular weight distributions are generally broader when insoluble catalysts are used than soluble catalysts.
The broad distribution may arise from :
2. HETEROGENEOUS Z-N PZN (VII)
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The decay of catalyst activity
The presence of sites of variable activity
¤ Reduce the number or activity of active centers
¤ Encapsulation of active centers by polymer, which prevents approach by monomer
2. HETEROGENEOUS Z-N PZN (VIII)
PZN of DieneF
Catalysts for the Stereospecific Polymerization of Butadiene
Catalyst Yield (%) Polymer structure
R3Al + VCl4 97−98 trans-1,4R3Al + VCl3 99 trans-1,4R Al + VOCl 97−98 trans-1,4
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R3Al + VOCl3 97−98 trans-1,4R3Al + TiI4 93−94 cis-1,4R2AlCl + CoCl2 96−97 cis-1,4R3Al + Ti(OC6H9)4 90−100 1,2Et3Al + Cr(C6H5CN)4
Al/Cr = 2 ∼ 100 syndiotactic-1,2Al/Cr = 10 ∼ 100 isotactic-1,2
2. HETEROGENEOUS Z-N PZN (IX)
Catalysts for the Stereospecific Polymerization of Isoprene
Catalyst Yield (%) Polymer structure
R3Al + α-TiCl3 91 trans-1,4Et3Al + VCl3 99 trans-1,4Et Al + TiCl 97−98 trans-1,4
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Et3Al + TiCl4 97−98 trans-1,4Al/Ti < 1 95 trans-1,4Al/Ti > 1 96 cis-1,4
Et3Al + Ti(OR)4 95 3,4
3. HOMOGENEOUS Z-N PZN (I)
Metallocene catalysts (茂金属催化剂)FMetallocene catalysts were discovered by Kaminsky late in the 1970s.
TiCl
Cl+ R2AlCl
CH2 CH
CH
CH2 CH2 Low catalytic activity
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CH3 Unreactivebis(cyclopentadienyl) titanium dichloride (Cp2TiCl2)
AlMe3 methylaluminoxanes (MAO)hydrolysis
TiCl
Cl+ MAO High activity for alkene
Low tacticitycocatalyst
3. HOMOGENEOUS Z-N PZN (II)
MAO (methylaluminoxanes)Ø
¹ MW = 1000 ~ 1500
¹ Two proposed structures
CH3
Al
CH3
O
CH3
Al
CH3
O
CH3
Al
CH3
O
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CH3
Al
CH3
O
CH3
Al
CH3
O
CH3
Al
CH3
O
CH3
CH3
Al O Al
CH3
O AlCH3
CH3n
¹ Expensive
3. HOMOGENEOUS Z-N PZN (III)
Metallocene catalystsØ
Z
R R
RR
MX
X
M : Zr, Ti, or Hf
X : Cl or alkyl
R : H or alkylZ : bridging group
C(CH ) , Si(CH ) , or CH CH
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RR C(CH3)2, Si(CH3)2, or CH2CH2
ZrCl2(CH3)2Si ZrCl2(CH3)2C
Me2Si(Ind)2ZrCl2 Me2C(Flu)(Cp)ZrCl2
3. HOMOGENEOUS Z-N PZN (IV)
MechanismF
ZrCH3
CH3
L
L+
CH3
CH3
Al O Al(CH3)O
Al(CH )O
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ZrCH3
L
L
O Al(CH3)Oδ
δ+ Al(CH3)3Zr
CH3 CH3
LL Zr
CH3
CH3
O
Al(CH3)O
Formation of active site(single-site)
ZrCH2
L
L
δ
δ
O
CH2
CH2 CH2
AlO
O
3. HOMOGENEOUS Z-N PZN (V)
ZrCH2
L
L
δ
δO
CH2
AlO
O
CH CH
Possible PZN mechanism for ethylene
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CH2 CH2CH2 CH2
Zr
CH2
L
L
δ
δO
CH2
CH2CH2
AlO
O
3. HOMOGENEOUS Z-N PZN (VI)
Features of metallocene catalystsØ
¹ High catalytic activity (homogeneous system)
10 to 100 times higher than conventional Z-N catalysts
¹ Single-site feature
Ex., Cp2ZrCl2/MAO for ethylene PZN : 108 g(PE)/(g Zr•h)
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¹ Single-site feature
Narrow MWD : 2 ~ 2.5MWD of conventional Z-N catalyst : 5 ~ 6
¹ Altering the structure of metallocene catalysts may control the MW, MWD, and stereoregularity of polymers.
LLDPE, HDPE, i-PP, s-PP, s-PS, etc.
4. SUPPORTED METAL OXIDE CATALYSTS (I)
Phillips petroleum company: Phillips catalyst
OO
O
Cr
Si Si+ 2H CH O
OO
O
Cr
Si Si+ CH 2
OO
CH 2
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Metal : Cr, V, Mo, Ni, Co, W, Ti, etc.
Apply to the production of HDPE, LLDPE.
Support : Silica, alumina, charcoal, etc.
¹ Activities of Phillips catalysts are less than Z-N catalyst.
¹ Stereoregularity of Phillips catalysts is less than Z-N catalyst.
Karl Ziegler (1898-1973)
Giulio Natta (1903 ~ 1979)
COORDINATION PZN
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H.W. :Review exercises: 1, 4 and 5